Sciencemadness Discussion Board - looking for DACS strip chart recorder software

looking for DACS strip chart recorder software

SHADYCHASE54 - 11-1-2018 at 19:39

Hello all, I am wondering if anyone can point me in the direction of a link to open source DACS strip chart recorder software. If free isn't possible I can afford 100-$200 at most for the software the program is for an old Gow Mac 350. Please any help on this topic would be appreciated.

NEMO-Chemistry - 13-1-2018 at 04:12

Do you mean one of those pen charts?

SHADYCHASE54 - 13-1-2018 at 07:39

Actually the pen chart recorder is what I would like to avoid. I am attempting to determine a means to digitize the recorder and run the system through computer rather than finding a pen cart recorder. I know this is possible, compatible software exists however finding what could be considered antiquated software has proven frustrating. The software I have found are sadly incompatible apparently to advanced. Found one that was compatible with Gow Mac 580 or something something similar however I am running a 350 and cannot risk the $$$ on the hope that it might function. If anyone can offer sage advice please do I implore you.

Thanks.

NEMO-Chemistry - 13-1-2018 at 07:59

Quote: Originally posted by SHADYCHASE54

Actually the pen chart recorder is what I would like to avoid. I am attempting to determine a means to digitize the recorder and run the system through computer rather than finding a pen cart recorder. I know this is possible, compatible software exists however finding what could be considered antiquated software has proven frustrating. The software I have found are sadly incompatible apparently to advanced. Found one that was compatible with Gow Mac 580 or something something similar however I am running a 350 and cannot risk the $$$ on the hope that it might function. If anyone can offer sage advice please do I implore you.

Thanks.

Maybe its me being stupid, or maybe your shit at explaining.
Lets start again....

I assume you have some kind of device, maybe something like a data logger? What is the make and model of this device? What does it do?

Or you have software and no device. Or you just want some software that does something?

NEMO-Chemistry - 13-1-2018 at 08:04

As a rule of thumb, anything that normally connects to a chart recorder can easilly be interfaced to a variety of software. This is not normally expensive, unless you want specific software. Or put another way, you have your heart set on a pirate copy of software and wont consider using any other software.

Pen charts are analog, so interfacing to a computer is easy via a Arduino or other micro controller and a £2 cable.
From there you can then use some shit like visual basic and build your own software, or better yet use Matlab and labview to do really cool shit, or normally we can find software to do what you want.

Crowfjord - 13-1-2018 at 09:12

Labview is a good one, though I suppose it isn't open source. I used it in my undergrad research to chart the output of a cyclic voltameter. I can't remember what I used for the analog to digital interface, though.

[Edited on 13-1-2018 by Crowfjord]

NEMO-Chemistry - 13-1-2018 at 09:28

Quote: Originally posted by Crowfjord

Labview is a good one, though I suppose it isn't open source. I used it in my undergrad research to chart the output of a cyclic voltameter. I can't remember what I used for the analog to digital interface, though.

[Edited on 13-1-2018 by Crowfjord]

I think you can get a student version or a free type version. I am not sure, i have the student one. I also think you can get a similar software that is open source.

But depends what you want to do, i assume its draw a graph. You could just import a CSV file into excell and have a macro do it.
As for the interface thats the easy bit.

A simple £5 Arduino board and £2 cable will sort that, use a rsr232 to USB cable, connect device to the ADC pins on the micro and use the RS232 peripheral in the micro to output the data as serial over the cable.

Something like xterm could pick that up and record to a CSV file.

with more details i could prob sort something easy enough

SHADYCHASE54 - 13-1-2018 at 12:41

Thank you for the explanation regarding interfacing a Gow-Mac 350 gas chromatograph from analog ports to a digital port. What I am hoping to find is a windows compatible program to chart and measure the compounds' abundance as they leave the column. I have some experience with TLC however no experience with GC as such the equipment is new to me and I expect a moderate learning curve. So thank you again for any advice you can or already have provided. I am presently looking into Matlab and Labview to see if they will work out for me.

Crowfjord - 13-1-2018 at 14:10

Once you get your output converted and graphed, you will then need to calculate the area under the curves to determine amounts present in the sample analyzed. Some calculus will be required if the equation for the curve can be figured out, or more simply, the trapezoidal approximation using the raw data. This is what I used in school to quantitate caffeine in drinks via GC-FID years ago.

SHADYCHASE54 - 14-1-2018 at 22:20

Quote: Originally posted by SHADYCHASE54

Hello again I decided I wasn't being very clear with my request as I hadn't time to really think about it. I have an old Gow Mac 350 gas chromatograph. I need to convert the analog output to 24bit digital. Now that I have looked into this a little more I realize I do not simply want chart recording capabilities I would like all the analytic bells and whistles that can be had for GC chart recording as well as analysis. I have bought a book on hacking ardino so hopefully this will help me with the a/d converter any further advice pertaining to the project of getting this basic GC operational would be appreciated.

