Sciencemadness Discussion Board

Learning Electronics?

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radiance88 - 10-1-2015 at 13:22

Hi,

I'd like to get a good understanding of how to create and modify electrical setups, starting from simple things like light switches and ramping up to cool and interesting things like perhaps a home-made solar power setup or creating an arc furnace out of scavenged parts.

Unfortunately, I have very little understanding of how any of this works beyond knowing that it's electrons flowing through a wire. I'd like to get my hands on some material that teaches both the theoretical fundamental concepts, while also having DIY stuff that teaches and shows me how to apply them to the real world. I'd very much like to be able to tinker and build anything electrical to my heart's content and not be limited by my rather large ignorance on the subject at the current moment.

So as you can see, I'm trying to get a fully round education with electronic setups, but unfortunately don't know exactly where to start.

Can anyone recommend some good resources or starting material that would help build the tinker in me?

aga - 10-1-2015 at 13:27

Theoretically Chemistry is actually Electronics, although the word 'electronics' means something different.

To get started in Electronics, you'll not go far wrong buying one of these :

http://www.ebay.co.uk/itm/130-IN-ONE-ELECTRONIC-PROJECT-LAB-...

35 years ago i got one for Christmas, although the case was wooden, and it had 20 less circuits, and no integrated circuits.

WGTR - 10-1-2015 at 18:49

I am much older now, but I got started in electronics when I was around 10. This was around the early 90's, back when thrift stores sold a lot of electronics junk for very cheap prices. $10 could buy a shopping cart full of old radios and other junk. I picked up many old vacuum tube radios, old stereos made from through-hole components, and many cordless phones when I was interested in finding crystals and surface mount components. I even found a nice vacuum tube Pioneer stereo tuner, complete with a cool "magic eye", that I took apart :( for the nice air variable capacitors. I got my first signal generator (a General Radio 1001A) and oscilloscope (Tektronix 547) at a thrift store. This was also before you could "just Google it". One had to go to a place called a "library" in order to learn things.

Times have changed, but some junk stores still sell old home electronics from the 80's. Those are good places to get useful components on the cheap, if the individual electronics parts in the radios are old enough to be large, big enough for a beginner to harvest and use with hand tools. I wouldn't recommend getting started with surface mount components, as this adds an extra layer of frustration right at the start. Of course, now there is eBay, and a plethora of other online merchants that can sell you whatever you want, and have it delivered the next day.

Some of the first radios that I built used vacuum tubes and big, air-variable capacitors. The tubes were really cool looking devices, and their filaments made them glow in the dark. I'd use gas regulator tubes for voltage regulation, because those would glow pink from the ionized gas. It was really something, sitting in a dark room watching the tubes glow, tuning through the local AM radio stations with those big variable capacitors, knowing that it was a radio I built myself. I built some crystal radios, that use just a half a dozen parts or so. Crystal radios aren't powered, they use the power from the radio station itself. I remember picking up Radio Nederlands on my crystal radio shortwave set late one at night. It was such a powerful signal that I had no trouble picking it up, even on the other side of the world. Back then there was no "internet" as we know it. Listening on shortwave was like getting "secret" information directly from other countries. It was all very, very, cool.

If there was one thing I would do differently, it would be to go back and learn as much math, as early on as I possibly could. It wasn't until college that I took Calculus. Once I did, I realized how much I had been missing in electronics. Even using complex algebra though, electronics understanding comes alive. Resistors, capacitors, inductors, etc., can all be defined using complex algebra. For example, a pure resistance is R +0j, a capacitance is 0 - (j/2(pi)fC), and a pure inductance is 0 + 2(pi)fLj. These can be added, multiplied, divided, etc., to determine the complex voltages and currents at different nodes. Without math, one will be limited to using other people's cookbook designs. This is OK for a beginner, but the lack of flexibility quickly becomes frustrating.

Here are a couple of decent reads that I have encountered:


IMG_0871[1].JPG - 1.5MB

They are pretty cheap, even when new. I still recommend, though, going to a library. If one doesn't have what you are looking for, then go to another one. Colleges that offer engineering degrees often have a very diverse selection in their libraries. My particular one has several full stacks of electronics books, from the early 1800's up until the present.

smaerd - 11-1-2015 at 05:23

I am still an electronics hack. The way I was introduced to it formally was in my college physics courses. I feel like that was the best way for me to learn the fundamentals because not only was it, "this is a resistor, this is a capacitor, etc" it explained what capacitance was, what potential was etc. Of course that sort of knowledge is not necessary to build circuits really but I found it valuable to know those things before going into kirchoffs rules and before going into AC circuits (complex algebra).

So my recommendation is to go to a used book store and grab a calculus based college physics text-book for a couple dollars and read the electricity and magnetism section. Work a few problems, check your answer, then use the internet as a resource if you get stuck. Again you don't need to know gauss's law to build a simple circuit but having an understanding of the principles of electricity and magnetism is good and interesting :).

But yes for simple circuits knowing linear algebra, or even differential equations can help out big-time. These days there are soft-ware/free-ware suites that take a lot of the real 'work' out of circuit design by employing the SPICE engine. I have yet to have any of those programs work for me so I tend to do manual analysis, but your mileage may vary.

Metacelsus - 11-1-2015 at 08:54

I recommend TINA-TI (from Texas Instruments) as a good free circuit simulator. I used it to design my induction heater, and I found it to be pretty accurate.

Little_Ghost_again - 11-1-2015 at 10:27

For high end sims use LT SPICE you can get it free from linear technology web site, there is a yahoo user group as well for it thats a must join kinda thing if you want the most from it.
Join a forum like electrotechonline or one the others as most electronics forums are pretty much the same.
If you think chemistry is expensive then be prepared for a shock lol, eventualy you will wonder into microcontroller's and then you will find that opinions on which micro is best are like which colour is better.
I have my faves but most likely you will be steered down the ATMEL route and arduino, unless you want to get really serious the3y are about the easiest and by far the quickest way to do something micro without all the learning as most the routines are pre written.
Get high end serious and you need to look at stuff like energy micro (now silicon labs) and there CORTEX based GECKO range which is 32 bit and some seriously powerful micro's in the range right upto Cortex M4 with 1meg program space, but forget those for now as they are BGA package and your looking mainly for DIP stuff for now, get a DECENT bread board (maplin do a blue one thats good).
Get a half decent multi meter and a couple of cheap ones.
Get a pc power supply and use that as a general PSU for electronics. Dont get fooled into a full on lab supply at this point as you can do most things you need in the first year with a pc PSU and a few voltage controllers or transistor circuits.
Use ebay and china for parts, use common sense and choose the sellers with reasonable feedback, its china so dont hold 6 week delivery against them if thats all the neg stuff says in there profile.

USE LEAD FREE SOLDER ONLY FOR ANYTHING YOU WANT TO EAT AFTER!
Seriously the biggest tip I can give is get decent LEAD SOLDER, DO NOT use solder for plumbers as the flux will eat your little circuits up in no time. Buy a half decent £45 soldering station and not a £10 soldering iron (thank me later).

Electronics is easier than chemistry and rarely does it ruin clothes or carpets. Resist the urge to get an oscilloscope until you know why you need one.

Erm enjoy and have fun but please join a decent electronics forum they are a great help.
One other thing stay the fuck away from flyback transformers and MWO transformer and all other high or mains voltages until you have some decent experience behind you, despite what some say the truth is more die per year with electric than by blowing themselves up! 50KV from a neon sign transformer wont hurt a bit but you also wont get a second go at the cherry.

I guess as a comparison on here.................. As they say, if you have to ask how to make phosgene safely then dont make it. same with HV stuff, if you need to ask your not ready.

I once got a small kick from a very old car ignition coil, non lethal but man not something you wanna do for fun, a MOT or flyback is another league from that, it jumps towards you if your grounded and 2-3 inch gap is no problem, once its reached you rarely do you get to try it again.


Sorry for the ELF and safety stuff but so many people at the moment on electronics forums asking about jacobs ladders etc. Perfectly safe with experience and caution, but you need both not one or the other



Whats your location?

[Edited on 11-1-2015 by Little_Ghost_again]

Fulmen - 11-1-2015 at 11:55

I don't have any good online sources for you, but I'm sure you'll find them if you try. I think you should start with Ohms law and Kirchhoff's circuit laws, They provide the basic understanding between voltage, currents and resistance. You should be able to calculate the current through a resistor at any given voltage and to calculate the resulting resistance of resistors in both parallel and serial configuration.

aga - 11-1-2015 at 14:29

Quote: Originally posted by Little_Ghost_again  
Buy a half decent £45 soldering station and not a £10 soldering iron (thank me later)

That is probably the Best advice given so far !

elementcollector1 - 11-1-2015 at 14:42

Quote: Originally posted by aga  
Quote: Originally posted by Little_Ghost_again  
Buy a half decent £45 soldering station and not a £10 soldering iron (thank me later)

That is probably the Best advice given so far !

Seconding these words of wisdom.

Fulmen - 11-1-2015 at 16:10

Agreed, I struggled with cheap irons for decades before realizing that even infrequent use merits a decent station.

Also, if you're making PCBs you should seriously consider a photopositive system. I made a small developer box from a bug zapper, combined with a CAD-system like Eagle CAD you can make complex and detailed prints with little effort.

WGTR - 11-1-2015 at 18:38

Quote: Originally posted by Fulmen  
Agreed, I struggled with cheap irons for decades before realizing that even infrequent use merits a decent station.

Also, if you're making PCBs you should seriously consider a photopositive system. I made a small developer box from a bug zapper, combined with a CAD-system like Eagle CAD you can make complex and detailed prints with little effort.


I used the cheap $4 irons from Radio Shack for a long time. They took about 5 minutes to heat up, and didn't have any temperature regulation to speak of. I burned the tips repeatedly. When I got a "real" job, I acquired a nice $400 iron. It warms up in 10 seconds, is temperature regulated, and has a multitude of replaceable tips of all sizes. As for the Radio Shack type...never again.

I'm busy with other things for the foreseeable future; but if there is any interest, I will consider showing how to make circuit boards later on. I use a dry-film photopolymer from Think and Tinker Ltd. They also supply the drill bits I use. The film comes on 100' rolls, but the cost is something like $1 per foot. One roll is a lifetime supply for hobby use.

There are different ways of fabricating the board. Using negative artwork, the film can be used directly as the resist with ferric chloride etchant. With positive artwork, the film is the mask for tin plating. The plating is the resist for an ammonia-copper sulfate etch. The latter option is best when doing through-hole plating.