[Edited on 15-1-2018 by SHADYCHASE54]

NEMO-Chemistry - 15-1-2018 at 04:05

I need to think on this, there is an interface unit used for scientific equipment, it has 6 ports. in essence all it does is take serial data from the machine, and converts it into a format for the software.

They are not expensive, then again what they do isnt hard.
You should be able to get hold of a copy of total chrom software by elmer perkins. That will give you all the info you need and graph everything and then some.

The output from your machine draws a graph, it simply outputs a voltage that a graph recorder then uses. This is no different to any other GC. Except most newer ones then send the data as RS232 or similar.

I am positive you dont need 24bit data, no pen recorder could use data approaching that kind of resolution. A 10 bit ADC is more than good enough. thats 1024 resolution. What is the max voltage output on the back?

I still see no reason why you couldnt sample the output with a micro, then just have the micro send out the data in serial format. Total chrom would look for a serial port, this is where the USB cable i spoke of comes into play.

The cable sets up a serial port via USB, so you would map the software to that port, the only real problems you have are as follows

1) What is the mx peak voltage the pen chart sockets output?

2) What kind of speed does it do it at?

You would normally set the pen chart for X cm per min, this is the speed that the GC outputs the data. To convert it, you really need to run a sample and connect an oscilloscope to the output. That would tell you everything you need to know.

I would mix a couple of solvents up and run them, then sit and watch the scope for the peaks. From that you would get a good idea what to set the serial baud rate too.
Also it would let you know what kind of resolution you need. None of this is hard, but all of it is impossible without information.

I will go see what info i can find on your machine, but 100% for sure, if it outputs to a pen chart, then you can interface it to something like total chrom Gas chromatography software, that basically acts like a digital pen recorder, but it can work out the area ect etc etc. All the bells and whistles you want.

SHADYCHASE54 - 29-1-2018 at 20:55

NEMO-chemistry I have a quick question do you think this would work as an adc for my old GC?
https://www.dataq.com/products/di-1100/

NEMO-Chemistry - 30-1-2018 at 06:29

no thats over complicated and i think the wrong voltage

EDIT
Sorry there is two GD threads on the go!

I dont know, I need a day or so to look up the data sheets etc. Give me a couple of days and I will see what I can find as a cheap bolt on for you

[Edited on 30-1-2018 by NEMO-Chemistry]

NEMO-Chemistry - 30-1-2018 at 06:38

Do you have a pen recorder for it?
If you do what voltage settings do you use?

if you dont can you kind of run a sample?
If you can kind of run a sample do you have a Multi Meter?
If you do can you run a sample, stick the multi meter on the out puts. IF your multi meter has min-max setting to capture min and max voltage, use that. if it dosnt sit and watch, record the max output voltage.

Honestly with a little work I am 100% sure you can do this for under $20. I am also 99% sure you can plonk the data into the computer and have it do all the grunt work and calcs you need, price range from free to whatever what to spend.

But honestly if it can work a pen recorder then it can be done cheaply and it can be done well.
If you can solder great, if you cant then we can get around that. Dont worry about code etc....... Thats easy to get or do.

SHADYCHASE54 - 30-1-2018 at 08:01

I would firstly like to say thank you for sticking with me on this project. Unfortunately I don't have a pen chart recorder so I guess that leaves me with option 2 running a sample I am going to have to transfer my new argon cylinder into an old CO2 cylinder so that I can refill with helium, as it is the only carrier to be used with this model. Meaning it will take me a bit to order the proper transfer valves. I have been hesitant making an ADC via Arduino as I am a little intimidated with the coding requirements. Regardless I will be ordering both the Arduino mini ➕ Uno, breadboard kit. For the actual a/d converter should I also order something like an ads1015 12bit ADC? Again many thanks for your help.

Attachment: breton2000[1].pdf (16kB)
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wg48 - 30-1-2018 at 09:46

Quote: Originally posted by SHADYCHASE54

I would firstly like to say thank you for sticking with me on this project. Unfortunately I don't have a pen chart recorder so I guess that leaves me with option 2 running a sample I am going to have to transfer my new argon cylinder into an old CO2 cylinder so that I can refill with helium, as it is the only carrier to be used with this model. Meaning it will take me a bit to order the proper transfer valves. I have been hesitant making an ADC via Arduino as I am a little intimidated with the coding requirements. Regardless I will be ordering both the Arduino mini ➕ Uno, breadboard kit. For the actual a/d converter should I also order something like an ads1015 12bit ADC? Again many thanks for your help.

Why not use an ADC card for your PC. You may be able to get a USB one these days. Check on ebay.

SHADYCHASE54 - 30-1-2018 at 10:17

NEMO-. I uploaded a PDF that may fill in some holes.

Wg48 thank you for your suggestion however I am extremely unsure of my ability to find the proper ADC PC card install and format for whichever GC charting software I settle on.

NEMO-Chemistry - 30-1-2018 at 13:05

Quote: Originally posted by wg48

Quote: Originally posted by SHADYCHASE54

Why not use an ADC card for your PC. You may be able to get a USB one these days. Check on ebay.

For this project the card would cost too much and they are restrictive, an arduino cuts out alot of problems including drivers.

It uses a rs232 to usb cable that costs $2-$3.

The code is the least of the problems, the net is full of code that will do it.

Actually the arduino is simply a go between, its only function is read the voltage and spit it out in serial format, in code terms this is 3 hours from never seeing an arduino to learning how to program it to that!

But we wont be cruel, we can sort the code for you, its roughly 30-60 mins work tops.

Dont get the gas yet, i will track down some info, if you got any idea of a manual or what kind of pen plotter, then I can start working out the voltage.

The more I learn about this, the more I am sure this is $10-$20 project tops including pc software that will do anything you want.

I need some time purely because I am busy, the other reason you dont get a pc card is safety for the pc. These old machines are better off directly connected to a special cheap cable.

ANYTHING at all that out puts to a pen chart, simply needs a bog standard 10 bit ADC capable micro. Once we know the max out put voltage I can sort a resistor divider and maybe if needed a opamp for you.

I doubt you will need the opamp though.

Oh and zero need for thanks, i will stick with it for as long as I can help. So far i am pretty convinced this should be nice and easy. I have had immense amounts of help from this site, so dont thank me, its just real nice to be able to give a little back.

[Edited on 30-1-2018 by NEMO-Chemistry]

NEMO-Chemistry - 30-1-2018 at 13:14

Just read the PDF
You will need a opamp, but the good news is you will get great resolution. My fear was the output would be above the arduino handling level, if it was me I would go pic micro route. Simply because I prefer them and they are native 5V.

Arduino will be fine, the opamp is simply to increase the output voltage to a level where the arduino can deal with it easily. It sounds complicated to you, but its not, and it falls into the simple to guide someone catergory.

paying $100 for a ADC data aq is stupid for this. simple arduino and cable and mic in matlab or labview and you have a system that can do anything you likely to throw at it.

wg48 - 30-1-2018 at 13:21

OK then how about a USB digital scope then. Comes with the drive and display/storage software for £20

https://www.ebay.co.uk/itm/iCP12-5mV-u-6-Ch-PC-Analog-USB-Os...

NEMO-Chemistry - 30-1-2018 at 17:03

Quote: Originally posted by wg48

OK then how about a USB digital scope then. Comes with the drive and display/storage software for £20

https://www.ebay.co.uk/itm/iCP12-5mV-u-6-Ch-PC-Analog-USB-Os...

The main difference is he wants to work out peak area etc, using the arduino and serial to usb cable, you can transfer the data live straight into 'normal' GC software or matlab.

That way you get alot of the modern function and capabilities of a GC. OK you cant operate the machine remotely etc, but you can use all the GC software to do with the output.

Plus those scope cards are not great TBH, i am biased as i have a real scope, but this is honestly a very simple analogue to digital conversion, then simple serial data streaming of it.

The serial to usb cables are so cheap, they also emulate a serial comm port, so alot of specific GC software would then work with the trace. With a scope card you get the data on the screen but then you got a headache with memory depth and area calculation etc.

But its the OP's choice. I will look into it for him, the fact he has to use helium and yet has a very short column.... i think the problem is going to be separation of peaks, again this is where an arduino wins. You can alter sample rates etc as much as you want. most scopes need the vendor software and driver.

The other way dosnt need a driver (apart from the normal usb HID one).

£20 is a rip off! But it is a decent pic micro in it, the 1mV resolution might be an issue, might!

But if the OP was comfortable with programing in C, then actually that is the kind of micro I would go with. But I would use a instrument rail to rail opamp with it.

Its a great chip that pic, but ideally you would want the bare chip and no code on it. Then we get into having to code in C and....

In this case arduino is just the simple cheap option.

I will check......But I dont remember that particular cip having a 12bit ADC, I thought all 18f series had 10 bit.

EDIT
Only had a quick read of the data sheet, AND checked the errata, seems the chip is capable of 12bit ADC.

I will look into it more, it might be a way around. But depends how locked down it is, dont get me wrong, that chip would do a grand job, the question is will the way they have configured it, work with the software we have in mind.

I will get back to you.