Little_Ghost_again - 11-1-2015 at 19:23

I use photo boards for final boards or boards that need top quality, But I do get very very decent results with using a HP laser printer and the toner transfer method.
If using toner transfer then the following will save you hastle.............
Clean the copper extremely well and handle with gloves at all times, you need a polished surface that has a very very fine roughness for keying, I use brasso for the first clean then I use IPA and acetone to clean off, after this I use a combination of fine rockwool with Diamtamaceous (sp?) powder and rinse this clean with IPA again.
Use a decent modified laminator and as soon as you have done the final board clean do the transfer within 30 mins. Pre heat the PCB before and during the transfer, DONT bother using a iron!!
It takes some practice but with toner I can get 10mil tracks easy. I have yet to find a better toner than HP origanal! Set printer to use best quality and adjust so the printer uses max toner, the main thing is make sure the board is super super clean and NO FINGER PRINTS!!!
It can be frustrating to get right but the good thing is use a magnifying glass or microscope and check the tracks before you develop the board, its easy enough to take the toner off with acetone and reclean if the tracks dont come out right, dont waste time trying to piss about with sharpie pen if a track didnt stick! It normally happens if your board isnt clean enough or has too high a mirror finish (you need super fine scratches to key in and make the toner stick well.
Take time preparing the PCB board before trying to get the toner to stick on it, I make many many boards this way and although it can take a while to get right it can give great results!
I have also started to use silk screening but so far results are not great at really fine track widths.

While learning use perf/vereo board! its pretty good for quick boards and less hastle than making a PCB.

PRACTICE soldering and except that learning to solder takes time to get right, lead free solder is a bastard and I wouldnt use it until you solder like a pro and by that time you wont want to use this evil nonsense anyway, I think in the states the brand you want is Kester? and in the uk use Multicore electronics solder, most things can be soldered with 0.7mm solder, 1mm for wire soldering and smd is best with 0.5-0.3mm.
I have used some cheap chinese solder and depending on the batch it can be good, but while learning use the good stuff as its easier to get decent results.
most of your non working boards will be down to poor quality solder joints, so dont skimp on decent solder or a decent soldering station (they are pretty cheap these days).

Dont buy a fluke multi meter unless rich as you wont need it and the money is better spent elsewhere.
Use a digital meter to start with, analogue have there uses but while learning a DMM with auto range wont cost much and does a decent job. Dont bother getting one that has 1000 functions you wont need, if you use 240V (or any mains voltage) then get and use a half decent meter with DECENT probes!!
Whats your location? if your in the Uk I can give you some decent ebay names to get stuff from.

radiance88 - 11-1-2015 at 23:32

Okay, I have no idea what most of you just said in this thread, but I got copies of the books that WGTR recommended, and am now looking into getting some kind of circuit board I can play with as per Aga's advice.

Ideally the resource I'm looking for is a bit of both DIY and electronics theory, where the two go at more or less an equal pace. I don't know how much of electronics theory is actually applicable to a hobbyist, I would hate to learn and memorize a ton of complicated formulas and theories only to find out that I needed to know much less. Essentially I just want to break apart things and make new things with them.

IrC - 12-1-2015 at 00:56

http://williamson-labs.com/

This site has a wealth of information aimed at helping one learn electronics. You should get a good proto-board since with one you can quickly build circuits, work out problems and then consider making circuit boards of a more permanent type. One option other than making a PCB is to use perf boards. These along with wire wrap wire and a decent wire wrap tool can make building many circuits easy. For very large complex circuits (especially digital with many traces) one must consider becoming skilled at making a proper etched PCB.

http://www.ebay.com/itm/2860-Points-PCB-Solderless-Bread-Boa...

http://www.ebay.com/itm/830-Tie-Points-Solderless-PCB-Breadb...

http://www.ebay.com/itm/4-pcs-5-x-7-cm-DIY-Prototyping-Perf-...

http://www.ebay.com/itm/New-JDV-HSR224-Tel-Hand-Wire-Wrap-Un...

http://www.ebay.com/itm/JDV-PRODUCTS-Strip-Wrap-Unwrap-Modif...

http://www.ebay.com/itm/30-AWG-Kynar-Wire-Wrap-UL1423-Solid-...

http://www.ebay.com/itm/30-AWG-Kynar-Wire-Wrap-UL1423-Solid-...

For quickly building a low to moderately complex circuit these tools work well if one considers the time involved in working out the artwork, exposing/etching/drilling in order to create a more permanent PCB. One soon learns to weigh the complexity and time when deciding which method to use. Of course when the frequency involved gets high or in circuits where there will be appreciable current flow (look at factory boards where the trace is wider) the perfboard will not be a good idea. However for a large number of projects over the years this method has worked out well for me. At the very least the methods listed above work well for one just beginning to learn electronics. One can rapidly build circuits and test ideas, reusing the parts over and over. Also helps to acquire a supply of various components to build and experiment with. You can go a long way at reasonably low cost using these methods.

Fulmen - 12-1-2015 at 01:20

For experiments a solderless breadboard is invaluable. For PCBs there are many options from acid-resistant pens and transfer decals to photopositive and toner transfer. Toner transfer is cheap and require little equipment, but in my experience it does require a fair bit of experimentation. For the occasional board photopositive is simpler to master.
Other equipment? A digital multimeter of course, you cannot do electronics without being able to measure. An oscilloscope is even better, but they aren't cheap so you might want to hold off on that until you know this stuff is for you.

As for theory you need to cover the basics like Ohms law first. The math isn't that complicated, it's more about understanding concepts. Once you understand the relationship between voltages, currents and resistance you'll have a foundation for further knowledge. Capacitors will probably be the next logical step, after that you'll probably figure out the road ahead yourself.

phlogiston - 12-1-2015 at 12:15

+1 buy a breadboard.

If you buy one book, buy "The art of electronics" by Horowitz and Hill.

aga - 12-1-2015 at 15:34

Buy the 130 in One toy/kit.

You'll learn by Doing, which tends to be much more fun than learning by reading.

The book might say : Wire A to junction X, Wire C to junction Y - the light comes on.
You can then see what happens if wire A goes to Y instead, and safely.

For 20 quid i cannot think of anything more fun, informative or useful for you.

3 years after i got it's ancestor (120 in One) for Christmas i had my first design published in Electronics Today International.

Yes, i re-invented the syn-drum.

At that time all music synthesisers were focused on keyboards.

Aged 15 i failed to even think to get it patented, and was ecstatic with the 175 quid ETI paid me, and having my name in the article published in their magazine.


[Edited on 12-1-2015 by aga]

radiance88 - 15-1-2015 at 01:19

Ok, so update - I was trying to get one of the 300-in-1 lab kits locally online, but it looks like the one item in my area already got sold. There was another one being sold around for 200 USD.. I can buy a hotplate with that kind of money.. so I just passed on that one too. Importing one from the States doesn't fare much better considering shipping costs.

So unfortunately I won't have the quick and fun learning experience from one of those kits (they really do look fun and informative!), but I did have the fortune of actually finding a shop here that stocked breadboards, and small DIY kits which consist of parts and not-so-explanatory, 1 page instructions.

Another bump in the road for me is that to actually use any of them, I have to solder together one of their variable power supply kits first, despite not knowing anything about them, or knowing how to solder stuff properly.

So, tomorrow I'm heading out and buying a breadboard, multimeter, a power supply kit and an FM radio kit despite not having soldered a damn thing in my life. May God (and Youtube) help me.

Magpie - 15-1-2015 at 10:26

There is no need to buy or build a power supply, unless, of course you just want the experience. If you can find a junked computer you can salvage a dc power supply for nothing. I did this using my junked Gateway PC. It's 145w; those of today are probably of higher power. Mine is shown in the picture below. It supplies both 5vdc and 12vdc.



dc power supply.jpg - 134kB

WGTR - 15-1-2015 at 11:12

If you feel like you need it, some of us here could probably help you get the kits put together. Feel free to post pictures with your questions.

If you are making a small little toy FM radio transmitter, then all you probably need are some batteries and a battery holder. No power supply needed. What voltage does it require? It may work with a 9V battery.

Can you identify what model of meter you're thinking of buying? We could help steer you clear of something that won't be useful to you. Same question about the soldering iron. Solder should be rosin flux-core solder, designed for electronics work (no acid core solder that is used for plumbing). It has the flux inside the solder. A good solder wire diameter is 0.6mm (25mi) for the type of stuff you're thinking of.

Here's a basic setup:


IMG_0881.JPG - 2.2MB

There are safety glasses, small pliers and clippers, de-soldering braid (for removing solder), a spool of flux-core solder wire, an acid brush (for cleaning), a soldering iron, a bottle of liquid rosin flux, and a bottle of alcohol (ethanol preferably, but anhydrous isopropanol OK, or acetone).

Normal solder melts at about 183°C. It joins two parts together by forming an intermetallic layer between the two parts and the solder. This happens easily when the parts are clean, but there is always an oxide layer on the metal parts. The flux inside the solder cleans these oxide layers off, allowing the solder to bond to the metal parts. Sometimes if the parts are very dirty, the flux inside the solder is not enough. In this case, extra flux needs to be dripped onto the joint. Flux is your friend. When in doubt, flux it. The alcohol and the brush are used to clean off all of the flux afterwards. Flux is sticky and tends to get everywhere, so be forewarned...

Soldering is an art, and I was put through a 1 week training course when I was first hired. The basics are pretty easy, though, and I'm sure you'll do fine with the Youtube tutorials.

The Volatile Chemist - 15-1-2015 at 12:51

Quote: Originally posted by elementcollector1  
Quote: Originally posted by aga  
Quote: Originally posted by Little_Ghost_again  
Buy a half decent £45 soldering station and not a £10 soldering iron (thank me later)

That is probably the Best advice given so far !

Seconding these words of wisdom.

Thirding it. The reason why I'm unable to solder stuff is because my $10 soldering iron's coil arced while I was using it, and fried/severed both power wires...

Hawkguy - 15-1-2015 at 19:20

Hey if you're working with electronics for the first time, try dissembling/ modifying basic electronics with the help of a book which tells you what everything is... Its actually kinda enjoyable, and feels a bit like actually DOING something... Playful stuff is cool too, like making a shocker from a disposable camera, or a radio controlled fireworks detonator from whatever...

woelen - 16-1-2015 at 00:07

You can simply play with electronics and try to build all kinds of equipment, but for me the real fun has been in understanding electronics. The following basic things you really have to understand:

- voltage, current and power, relation to other SI-units
- Ohm's law
- resistors, linear
- capacitors, inductors (understanding them qualitatively is not hard at all, if you want to do computations on them, then you need some math, using derivatives, integration and maybe some differential equations). There are shortcuts, however, such as computations of cut-off frequencies and resonance frequencies, if you don't have the calculus-knowledge but still want to have some quantitative insight in circuits.
- basic operation of diodes
- basic operation of transistors, the concept of amplification, different types of transistors.

Additionally, if you want to build electronics, using somewhat higher level components than what is mentioned above, then try to understand the following:
- operational amplifiers (opamp), ideal opamp, real opamp as you can buy it
- digital logic (AND, OR, NAND, XOR), both mathematically and as components which you can buy.

From a practical point of view, if you want to experiment with electronics, then I would checkout eBay, chinese sellers. There is a lot of very cheap electronics, which is good, certainly the basic stuff. As a starter, I would buy the following:

- resistors (E12-series, anything from 1 Ohm to 10 MOhm, 10 pieces each). Cost is just a few dollars including shipping from Chinese suppliers.
- capacitors (100 pF, 1 nF, 10 nF, 100 nF, 1 uF and maybe also 330 pF, 3.3 nF, 33 nF, 330 nF). Also dirt-cheap from eBay.
- a bunch of opamps (TL071, TL072 are decent ones, which are good for most electronics projects and cost less than $0.50 per piece).
- a set of transistors (BC547 and BC557, 10 each). For these sets you most likely also will have to pay at most a few dollars.
- a set of diodes (1N4148 and 1N4006, 20 each). These really are cheap.
- some power regulators (e.g. 7805, 7806, 7812).
- a set of LEDs (different colors, 3 mm transparent glass-like ones are cheap)
- some digital logic circuits (74HC series, lookup wikipedia for type numbers), e.g. NAND gates, AND gates, OR gates, some more advanced building blocks like flip-flops, latches and so on.
- some special function chips to get an understanding of modern electronics, where special functions are put in a single chip. Nice examples are:
> So-called 555 circuit. This is a versatile thing, allowing you to build timers, oscillators, and many other circuits, from which you can learn a lot. Buy a few of these, cost is just a few dimes per piece.
> LM335/LM35 temperature sensors
> Hall-effect sensor (lookup eBay)

You also need a breadboard/experimenters board and you need a good soldering station. These are discussed before. A decent digital multimeter, which allows you to measure voltage and current also should be included. You can buy these as well from eBay, from some chinese seller. No need to spend a lot of money on that. A basic symmetric power supply (e.g. 2x 15 volts, capable of delivering a few ampere will be OK for most experiments).

I did an experiment with electronics, just for fun and scientific insight, which gives you an idea what kind of components you need and how these things can be described mathematically. It is a very simple piece of electronics, made on a breadboard, but the behavior and math behind it is quite interesting:

http://woelen.homescience.net/science/math/exps/rossler_chao...

radiance88 - 20-1-2015 at 06:33

Ok.. update:

I went out and bought myself a multimeter, breadboard, solder sucker and two kits - a power supply one and an AM/FM radio one. We already have a soldering iron and solder at home. My multimeter is digital and has auto-range and also measures temp, which I intend on using on some experiments.

I bought the power supply because it seemed pretty essential given the fact that the other kit ran on 12 volts, and the 12-volt battery they were selling needed some other expensive thing to charge it (according to the guy at the counter, said they didn't have anything else), so this is what I have. btw my country uses 220 volts.

The parts for the power supply are down below:


And this is the diagram that it's supposed to follow:


I'm still trying to figure out how to wire the transformer and the switch. The transformer has one side with 6 wires saying 12V, 9V, 6V, 4.5V, 3V, 0 while the other says 220V, 110V, 0. So I'm guessing that the zeros are negatives.

The switch looks like complicated little piece of equipment. The bottom has an inner row of pins with holes in them, 2 of them. The second row outside of that has 12. Not sure what goes with what.

I'll read more on this circuit later when I get out of work. It includes no manual so I have to figure out how to wire everything based on the diagram alone.

I'll try to see if I can experiment with making it on a breadboard because I don't want to solder everything together only to realize that I screwed up.

woelen - 20-1-2015 at 07:26

If you want to connect the transformer to your 220 V wall outlet, then connect the 0-connection at the left (this is the primary side of the transformer) to one wire of the outlet and connect the 220 V connection to the other wire of the outlet. Leave the 110 V wire unconnected.

The secondary side has many taps with different AC-voltages. By means of the switch, you select one specific tap and the voltage of that tap is rectified by the circuit with the diodes and capacitor. The LEDs and 1 k resistors give a visual clue which tap is selected and the 1 k in parallel to the capacitor is a bleeder resistor, which assures that if the power is disconnected, then the energy, stored in the output capacitor slowly is dissipated and it also assures, that if the selector switch goes from a high voltage to a lower voltage while there is no load connected, that the output voltage slowly goes to the lower voltage. Without the resistor, the output voltage could remain at a high voltage for a very long time if the supply is switched off or switched to a lower voltage.

WGTR - 20-1-2015 at 11:08

I think that everything Woolen said is correct. Here is a bit more descriptive schematic than what they gave you:

circuit.jpg - 626kB

I suggest assembling the circuit board first. Where you would normally connect the rotary switch from the transformer, instead connect a 9V battery. Measure the voltage on the output with the voltmeter. It should be about 1.5V less than the battery voltage. Now reverse the battery connection. The output should still be the same voltage, and the same polarity. The output voltage should not flip polarity when the battery voltage does. Next, switch the meter to measure current, and put it in line with the battery. The current should measure about 7 to 8 mA regardless of battery polarity. If it is much higher or lower, something is wrong.

[Edited on 1-20-2015 by WGTR]

circuit2.jpg - 199kB

radiance88 - 25-1-2015 at 14:20

So far my experience in all of this is that it's been just a lesson in pain.

The first time trying to solder an extra PC power supply plug onto the little transformer wires seemed OK enough. Lots of little globs of solder around the wires and the connection seemed solid enough - however I had a WTF moment when using my multimeter to check the 12V output along with its negative, as I just could not get a steady reading, and it was in the millivolt range. This was using the DC setting on my multimeter. However, using my multimeter's AC setting gives me the desired current!

I'm at a loss for words as to what the heck is going on here.

I decided perhaps it's just sloppy soldering technique, as using the multimeter's AC setting in my wall socket gives me 230V, and testing a 1.5V battery on DC gives me what I'm looking for, so I decide it can't be something wrong with my multimeter.

I cut off the soldered parts and start again using untouched parts of wire. I cannot for the life of me get the solder to go where I want it to go. It either sticks to the tip or avoids seeping into my wires. I know that I should "tin the tip", and that I should heat the wire and feed the solder into the wire to get a solid job. But despite the iron being hot enough to melt the solder on contact, holding it against the copper wire doesn't get it hot enough even after a minute or two of contact to melt the solder.

I say "screw this" and then just try to feed the solder onto the tip and try to drip it downwards into the wire - instead the outside of the drop of solder dries up, and it try to push it into the wire, but it won't stay there and instead falls down onto my workbench.

I'm pissed off enough to take my setup and chuck it all against the wall, but realizing that I can't inflict pain on solid objects, I just pack everything back into a corner.

I'm not sure if my technique, my iron, or my solder is the deal here ,but I really don't think putting two wires together properly should be this hard.

Magpie - 25-1-2015 at 14:27

Quote: Originally posted by radiance88  

I'm not sure if my technique, my iron, or my solder is the deal here ,but I really don't think putting two wires together properly should be this hard.


You are right - don't chuck anything!;)

What is the watt rating of your soldering iron?

radiance88 - 25-1-2015 at 15:10

It's 30 watts. It's a cheap chinese piece of junk, I know, but wouldn't this at least be enough to let me do small jobs like these? Plus it's new, even if it did cost me only a few bucks. I've been advised here a few times to get myself a soldering station, but after spending so much cash on a digital multiranging multimeter with temperature reading, I'm kind of set back awhile before I can make that kind of purchase again.

Magpie - 25-1-2015 at 15:39

That's what I have: a 30w RadioSchack iron. Probably the same one you have. It seems to produce plenty of heat. I melt some solder on the tip, knock off the excess with a knife, place the tip next to the joint, wait 3-4 seconds, then bring the solder down to the joint and it melts! My solder is RS 0.050" diameter, rosin-core.

How long you heat the joint depends somewhat on the mass of metal that must be heated. Care must be taken to not overheat and damage heat-sensitive components.

I don't see where you are doing anything wrong. I would recommend that you just get some scraps of copper wire and practice splicing them together.

Sometimes I need a 3rd hand. For that I've been using my fly-tying vice. :D

[Edited on 25-1-2015 by Magpie]

[Edited on 25-1-2015 by Magpie]

DREDD - 25-1-2015 at 17:04

Hi
I dont post but some of the advice here I totally disagree with!
Electronics my first love.
Totaly self-taught for about 40 years.

You don't have a clue about the subject so here are my tips,

1 Soldering, forget it, for now.
Its an art and will break you before you start.

2 Dont spend any money on tools or kit.

Here is what you should do

Collect lots of unwanted BATTERY ONLY operated devices.(Torches are great)
Start stripeing them down and playing with them and putting them back together.
You will learn loads in a short space of time and it will cost you nothing.
Anyway thats my tuppenceworth and first post.
Best of luck.

WGTR - 25-1-2015 at 19:26

I respectfully disagree with Dredd. Soldering is a very, very, basic electronics skill, and it will become much easier once you get through a few "aha!" moments.

Back when I used the 30W irons, I noted that they took at least 5, sometimes 10 minutes to heat up. The cheap irons have no temperature regulation, and get hotter and hotter as time goes on. Also, 30W is not a very powerful iron, so there will be some large wires that it is simply not powerful enough to solder without assistance. It sounded like you were doing things correctly by adding a small amount of solder to the tip, and then feeding solder directly into the joint as it was heated. Would you mind posting a picture of the problem solder joints?

Some tips for soldering objects with an underpowered soldering iron:

Not only "tin" the soldering iron tip, but also tin each part lead separately before trying to solder them together. In other words, if you're trying to solder a large wire to a heavy pin, try soldering the wire and pin separately first. If the solder flows cleanly over them, then you know that the surfaces are clean. Clean parts like this will solder more readily at a lower temperatures than dirty ones will. It is good to get in the habit of doing this anyway.

If one part simply won't take solder, it is possible that it is covered with a heavy oxide layer. The flux requires higher heat from the soldering iron in this case, before it can clean the joint. If this happens, simply clean the wires with fine sandpaper. On rare ocassions, I have found some old parts to be so oxidized that they were unsolderable without sandpaper cleaning.

If possible, preheat the part in an oven or on a hot plate.
https://www.sciencemadness.org/whisper/files.php?pid=338528&...

In the previous example, I soldered some copper pipe to a copper plate by heating it on a hot plate and feeding solder into the joint. No soldering iron needed.

Eutectic solder melts at 183°C. If your part cannot withstand this temperature, even preheating to 60-70°C in an oven can make it possible to solder a problem joint with a weak soldering iron. Some plastics start softening around 100°C, so don't overdo it.

Normally these extra methods are unnecessary, and the soldering iron will be sufficient by itself.

Another possible problem is that you're trying to solder to aluminum or steel. These metals require special techniques and fluxes, and cannot be soldered with normal electronics solders. I sometimes had this problem, but it sounds like this isn't your issue. Anyway, let's see a picture.

The Volatile Chemist - 26-1-2015 at 11:11

Anyone know of a good site explaining RC (Resistor Capacitor, not Remote control) electronics well? Stuff similar to what tim (the A---- guy, I always forget his name, subtitle 'post harlot', with a username for a guitar petal) does.

aga - 27-1-2015 at 11:24

Depends what you mean/want to build.

Are you talking about time constants or filtering - there's an awful lot of RC circuit theory out there.

Magpie - 27-1-2015 at 13:57

Here's a site full of tutorials:

http://www.electronics-tutorials.ws/rc/rc_1.html

jock88 - 27-1-2015 at 14:48


Soldering is a very basic skill as stated above.
If ya cannot maser some simple soldering ye may quit!

The age of components can make them difficult to solder. Brand new components and brand new board is very easy to solder (using solder with flux core).
Old resistors and caps. that have been around for years have an oxide layer built up on the leads and can be difficult to solder. You may need to clean the leads with a rub of sandpaper or scrape them with a knife. Same for copper strip board and pcb's (thats pwb's for those on the 'other' side).

Some solders have very little flux contained in them. The stuff that you may get out of an electronics factory (take home in your pocket god forbid) where they are always dealing with brand new components and boards, use solder that have very little flux as everything is very clean and new.
Purchase solder with a decent amount of agressive flux (don't know how to ask or obtain it I will admit) in it for doing home stuff that may have more 'rusty' (older) components in the project.

The Volatile Chemist - 27-1-2015 at 15:00

Quote: Originally posted by aga  
Depends what you mean/want to build.

Are you talking about time constants or filtering - there's an awful lot of RC circuit theory out there.

Yes, also power supply workings such as how voltage/amperage is regulated (Not just with a three-prong regulator;)).

aga - 28-1-2015 at 10:24

Oh i see : Electronics in General.

To get started, and experiment, i really cannot recommend this kit highly enough, or enough times :-

http://www.ebay.co.uk/itm/130-IN-ONE-ELECTRONIC-PROJECT-LAB-...

The Volatile Chemist - 28-1-2015 at 13:23

Quote: Originally posted by aga  
Oh i see : Electronics in General.

To get started, and experiment, i really cannot recommend this kit highly enough, or enough times :-

http://www.ebay.co.uk/itm/130-IN-ONE-ELECTRONIC-PROJECT-LAB-...


Aga.... :)
I saw your recommendation, and haven't ignored it, I own that kit (Purchased ~1yr ago) and have gone through it. It does not discuss power supply theory, which is what I'm getting at. But it is a wonderful foundation for electronics, I recommend it too.

aga - 28-1-2015 at 14:45

For power supplies, it all gets down to what you want in the final supply.

Stability mostly, being Voltage, Ripple, Current and Error Detection.

In some cases it's Current limiting or voltage limiting/boosting.

A basic voltage regulator uses a transistor (high power) to regulate the Output voltage in what is called an 'Emitter Follower' configuration.

e.g. http://www.radio-electronics.com/info/power-management/linea...

A 7805/6/8/12/15 regulator is a much more advanced version of this, yet basically the same.

Current limiting tends to be done by current detection, and limiting the Voltage to achieve the required current.

Buck and Boost regulation techniques are brilliant.

They work by using Pulse Width Modulation to either Raise a voltage or reduce it.

Basically you switch current into an inductor on/off at varying rates, and then use the energy in the collapsing magnetic field to power your circuit.

e.g. search www.microchip.com for AN626 , lead acid battery charger

Ripple (DC having a small amount of crap on it) tends to still be mitigated by adding capacitors in parallel with the output.

The Volatile Chemist - 29-1-2015 at 06:48

Thanks. That's pretty much what I was talking about.

aga - 29-1-2015 at 08:57

Interesting (and useful) as Buck & Boost circuits are, most modern standard PSUs (e.g. your laptop charger) use a technique called 'Switch Mode'.

The 230volts AC is rectified giving a DC supply of 324volts (rectify AC with a bridge and you get 1.41 times the AC as DC) which is then switched off/on at between 20~40kHz through a transformer.

The physics of transformers means that the higher switching frequency allows you to use a much smaller transformer than you would at the usual 50~60 Hz for the same energy transfer.

Despite the massive difference in complexity between a simple PSU circuit (with a transformer to take 230vac to 12vac, then a bridge & a capacitor) the reduced amount of transformer material (copper, iron) still makes it cheaper to use switch mode.

Taking the Size and Weight difference into account (=shipping costs) there's no competition, hence almost all modern PSUs are switch mode.

The Volatile Chemist - 29-1-2015 at 14:05

Thanks for the information. That's the kind of stuff I was looking for. If I find Tim's website, or I remember his SM Username, I'll post a link to his work with some sort of induction heating device (rather common in home chem. if I remember), and ask for info. on how it works :)

aga - 29-1-2015 at 15:24

Industrially they call it an 'Inverter'

Basically all the energy gets converted to Radio Frequency energy, and gets absorbed by the Target by inducing currents in them, hence the term 'Induction Heating'.

https://www.youtube.com/watch?v=hw9OmmKVunI

Edit:

Maybe this : https://www.youtube.com/watch?v=pVYMLnXW9uo

[Edited on 29-1-2015 by aga]

WGTR - 29-1-2015 at 17:49

Quote: Originally posted by The Volatile Chemist  
If I find Tim's website, or I remember his SM Username,

12AX7

jsc - 2-2-2015 at 20:19

Sorry to rain on your parade, but unless you are a kid, you can probably forget learning electronics, there is just too much stuff and technique to acquire for an adult whose best learning years are behind them. If you were one of the rare type of adults who have the capacity for adding a big new skill like this, you would not be asking on a forum how to do it, you would already know such things.

In other words, just the fact that you are asking here "How do I learn electronics?" pretty much identifies you as someone who has a 0% chance of getting anywhere with something like that.

I recommend sticking with things you already know how to do, and leverage your precious time where it will do the most good, which is stuff you know, not whole new sciences and technologies.

guanadine - 2-2-2015 at 20:43

The best way to start learning electronics is by doing. you are not going to retain anything you read but when you involve physical movements its like Karate. start by going on ebay and search for electronics kit + op amps. buy a kit for 15 dollars, a 5 dollar solderless breadboard, a cheap voltmeter. and a 12 volt center tap transformer from radioshack. your knowledge will increase exponentially.

Zombie - 2-2-2015 at 21:05

Quote: Originally posted by jsc  
Sorry to rain on your parade, but unless you are a kid, you can probably forget learning electronics, there is just too much stuff and technique to acquire for an adult whose best learning years are behind them. If you were one of the rare type of adults who have the capacity for adding a big new skill like this, you would not be asking on a forum how to do it, you would already know such things.

In other words, just the fact that you are asking here "How do I learn electronics?" pretty much identifies you as someone who has a 0% chance of getting anywhere with something like that.

I recommend sticking with things you already know how to do, and leverage your precious time where it will do the most good, which is stuff you know, not whole new sciences and technologies.



Man that's a negative attitude.
When I'm 80 I hope to begin another career in Rocket Surgery. I just don't have time yet due to the week or two it's going to take learning Organic Chemistry.

The fella has no reason to learn every aspect of electronics, (which by the way can be learned in just a few months for basic electronics). Just a few skills at reading schematics, and understanding which way the water flows. It's no more complex than plumbing, and you don't need a masters to understand plumbing.

I have a dear friend that is a retired Prof. of Electronic Engineering (Stony Brook). He calls me to repair the simple DC circuits in his boat. Not because he does not understand them but because he can not follow the plumbing. The concept of wiring harnesses traveling between decks, and randomly changing color from source to point eludes him.
My point is anything can be learned , and applied.

Call me in 20 years if you need your rocket fixed. I will include free spay or neutering w/ all vaccinations;).

woelen - 3-2-2015 at 00:41

Quote: Originally posted by jsc  
Sorry to rain on your parade, but unless you are a kid, you can probably forget learning electronics, there is just too much stuff and technique to acquire for an adult whose best learning years are behind them. If you were one of the rare type of adults who have the capacity for adding a big new skill like this, you would not be asking on a forum how to do it, you would already know such things.

In other words, just the fact that you are asking here "How do I learn electronics?" pretty much identifies you as someone who has a 0% chance of getting anywhere with something like that.

I recommend sticking with things you already know how to do, and leverage your precious time where it will do the most good, which is stuff you know, not whole new sciences and technologies.

If everybody were reasoning like this, then we still would live in caves and use wooden sticks as our most advanced piece of technology. What you are saying is utter nonsense. You never are too old to teach yourself something new. Of course, you need commitment and you will have to put some effort in it, but it can be done. As already stated before, by doing things you also can teach yourself a lot. Just try things and try to understand what you observe by reading and thinking about it.

The Volatile Chemist - 3-2-2015 at 14:40

Quote: Originally posted by jsc  
Sorry to rain on your parade, but unless you are a kid, you can probably forget learning electronics, there is just too much stuff and technique to acquire for an adult whose best learning years are behind them. If you were one of the rare type of adults who have the capacity for adding a big new skill like this, you would not be asking on a forum how to do it, you would already know such things.

In other words, just the fact that you are asking here "How do I learn electronics?" pretty much identifies you as someone who has a 0% chance of getting anywhere with something like that.

I recommend sticking with things you already know how to do, and leverage your precious time where it will do the most good, which is stuff you know, not whole new sciences and technologies.

Haha, N/A, as I fit the interval (0, 18).
Quote: Originally posted by WGTR  
Quote: Originally posted by The Volatile Chemist  
If I find Tim's website, or I remember his SM Username,

12AX7

Thanks, that's him. He's a great guy (but probably thinks I'm weird :P)
Quote: Originally posted by aga  
Industrially they call it an 'Inverter'

Basically all the energy gets converted to Radio Frequency energy, and gets absorbed by the Target by inducing currents in them, hence the term 'Induction Heating'.

https://www.youtube.com/watch?v=hw9OmmKVunI

Edit:

Maybe this : https://www.youtube.com/watch?v=pVYMLnXW9uo

[Edited on 29-1-2015 by aga]

Also what I was talking about, thanks. I find such devices interesting, but don't plan on building one too soon.

radiance88 - 4-2-2015 at 21:38

So I found out that there wasn't really anything wrong with any of my stuff - it was just me being an idiot, forgetting that a transformer by itself doesn't convert anything from AC to DC power.

I managed to solder the power supply wires onto an old pc power supply cable, and I managed to feed the 12 volt power into a breadboard and tinker around with a couple of LEDs. It was fun seeing my first little circuit light up.

I have a problem though regarding the switch below:



I understand enough to know that each of the 5 voltage wires from the transformer connect onto their own pin on the switch, and pair up with an LED on its complementary side. However, what do the two pins in the middle connect to?

This is the same circuit as the diagram I've posted above.

Zombie - 4-2-2015 at 21:46

Usually 2 pins off alone like that will be either an on / off type thing or a non variate- d pole. b Sometimes input to supply power to all the rest...
I didn't see any schematic or diagram for that switch. Can you describe what it is called or what it is sold as?

radiance88 - 4-2-2015 at 22:17

It actually is up there, but the thread has gotten long so I'll let me post the circuit diagram again:



Right - the kit enclosure has a slot for a power switch, and it includes a power switch.

I guess I screwed up by soldering the transformer directly onto the power cord when I should have soldered the power switch inbetween that?

Or did I do that right, and somehow I'm supposed to solder the power switch to this switch? Do these two pins in the middle need to be connected in order to convey the electricity from on pin to its complementary pin?

IrC - 5-2-2015 at 00:50

You are going to cause yourself a disaster if you do not quit soldering before carefully studying the diagram and following it point by point. If you "solder the power switch to this switch" are you then going to connect the secondary to the primary side of the transformer? The AC line has a hot and neutral. Connect the neutral to the primary '0' on your transformer. Connect the hot through a switch first unless you are going to add a fuse to the input. From power switch on to the hot side of the primary either 117 or 220, depending on where you live (what service you have). Personally I would add a fuse so if you screw up at least you save the transformer. The DP6T switch goes on the secondary side and has no electrical connection to the power line (primary side). The 2 center terminals are your two commons. One goes to six as does the other (other 6). Connect your meter to measure resistance or easier diode beep to one common (center pins).

Rotate switch fully CCW. Now touch outer pins until you hear a beep (if the meter has a diode test, easier than watching ohms display you can keep your eyes on only the switch). Mark terminal on side or wherever handy with fine tip marker. Rotate CW one click at a time and you will hear the beep follow pin by pin around CW until you hit position 6. Now you have one side done. Do the other side after resetting full CCW, or use logic that it just continues on around on the other center common pin. As your switch is 6T, you will have a dead position since you only have 5 taps on the transformer and 5 LED's. The first position will be zero volts, the two corresponding outer pins leave open. The two common's connect together (do this test to know the switch basing first, before connecting the commons together). The 5 corresponding pins on switch 2 (one single rotary body two switches) each get a LED plus terminal, all negatives connect together and go through a single 1K to DC ground (bridge minus). As you rotate your switch you will have 0V, 3V, 4.5V, 6V, 9V, 12V (AC) from the two joined commons to the bridge AC input (top in diagram). What they are doing is giving you 5 LED's stepping up in brightness as your voltage goes up. Secondary 0V goes to bridge bottom (other AC input).

Zombie - 5-2-2015 at 02:26

I just went back to your first post on this thread, and I have to admire how far you have come in one month.
From a "hello" to how do I assemble my voltage stepping power supply. Nice!

IrC of course has it right especially in the notion, you have to slow down, just a little. Learning to use your DMM is perhaps the MOST important aspect of what you are doing right now. It tells you every single thing you need to know. Including which wire goes where.

It's all new, and looks like a bowl of spaghetti. No arguments there. Which end goes where? You might not know but your meter does.
Make yourself a sort of "flow chart". A schematic you can draw on. As you understand a part circle it.
Not just what you can do because you were told but what you can do because you know how, and why you are doing it.

A monkey can assemble a television. It takes a trainer to show the monkey how. Here it comes now... Wax on / wax off. Be the monkey... No I meant Be the trainer... That sounds better.

Once you follow the above post, and learn to ID the poles with your meter, that alone will open new doors to understanding.

Just wanted to say Kudos for your progress. Got long winded.

[Edited on 5-2-2015 by Zombie]

WGTR - 5-2-2015 at 04:15

Quote: Originally posted by radiance88  
So I found out that there wasn't really anything wrong with any of my stuff - it was just me being an idiot, forgetting that a transformer by itself doesn't convert anything from AC to DC power.

Been there, done that.
Quote: Originally posted by radiance88  
I managed to solder the power supply wires onto an old pc power supply cable, and I managed to feed the 12 volt power into a breadboard and tinker around with a couple of LEDs. It was fun seeing my first little circuit light up.

Good job! I knew you'd figure it out. Keep one of the 1k ohm resistors in series with the LED, to keep from burning it out.
Quote: Originally posted by radiance88  
I have a problem though regarding the switch below:

I understand enough to know that each of the 5 voltage wires from the transformer connect onto their own pin on the switch, and pair up with an LED on its complementary side. However, what do the two pins in the middle connect to?

This is the same circuit as the diagram I've posted above.


If you look at the little schematic I posted earlier, it has 14 pins. There are six pins for the switch positions on both switches (12 pins), plus 2 more for the rotor connections in the middle, giving a total of 14 pins. The two rotor pins, when connected together, get connected to the bridge rectifier.

Don't take my word for it, check it like IrC said. Put the knob on the shaft and rotate it around, seeing how the switch connects in different positions. It's actually quite an interesting switch. After connecting the two middle pins together, the switch should connect straight through from the transformer side to the LED side as the switch is rotated. This can be verified with the "diode" setting on your multimeter. The meter should "beep" with this setting when the switch connects. This function can be verified by touching the two meter probes together. If there's no beep, then you're stuck using the ohmmeter. It should read 0 ohms when the switch closes (connects), and very high or "OVLD" when the switch is open.

IrC - 5-2-2015 at 05:06

Good work WGTR I never looked at page 2 to see your diagram, would have saved me a bunch of words. Your circuit is how I would wire it, fuse first then switch with switch opening both lines. So many houses especially older ones have hot/neutral reversed from code. Although in the EU with 220 I cannot imagine how that matters since both lines are hot making a DPDT power switch even more logical (does the EU wiring have a 3 pin or 4 pin plug, and separate neutral and earth pins?).

Maybe a verbal description was not redundant, if one cannot read a diagram sometimes a verbal description helps. I have several Flukes because of all my many meters the beep is loudest on the Flukes. Nothing beats keeping your eyes on the work using sound as an indicator. Especially when trying to work out a complex switch like his DP6T.

After around 25 years of aging I have noticed one must go on a hunt for the right piezo disc as the Fluke beep gets weaker. Happened on 3 of my Flukes so far which I bought in the early 80's. Gently burnishing the terminal plating on the piezo disc every 6 or 8 years helps only so many times.

Magpie - 5-2-2015 at 11:24

Quote: Originally posted by WGTR  

Quote: Originally posted by radiance88  
I managed to solder the power supply wires onto an old pc power supply cable, and I managed to feed the 12 volt power into a breadboard and tinker around with a couple of LEDs. It was fun seeing my first little circuit light up.

Good job! I knew you'd figure it out. Keep one of the 1k ohm resistors in series with the LED, to keep from burning it out.


I think this is a very good example of how knowing a little about the mathematics of electronics can be very helpful and satisfying. For example, I have some red LEDS that are rated at 2.6v and 28ma. Now, if I attempt to power this LED with my 12v supply I may well get one intense red flash just before it burns out! The way I deal with this is to use Ohm's Law, E=IR, as follows:

Compute the LED operating resistance, R, as:

R = E/I = 2.6v/0.028a = 93 ohms (Ω)

I must limit the current to a maximum of 0.028a, so for 12v,

R=E/I = 12v/0.028a = 429 Ω;

So the total resistance of the LED circuit must be no less than 429Ω. Therefore I must place a resistor in series with the LED having a value of no less than:

429Ω - 93Ω = 336Ω.

This will light the LED at its rated voltage of 2.6v. My circuit will consist of a 12v terminal, the LED, the 336Ω resistor, and ground (O volts), all in series.

Experienced people like WGTR and IrC, don't do these calculations, I imagine. They know to just add a 1k resistor in series with the LED, giving them a generous safety factor.



[Edited on 5-2-2015 by Magpie]

[Edited on 5-2-2015 by Magpie]

Zombie - 5-2-2015 at 11:33

The 1k resistor is kind of a standard when dealing w/ +12v DC.
I retro fit boats / motorcycles / cars / ect... , and have boxes full of different color LED's, and rolls of 1k resistors.

Not to take anything from the post or the gentlemen. Knowing the formulas is mandatory in electronics.

IrC - 5-2-2015 at 11:49

"They know to just add a 1k resistor in series with the LED, giving them a generous safety factor"

Very true. For 14 volts DC I use 680 but have seen them burn out after several months so 820 to 1K is going to light it as well as letting the LED live long. Also being 12 VAC peak voltages must be considered meaning 1K is just an overall good choice. Using 5 LEDs seemed to me to be an attempt to indicate voltage by brightness. Would make sense also to mount LEDs in arc around switch pointer one for each 'on' position from low to high voltage.

aga - 5-2-2015 at 11:59

There a many 'rules of thumb' to use, or simply steal the 1k value from a published design that also uses a 12v supply.

However, there is no substitute for knowing the maths behind such values.

With an LED, the worst you can get wrong is that the led blows.

With higher power stuff, the maths become a Safety tool e.g. :

Short a 12v car battery out with a spanner.
Steel is about 6x10-7 ohms per meter (depends on the composition) and the spanner is about 33cm long, so let's guestimate it has a resistance of 2x10-7 Ohms.

I = V/R, so the maximum Amps flowing will be 12 / (2x10-7) = 60 MILLION Amps !

The battery would be unlikely to supply so much, but Something would certainly explode.

With a car battery, it's usually the spanner.

IrC - 5-2-2015 at 13:55

"The battery would be unlikely to supply so much, but Something would certainly explode. With a car battery, it's usually the spanner."

Having been the same room where this happened not once but 3 times over the years, not so much. The battery explodes faster than it can destroy the wrench. No doubt rapid large volumes of H2 with air ignited inside blowing the case apart with a loud bang spewing acid over a large area. I have seen it happen but luckily never been in the path of the acid. Mostly because I pay attention working on such things but never trust that someone else does. This I learned multiple times. The loudest bang was a metal battery box on a 2 ton step van where the worker let the lid fall closed with the battery sitting on top a wooden block meant to be put in front of the battery so it did not slide around inside the box in use. The 1/4" thick rectangular steel lid slammed home against both top terminals. In all these examples batteries were fully charged up (or new), 800 to 1,000 CCA. Result is loud explosions blowing case apart. In none was I in the line of fire from the spraying acid lucky me. However I did learn to have great caution being around someone working on a vehicle.

One time (4th) incident, a guy was using a long 7/16" box/open on a battery terminal. He rotated it not paying attention until the open end contacted the plus terminal with the box end still on one of the cable bolts of the negative terminal. Battery was not fully up which saved him, his face was right there in front of the battery. The wrench instantly welded itself between the two terminals starting to glow red in the center fairly quickly with steam blowing out the fill caps. As he yelled from the searing burn in his hand, letting go of the wrench just not quickly enough. Lucky him he lost a shirt and jeans but not his face or eyes. Tried washing them at home and they started disintegrating. Depending upon many factors including the state of the battery and capacity, combined with the ability to conduct amps in the short, more often than not in my experience they just explode launching acid all around. My ears rang on the step van incident louder than they would have if a 12 gauge was fired in the room. It was a very loud explosion.

Fulmen - 5-2-2015 at 14:22

Agreed, do the math until you can make your own judgment calls. Don't just rely on others numbers, that isn't going to get you anywhere.

As for Magpies numbers I'm sure he's right, but there is another perhaps more useful way to approach the math. With semiconductors there is not necessarily any real ohmic properties, meaning that it does not have a fixed resistance like a light bulb or an resistor. So while you can calculate the resistance for any given conditions it is somewhat misleading. I prefer to approach it like this:
The led can withstand a maximum current of 28mA, and at this current it exhibits a forward voltage drop of 2.6V. If you are to feed it from a 12V source you need to drop the voltage to 9.4V. At a current of 28mA this voltage drop is produced by R=U/I=9,4V/0,028A=336Ω.

IrC - 5-2-2015 at 16:23

Quote: Originally posted by Fulmen  
Agreed, do the math until you can make your own judgment calls. Don't just rely on others numbers, that isn't going to get you anywhere.

As for Magpies numbers I'm sure he's right, but there is another perhaps more useful way to approach the math. With semiconductors there is not necessarily any real ohmic properties, meaning that it does not have a fixed resistance like a light bulb or an resistor. So while you can calculate the resistance for any given conditions it is somewhat misleading. I prefer to approach it like this:
The led can withstand a maximum current of 28mA, and at this current it exhibits a forward voltage drop of 2.6V. If you are to feed it from a 12V source you need to drop the voltage to 9.4V. At a current of 28mA this voltage drop is produced by R=U/I=9,4V/0,028A=336Ω.


Except of course everyone is ignoring the fact that it is 12 volts AC not DC, nor considering the actual LED. Is the 12 volts being considered as an RMS value and if so, running it at 28 ma based upon this voltage will cause what peak current in the LED? One should also consider the led specs as 28 ma is arbitrary itself. Is it a 5,000 or 25,000 mcd LED? Neither does 28 ma consider the LED lifetime and I can say from experience running the LED at it's maximum ratings it will burn out sooner than you think.

Resistance can be determined with a semiconductor given its specifications such as Hfe (for a bipolar device as example), knowing where it is on the curve for given conditions. For an amplifier one would bias it in the middle of the curve in the linear portion which would allow one to calculate the Collector load impedance. I won't go into all the various parameters in this casual conversation. Links have been given for very good sites which cover this in depth. In any case I can tell you from my experience you can trust the 1K mentioned under the conditions the circuit presents, which also allows some de-rating for a long LED life even with the AC being considered.

"Experienced people like WGTR and IrC, don't do these calculations, I imagine."

Yes and no depending upon the case under consideration. I don't even want to recall the mind numbing hours running calculators over the years when designing a circuit. Very important in any high power situations. In fact one cannot escape the time consuming work especially designing say an amplifier where linearity and bandwidth are important. If the OP has a goal of learning electronics then he must start studying the math in depth, learning to use Spice or something similar, and practicing soldering skills. Just never overload yourself all things take time and patience.

Zombie - 5-2-2015 at 16:44

This may be the single most valuable quote in this entire thread. Ask a zombie...

Quote IrC:
" I pay attention working on such things but never trust that someone else does."

I live my LIFE by this one simple rule.

WGTR - 5-2-2015 at 17:01

Most of what I do in electronics is math-based. However, I suggested using a 1k resistor for two very simple reasons:

a. That is the value used in the schematic that radiance88 posted, so the assumption is that it is a "safe" value.

b. He already has that value, as it is part of the kit.

:cool:

The current that I use in LEDs: as little as possible. If it lights up well enough with 0.5mA, then that's all I use. If the requirement's
more than a few mA, then I check the datasheet to make sure the part can handle it. Usually 10mA is "safe" for the standard ones,
and 2-3mA for the miniature leaded ones.

When applying 60Hz AC voltage to an LED, the current isn't particularly straightforward. The LED only conducts on one-half cycle, and the
applied voltage is a sine wave. The average current is one-half the average of the integral of Isinx with respect to x, over the interval
from 0 to pi; where I = peak current. This gives an average current that is about 0.318 times the peak current. For a 12V(RMS) transformer
with an LED and a series 1k resistor, this should give about 5mA of average current.

BTW, does anyone know how to enter math equations in this forum? Is it possible?

IrC - 5-2-2015 at 18:11

Polverone installed Mathjax but I don't know anything about it other than it vanished my long post one day as I was writing it when he set it up. Mathjax causes my windoze 2K to reboot the moment it loads. He provided the entry I added to my hosts file which blocks it loading allowing me to still be here. So I cannot help you other than to point you in the direction of studying how to use Mathjax since your request is its purpose.

radiance88 - 6-2-2015 at 07:19

Ok. There were definitely a few things that confused me but the more I put some focus on it bit-by-bit the things seem to become a bit clearer. Still fuzzy, but there is progress.

First of all, on the enclosure, it had room for 6 adjustments, and 7 LEDs. Each was 3V, 4.5V, 6V, 7.5V, 9V, and 12V. What confused the heck out of me until recently is the 7.5 adjustment with its corresponding LED hole, which is right in the middle of the 6 and the 9. As there are only 5 taps for me to draw from, it's become obvious that the enclosure is a manufacturer screw-up, there is no 7.5V with this device (thank you China).

I also had no clue what a bridge rectifier was, but after it being mentioned here I looked it up, and now I have a developing understanding of that as well.

I've learned to use my multimeter to find the complementary pins of the switch, so that is a win for me as it's no longer a problem now. I'll try to keep your advice in mind "when in doubt, check with the multimeter".

Also the switch I have only has two pins, one hole each. So I guess that it will only connect to my negative side, right after my fuse but before my transformer? Another source of my confusion was the fact that I didn't see this on/off switch anywhere on the diagram, so I had no idea where to place it.

I also have a red LED, which also seems to need to be placed in a hole right above the power switch.. So this is our "power on" LED. It doesn't seem to be on our diagram though. Where should I connect this?

IrC - 6-2-2015 at 11:45

Quote: Originally posted by radiance88  
Also the switch I have only has two pins, one hole each. So I guess that it will only connect to my negative side, right after my fuse but before my transformer?

I also have a red LED, which also seems to need to be placed in a hole right above the power switch.. So this is our "power on" LED. It doesn't seem to be on our diagram though. Where should I connect this?


Since you only have 5 taps wire it as WGTR indicated in his schematic, CCW = 0 volts (off number 2 - output side, power switch being off number 1 - AC line input side).

There is no negative side for the AC power line. One could call the neutral such but in the interests of not giving a student more confusion to erase from the mind later when studying DC its best to stick with 'hot' and 'neutral'. As to the LED for power connect it to the 12 volt tap on the transformer, either way, get another 1K resistor, connect to other lead of LED. Other end of resistor goes to the '0' or bottom of the secondary winding. This way the LED will light when the main power switch is on no matter where the rotary is set. The AC line hot side goes through the fuse then SPST switch to the hot side of the primary, the '0' of the primary goes to the AC neutral. I do not know what service you have, am assuming USA 117 VAC. If EU or AU 220 VAC it would not matter other than being sure of your primary taps (220). In the diagram WGTR posted he is assuming your power switch is a DPDT and was merely switching both sides of the AC line at once. I am unsure what you have but if two holes I assume SPST so only switch the hot side, connect the neutral to the bottom of the primary direct.

WGTR - 6-2-2015 at 13:25

Oops. From the picture it looked like the power switch had four pins, but I suppose it was just a pair of strong shadows. In that case, add the switch right after the fuse, as you said.

This kit is not exactly for beginners. This is not because the circuit is difficult; it is actually fairly simple. It is because the schematic only offers "guidance", and assumes that you already know where everything goes. That's not very helpful, is it?

There is a reason that there is a 7.5V setting on the panel. Can you guess what it is?

Here is some "thinking outside of the box" for you: There isn't really a "0V" and a "12V" wire coming out of the transformer. In this context the important thing is that there is a 12V difference (in RMS AC voltage) between the two taps, not that one is 0V and the other is 12V. It is just as easy to flip the taps mentally, and say that the 12V tap is 0V, and the 0V tap is 12V.

What happens if we decide that our 12V tap is now the 0V tap? We end up with taps for 3V, 6V, 7.5V, 9V, and 12V. Notice that the 4.5V setting is now missing. It just depends on your preference as to how you want to wire it up. Some people might want the 7.5V setting instead of the 4.5V one.

IrC - 6-2-2015 at 13:38

Nice thinking out of the box. I did not like using the term '0' myself because it is misleading but it is already in his mind due to the labeling on top the transformer. Just figured he would see the '0' as his common and since it is marked that way on the actual transformer. Hopefully he will figure it out. I would think the 4.5 volt tap is more useful than 7.5 volt tap unless maybe one is powering a circuit on the bench which is designed for a 9 volt battery when not on the bench.

WGTR - 6-2-2015 at 13:47

I need to be a little more careful with my second-person pronouns. I was directing that info to radiance88, as I figured that this is old-hat for you, IrC!

IrC - 6-2-2015 at 15:09

I knew you were I was just adding my 2 cents to the board.

radiance88 - 6-2-2015 at 22:32

Ok, a few new concepts learnt there - when dealing with AC (as they switch direction back and forth) there is no such thing as positive and negative , and voltage is really just the difference between two potentials.

I'm curious though as to how the current flows through this circuit. I'm quite sure my current understanding of electricity is a bit flawed so let me ask a few questions: Are the capacitors and resistors essential in this circuit, and does current actually flow through them?

e.g. if there are multiple pathways for current to flow, doesn't it always choose the path of least resistance?

The following questions assume we're talking about the positive movement of our sine wave (12 volt tap actually does output 12 volts):

Couldn't the flow of electrons go from the tap, bypass the LEDs and 1K resistor by going through the connection in the middle of our switch, head to the bridge rectifier, then head out directly our positive DC end on top? And on its return route, head from the negative DC end on bottom, pass through the rectifier and head straight to our 0 tap? How did our current flow through the diodes, capacitors and resistors?

WGTR - 6-2-2015 at 23:55

I think now is a good time to introduce Ohm's Law. It is probably the most basic and important equation when starting to learn electronics. It is simply:

V=I*R, where

V= voltage (in volts), I= current (in amps), and R= resistance (in ohms)

Using simple algebra, the equation can be rearranged. In other words, R=V/I, and I=V/R.

If you have a 9V battery, and you put a 1,000 ohm resistor across it, 0.009A of current flows through the resistor. Also, if you have a 100 ohm resistor, and you measure 0.01A flowing through it with the meter, then that means there is 1V across the resistor. Try verifying these things with your meter, and see if this equation makes sense to you.

A resistor resists the flow of electricity. Technically, everything has some resistance, even copper wire. Resistors, however, are designed to have a specific amount of it. The resistance can be measured with your multimeter, or the value of a resistor can be determined by the resistor color-code that I posted earlier. Using a resistor, you can control the amount of current that flows in a particular part of the circuit.
Quote:
Ok, a few new concepts learnt there - when dealing with AC (as they switch direction back and forth) there is no such thing as positive and negative , and voltage is really just the difference between two potentials.


Yes, sort of...another way to say it is that voltage is relative. In most circuits, we pick one part of the circuit to be the common, or ground. This part of the circuit is considered to be 0V. Everything other voltage in the circuit is compared against that.

Since a transformer outputs an alternating voltage, its average voltage equals zero. In this way you are right that there is no net positive or negative voltage output.
Quote:
I'm curious though as to how the current flows through this circuit. I'm quite sure my current understanding of electricity is a bit flawed so let me ask a few questions: Are the capacitors and resistors essential in this circuit, and does current actually flow through them?

e.g. if there are multiple pathways for current to flow, doesn't it always choose the path of least resistance?

The following questions assume we're talking about the positive movement of our sine wave (12 volt tap actually does output 12 volts):

Couldn't the flow of electrons go from the tap, bypass the LEDs and 1K resistor by going through the connection in the middle of our switch, head to the bridge rectifier, then head out directly our positive DC end on top? And on its return route, head from the negative DC end on bottom, pass through the rectifier and head straight to our 0 tap? How did our current flow through the diodes, capacitors and resistors?


To answer your first question, yes, current flows through all of the components in one way or another, and to varying degrees. They all perform specific functions in the circuit. The circuit would operate differently if any of them were removed.

Ohm's Law answers your next question. If there are two parallel paths for current to flow, then more current will flow in the path with the least resistance. One path doesn't hog all of the current, though, unless that path happens to be a short circuit (0 ohms).

Capacitors are like miniature batteries. They are actually quite different from batteries, but this is a generalization. They are placed on the output of the power supply to smooth out the output from the bridge rectifier. You know how the transformer puts out an AC wave? The bridge rectifier folds over the AC voltage so that both halves of the AC voltage have the same polarity. While this gives a positive output voltage (in this circuit), it is still a very noisy voltage, since it is a rectified AC voltage. The capacitors try to smooth out this noise, and supply smooth DC voltage at the output.

I have to go to bed now, but to answer your last question, the LEDs don't get bypassed unless you tie a wire directly from the output to ground, i.e., you short out the output. At this point the fuse would blow (hopefully). Once the capacitors charge up, they look like an open circuit, so they do not short out the output.

Zombie - 7-2-2015 at 00:03

Think of it this way. A diode is a one way passage. Any power will only flow in one direction thru it. A rectifier is a group of diodes to change back, and forth flow (AC) into one direction flow (DC).
A resistor is just like a knot in a hose. It only allows a set amount of power to flow thru. The more "resistance" the lower the flow. It also does it's job in both directions so it can pass both AC, and DC current.
A capacitor is like a bicycle ramp. Current has to jump across a gap to reach the other side. It will only allow a set current just like a ramp will only allow you to cross if you have enough speed.Too fast, and you know to slow down. too slow, and you know to speed up.
That ties into the phrase Sine Wave. That is neither current or voltage. That is like the pedals on the bike. It is the frequency of the power or the up, and down movement of the pedals. Capacitors allow a set amount of up, and down movement to pass, while blocking the movement that will not work. Just like the ramp.

Did you notice how all of this is just like water flowing? Least resistance is correct. Start at the source, and follow the flow.
IF your LED does not light... Where do you look first? The source!!! Start at the wall outlet. Go to the next place... The switch then at the transformer, It flows like water. It changes pressure, and flow rates but it MUST follow the path you set up for it.
When it doesn't? start at the source.

I hope this is helpful. The fellas here want to teach you the correct way of learning this. I want to make it easier for you to see in your head what is happening.;)

I Like Dots - 7-2-2015 at 06:06

Hey guys, quick heads up. Radioshacks across america are going out of business, which means they are having HUGE closeout sales on electronics. I got a grab back of components (resistors, diodes, fuses, led... etc) valued at $500 for $3. I also got This kit (and number 2) for only $4. I also picked up a ton of Arduino peripherals for like 90% off!!!

Magpie - 7-2-2015 at 10:28

I'm going to ramble/rant a bit here.

Ramble: You can assemble an electronics circuit by following someone elses schematic and it should work as advertised. And this is a perfectly acceptable way to begin learning. But to truly learn how an electronic circuit works you must learn how the basic components of the circuit function, ie, resistors, capacitors, inductors, transformers, wires, batteries, generators, etc. In fact, if you just learn about resistors, capacitors, and inductors you will have taken a giant leap and gained a solid foundation. This all will take time: take it one step at a time, and enjoy your latest victory in comprehension. Don't expect to learn this overnight! ;)

Now, to really understand these concepts you must have some math skills. Basic algebra is a must. This will allow you to manipulate Ohm's Law, understand current flow through parallel resistance paths, etc. Understand a sine wave (trigonometry) and then you can move on to AC circuits. I recommend mastering DC circuits first, by all means - they are much simpler.

Electronics is like math: you build on the basics, giving you a solid foundation. If you try to jump into something without understanding the basics you are screwed as far as having a true understanding.

Rant: The demise of RadioShack is a true catastrophe. Where else will I be able to drive to a nearby shopping center and buy electronic components. Some of the clerks (though not many) even understand electronics! Fortunately for me only 1 of my 2 stores is going to close. The remaining one will likely become a smarmy Sprint, only interested in selling consumer gadgetry. Then they might well get rid of their component drawers altogether. :( I hope not.

IrC - 7-2-2015 at 11:20

"The remaining one will likely become a smarmy Sprint, only interested in selling consumer gadgetry. Then they might well get rid of their component drawers altogether."

After they accomplished the demise of Lafayette (vastly superior in component product line for experimenters) they started this trend (doubling or more all prices compared to the competitors they destroyed) from the early 80's on, and this idiotic business model is exactly what did them in. I asked a suit in Tandy Corporate one day in the 90's why they kept discontinuing every single item so much in demand by people like myself. He explained all marketing decisions were based upon sales numbers at a single company store in downtown Manhattan. He even agreed with my point that people there were not an example of hobbyists in the rest of the country. Sad that the decision makers were not interested in sound business practices.

woelen - 7-2-2015 at 13:19

What happens to Radioshack in the USA now already happened 10 years ago where I live. At that time, there were three electronics shops in the city where I live and you could buy resistors, capacitors, many types of semiconductors, many types of integrated circuits and also all kind of equipment and kits. Nowadays we only have one electronics shop left and they are mostly sell complete devices and gadgets. You can buy some basic electronic parts (e.g. resistors from the E12 series, 0.25W and a few somewhat larger power resistors, some capacitors, some LEDs and some types of wires, clamps and so on), but all of the specialist components are gone. For me, the only serious source of electronic components is the internet (e.g. eBay).

This is a general trend. The big shopping centers carry less and less specialist stuff. Clothes, mobile phones, standard consumer electronics and a lot of perfume, cosmetics, life style products. The special hobby, arts and electronics shops are gone :( 10 years ago already.

Zombie - 8-2-2015 at 02:04

Same here. I have not seen or been in a proper electronics shop in at least 10 years. All of the Radio Shacks were sold as franchise stores years ago.
They are mainly cell phone chargers, and as Woelen said, gadgets.

Everything I use comes off the net or catalogs.

[Edited on 8-2-2015 by Zombie]

radiance88 - 8-2-2015 at 05:34

Ok WGTR - I performed both of the tests you instructed me to earlier in the thread. I don't have a 9 volt battery lying around, so instead I used the 9 volt tap. I constructed the circuit on my breadboard (to the best of my knowledge), and more or less it seems to work.

I'm not so sure about the results of these tests though.



At 9 volts AC input, testing for voltage at the DC ends on the other side of the rectifier gives me 11.12 volts. Same amount is obtained by flipping my two AC wires.

At the same 9 volts, measuring for current with my multimeter gives me .07 millivolts/.7 microvolts either way. I measured twice with both my milli and micro settings to make sure that it wasn't screwing with me.

Somehow these don't seem to add up to your original estimates of 7.5V output voltage, and 7-8 millivolts. I thought since the current was off a couple of decimal places that there was something wrong with the resistor, and so I checked it, but it gave me a very close cut to the rated 1000 ohms, so the resistor seems to work fine.

I must be doing something wrong here?

[Edited on 8-2-2015 by radiance88]

Fulmen - 8-2-2015 at 06:36

Have we covered RMS yet? It is basically the "average" or more correctly the equivalent DC voltage, meaning that a 9V RMS AC will produce the same power as 9V DC.
The reason for not using "average" is that since AC fluctuates between positive and negative the average voltage will be zero. But since power depends on the magnitude of the current and not the direction an average of zero can still produce power.

The peak voltage will be higher than the RMS by a factor of 1.4 (square root of 2), for 9V this will be 12.7V. But since the current passes through two diodes the peak voltage after the rectifier will be slightly lower, ~11V sounds about right.
You also have to take voltage drops in a transformer into account. Since voltage drops with current (U=R*I) the output voltage is usually chosen for a given load, below this load the voltage will be slightly higher. The actual mains voltage also fluctuates, all this makes transformers inherently imprecise voltage sources.

WGTR - 8-2-2015 at 10:31

1. The circuit looks good. The diodes look like they are pointed the right way, and the capacitors are the correct polarity. Also, I see the 1k resistor on the output.

2. I made an assumption that your meter can measure current. Current is measured in amps (or milliamps,microamps,etc.), not volts. Would you mind posting a picture of the meter; something close enough that we can read the settings on the front?

3. I suggested a 9V battery, because the measurements are simpler that way. If you want to use the 9VAC tap, then Fulmen is right. 9VAC is not exactly the same as 9VDC. Imagine that you had an oscilloscope for a moment. When looking at 9VAC on the display, you would see that the voltage actually swings up to a maximum of 12.7V+, and then down to 12.7V- when it reverses polarity. This delivers a 25.4 peak-to-peak voltage. If you run this voltage through your bridge rectifier, the negative peaks get converted to positive ones, and the peak-to-peak voltage of 25.4V gets converted to a peak voltage of 12.7VDC.

A diode only allows current to flow in one direction, as you may already know, but a diode is not a perfect device. Even when current is flowing through it, there is always a voltage drop across it. This voltage varies depending on the diode, but is usually 0.6 to 1.0V per diode. What this means, is that your 12.7V ends up being the 11.1V that you measured. For example, 12.7V - 0.8V - 0.8V = 11.1V.

Your voltage measurement of 11.1V looks correct. The only thing that I see wrong is the current measurement, because you tried measuring it in voltage instead of current (there is a way to measure it that way, using Ohm's Law, but that is "Plan B"). Also, the current at that point is AC, so you would have to measure it with an AC current setting.

So the burning question is, why is 9VAC actually 12.7Vpeak? The reason is that the power company charges you only for the energy that you use (as a "residential" user), and not for the voltage or the current. If you apply 9VDC across a 1k resistor, it heats the resistor exactly the same amount as if 25.4VACpeak-to-peak where applied across the resistor. In other words, 9V is the root mean square value of 25.4VACpeak-to-peak. Are you thoroughly confused yet?

radiance88 - 9-2-2015 at 01:34

Sorry, my bad. I meant . 07 milliamps and .7 microamps as my readings via the AC current reading on my multimeter, not volts. I got my units mixed up.

Is this supposed to be another thing associated with rectified voltage? because it really isn't anything close to what you gave me. .

Fulmen - 9-2-2015 at 01:42

What exactly are you measuring? the current through the circuit with the led shining? Make a sketch of the circuit and point to exactly where you are measuring.

radiance88 - 9-2-2015 at 04:47

The lower part of the diagram constructed by WGTR in the beginning of the thread.

diagram

My breadboard in the previous post is my replication of this schematic. Notice that there is a red wire and a white wire which aren't connected to the board - that's where I put my multimeter leads towards and measured with the millamp and then microamp settings.

AC and DC seem to be very different critters. I might as well just go ahead and finish the circuit, build it in the box and be done with it until my self-study allows me to understand a bit more what's going on.

Fulmen - 9-2-2015 at 08:50

Well, something is off. 0.07mA is the same as 70uA, not 0.7uA. You should get the same value regardless off the range, are you sure you've connected the multimeter correctly? Perhaps a pic of the meter?

AC vs DC? Yes, there are some significant differences to take into account. For a resistor it doesn't matter, RMS AC and DC gives the same (RMS) current. But since you flip polarity and current direction continuously a lot of components behave fundamentally different.

Magpie - 9-2-2015 at 09:14

Quote: Originally posted by radiance88  

AC and DC seem to be very different critters.


Yes, very much so in many ways. With normal DC circuits everything (current, voltage drops, power dissipation, etc) remain the same with time, ie, are at a steady state. With AC everything changes (in cycles) with time, at least on an instantaneous basis. If the power supply is US household 120VAC, 60 Hz, then the cycles are happening 60 times/second!

Earlier I said that understanding 3 fundamental components: resistors, capacitors, and inductors would be an important step. This is true, but capacitors and inductors normally only come into play when using AC. DC usually only deals with resistors.

A capacitor never really passes current, it only builds or stores charge (electrons). Placing a capacitor in a DC circuit having a steady voltage source is useless. It just forms an open circuit. Ie, no current will flow.

An inductors passes current but if the current is changing it causes a form of resistance to this change.
Quote: Originally posted by radiance88  

I might as well just go ahead and finish the circuit, build it in the box and be done with it until my self-study allows me to understand a bit more what's going on.


Sounds like a good plan. There's only so much you can learn by assembly alone. Alternating this with tutorials on electrical theory is a good strategy, IMO.

[Edited on 9-2-2015 by Magpie]

[Edited on 9-2-2015 by Magpie]

[Edited on 9-2-2015 by Magpie]

Fulmen - 9-2-2015 at 09:56

Quote: Originally posted by Magpie  
capacitors and inductors normally only come into play when using AC

I must object to this, especially capacitors are commonplace and indeed crucial to DC circuits. How would you build something like a multivibrator without a capacitor?
Inductors are less common in DC operations, but they still have a wide range of uses.

Magpie - 9-2-2015 at 09:59

That's why I used the qualifier normally. I'm trying to explain these concepts at a fundamental level without writing a book.

radiance88 - 9-2-2015 at 10:47

This first pic is my replication of the lower diagram, leads hooked to the "hot side" with the multimeter set at its mA, AC setting. The second is the uA setting.






I'm not really sure what to say. If my multimeter is defective then that also leaves me screwed, as I'm pretty sure I'm out of scope of the store return policy. If we can't figure this one out, I'll just build the circuit, place it its pretty box and leave this be.

Fulmen - 9-2-2015 at 10:55

I still maintain it's wrong and misleading. Now I'll agree that capacitors isn't the first ting one should focus on, but you won't get far in the world of DC without understanding capacitors. I also think one should be familiar with capacitors in a DC setting before looking at how they behave in AC.

alive&kickin - 9-2-2015 at 11:38

radiance88, since you are just starting with electronics, I have some LEDs and 8 segment displays that I can send you if you're in the states and interested. I'll be more than happy to send you a couple dozen to play with. I posted it over in apparatus acquisition and just U2U me with the address to send them to. This goes for anyone else who may be interested as I have about 30 8 segment displays and about 1000 LEDs, all brand new and free for the asking.

Magpie - 9-2-2015 at 14:18

Quote: Originally posted by Fulmen  
I still maintain it's wrong and misleading. Now I'll agree that capacitors isn't the first ting one should focus on, but you won't get far in the world of DC without understanding capacitors. I also think one should be familiar with capacitors in a DC setting before looking at how they behave in AC.


I understand where you are coming from. I'll explain where I'm coming from:

I learned about electricity in a basic electrical engineering course in my junior year in college (1963). The text we used was "Basic Electrical Engineering" by Fitzgerald and Higginbotham, 2nd ed (1957). The first chapter, "D-C Circuits" consisted of 29 pages covering "Basic Electrical Quantities," "Electrical Circuit Constants," "Resistance; "Ohm's Law," "Fundamental Circuit Laws; Kirchoff's Laws," "D-C Circuits," "More Complex D-C Circuits," "Network Simplification," "Principles of Superposition," and "Thevenin's Theorem." It was not until Chapter 2, "Alternating Currents and Voltages" the 10th page in, after describing sinusoidal voltage and current, did the book introduce capacitance.

That's why I don't naturally think of capacitors as part of a DC circuit. But, as you say, they are certainly necessary for many circuits powered by DC voltage.

But once you start chopping and making the voltage pulses non-steady state (cyclic transients) do you really have a DC circuit anymore?

Fulmen - 9-2-2015 at 14:25

Yes. Alternating currents implies a reversal of flow. One can always subdivide DC into steady and non-steady state, and your statement does make a lot more sense in that context. In a steady state circuit a capacitor has little use.

WGTR - 9-2-2015 at 14:48

Quote: Originally posted by radiance88  
I'm not really sure what to say. If my multimeter is defective then that also leaves me screwed, as I'm pretty sure I'm out of scope of the store return policy. If we can't figure this one out, I'll just build the circuit, place it its pretty box and leave this be.


Both readings are near the bottom of their respective scales, and the accuracy may be rather poor at that point. What happens if you unplug the transformer with the meter still connected in the circuit? Do the values change, or stay where they are?

I have, on more than one occasion, accidentally tried to measure voltage while the meter was set up to measure current. What happens at this point, is that a lot of current will try to flow through the meter. This blows the protection fuse inside the meter. The voltage measurements are still good, but the meter will not measure current until the fuse is replaced. Sometimes, there is an extra fuse inside the cover, because everyone makes this mistake at some point. Just popping the cover off the back of the meter and looking at the fuse should tell you if this is the problem. Heck, you can even take the fuse out and check it with your ohmmeter. It should be almost 0 ohms.

The only other thing I can think of, is that perhaps one-half of the bridge circuit is not making a good connection. You could try measuring DC current to see if you get a stable reading.


[Edited on 2-9-2015 by WGTR]

IrC - 9-2-2015 at 18:10

"multimeter is defective then that also leaves me screwed"

Either I am not understanding your circuit or your meter was fine until you connected the meter across the rail in a current setting. Very bad idea. As magpie suggested go look at your fuse. I am assuming the red and black banana jacks are your plus and minus rail? If so why are the meter leads on them with the DVM clearly on a current scale? Only measure voltage in such circumstances, always put the meter in series with the circuit when measuring current. Second, on the first couple pages of this thread links to very good sites with great tutorials were posted. With this in mind why are you still asking simple questions (covered in depth in the links provided) instead of spending at least some time studying in lieu of asking people here to take time answering? Hopefully I am not coming off too negative here but there is a point at which one would begin to wonder if you are taking any time to study on your own.

Concerning capacitors and some comments by magpie and fulmen two things; even in a so called steady state circuit capacitors have use. For example a 7808 regulating from a 12 volt source, capacitors here prevent oscillation of the regulator even though we have a steady 12 volts in and a steady 8 volts out. Also in many other circuits whether to prevent oscillation or to reduce the noise on the rail. Other examples apply as well. Second, even in a fairly steady state circuit, say a medium to long duration timer, a capacitor charging slowly provides a time reference. Depending upon the time frame being considered one could say the circuit was 'steady state'. I am kind of with magpie on the learning in the AC section of the book for similar reasons as he. I'm old and my learning started with the same and similar books. Notwithstanding capacitors are important to understand even in the beginning with DC theory for many reasons, a couple of which I just discussed.

WGTR - 9-2-2015 at 19:57

IrC, he had the meter in series with the bridge (to measure input current), so there shouldn't be a problem with that measurement configuration.

I don't mind answering questions as I have time. When I first started out, I bothered people incessantly with dumb questions. They were quite patient with me. Even with books, it took me several years to figure out the transistor. Since transistors "amplify", at first I thought that meant they created their own energy. I envisioned building a car powered by thousands of transistors. Around this time I dreamed up an electric motor that would supply its own power by turning a geared-up generator. I tried explaining this concept to a relative of mine (who is an engineer). He kept trying to explain to me why it wouldn't work, and I kept thinking that he didn't understanding what I was trying to do. After all, it was obvious to me that the idea would work. At the age of 11, I had a creative imagination, but I was as dumb as a box of rocks.

Once I figured out the purpose of the transistor, I labored ineffectively at trying to get one to amplify something. Either I messed up the biasing, or I hooked the transistor up backwards, or had bad parts...I don't know, but somehow it took me several years of frustrated tinkering before I finally figured it out. Vacuum tubes were the only thing I could get to work during that time. An older friend of mine was befuddled by my difficulties. After all, transistor biasing was the easiest thing in the world to him. Had someone sat down with me and built a transistor circuit with me, walking me through the design process, showing me that transistors do in fact "work", it would have helped an awful lot.

Anyway, I don't mind walking someone through their first circuit. It's usually that first circuit that determines how one looks at electronics going forward.

IrC - 9-2-2015 at 22:26

Had to study the images real close, no depth in 2D. I see your point the black lead is slightly above the post hooked to a wire to the top of the bridge. But I do not see where the bottom of the bridge (AC side) goes back to the other transformer winding. One side goes to the red lead through the meter back to the bridge. Is the other winding connected?

I realize you like helping him so do I but I thought it good to prod him into spending time studying the tutorials (and the math) in the links.
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