[Edited on 31-1-2018 by NEMO-Chemistry]

[Edited on 31-1-2018 by NEMO-Chemistry]

SHADYCHASE54 - 30-1-2018 at 21:23

I purchased the ardunio uno and a mini, ADC chip ads 1115\1015, a rs232 cable and a non solder breadboard kit. God knows how long shipping will take? If you can think of anything else I should get feel free to tell me and I'll get on it right away. To this point it has cost me only $19.00 which isn't an issue as I doubt this will be my last adunio project; the more I read about the possibilities the more exciting it all seems. I am reading a book I bought, "Hacking Electronics" by Simon Monk, just began reading hopefully it will give me a little insight into the topic so that once I begin the project I should have at least an elementary understanding of reading circuit diagrams and some Arduino capabilities. Again thanks for all relevant information provided.

wg48 - 31-1-2018 at 04:09

The adavantage of the USB scope is its ready to go without any additional software other than its own. You would be able to view your graphs and store them its different formates. Its also not limited by its own memory if used in logging mode.

Ineffect its a digital pen recorder. The major problem with it is its very limited common mode rejection. As Nemo suggsted it needs a better front end to improve that.

As to how compatible its file formates are with other software you may use I do not know. I guessing that the files could be read by Mathcad, Matlab and Simulink with little if any processing.

NEMO-Chemistry - 31-1-2018 at 05:15

Quote: Originally posted by wg48

The adavantage of the USB scope is its ready to go without any additional software other than its own. You would be able to view your graphs and store them its different formates. Its also not limited by its own memory if used in logging mode.

Ineffect its a digital pen recorder. The major problem with it is its very limited common mode rejection. As Nemo suggsted it needs a better front end to improve that.

As to how compatible its file formates are with other software you may use I do not know. I guessing that the files could be read by Mathcad, Matlab and Simulink with little if any processing.

I havnt used that software before, but i have used alot of pics. The main issue you are going to face is ref voltage. The picture isnt great but i couldnt see a dedicated voltage reference, so i am assuming the ADC is set to use the internal ref, this is ok normally.

However in this particular case your dealing with mV, when you consider the swing you normally get with any power supply, I start to have doubts.

But the biggest problem is the front end software, What I have in mind is for you to use Total Chrom by elmer perkins, this is industry standard Gas Chromatograph software, done with serial input, it becomes native.

There is no interface or file faffing, inside total chrom is a set up section, you simply pic the com port, the com port is set up by the serial to usb cable, so you dont have to mess with any file conversion.

I do like the pic in the scope, but I think its likely they have set the code in a manner that will frustrate you. But we will keep it as an option.

The big problem is actually your GC, your column is really short, most columns these days are over 30M. The fact you have to use Helium says to me the detector has awful pickup.

So your going to be limited by the machine and its capabilities, but keep in mind the options that you started looking at, these are all expensive and contain features your never going to use.

I wont run through the features of total chrom, but its designed by the second best GC manufacture, and some people who use the best GC company for the GC itself, actually use elmers software to run it.

Dont worry about time to get there, your going to need a half decent multi meter for this project, the opamp you might be able to get as a sample. I would suggest we look at a 100x signal boost, i doubt you will need more.

With the arduino I can alter the code if we need to over sample, so in summary.

The scope thing, I would have jumped at the bare chip in other circumstances, i wouldnt touch the scope version as I dont know what code access if any you will get.

Pics are not beginners chips like an arduino is, the world and his wife,dog can code. Its 32 bit and not 8 bit like the pic. I am talking about the actual chip not the ADC on it.

Personal opinion of mine is, you dont try and use a 12 bit ADC on a 8 bit chip, byt these are personal things.

To give you an idea what the arduino will need to do........

sample voltage X times per mS, output that figure over rs232, job done.

With the scope you need to set up and twiddle, The one thing I might need to do is code in some pre amble to tell total chrom its a GC, this is not hard.

Funny thing is arduino is now owned by microchip who make the pic. It used to be arduino was a toy, and pics were for the serious.

Its no longer true, arduino are now technically past the QDS and into stand alone modules. I hated arduino for a long time, but they have come a long way.

I Have used pics micros and sil labs ARM based ones for a long time, but if this was my project I would go with the duino. You dont need the power of sil labs, pics is too fudge for this, so i opted for simple.

QMR is a problem, but my thinking is the GC has some internal control to damp this, if not this is where home rolled code is needed, we simply slow the sample rate by doing 200 samples per 25mS then average them, out put the average.

That should filter down most noise, keep your expectations reasonable, the GC itself is highly limited. Also keep in mind, once that heating coil goes in oven, its likely game over.

Again I am a HP fan, any other GC is not worthy, so yeah I am biased.

SHADYCHASE54 - 12-2-2018 at 11:27

I finally found a operations manual for my GC I will try to upload the PDF in hopes that it will be of use to those willing to aid me with constructing a functioning ADC. I am still awaiting parts for the ADC and will make a post when I have everything I need.

[Edited on 12-2-2018 by SHADYCHASE54]

Attachment: 350 Manual[1].pdf (1.4MB)
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[Edited on 12-2-2018 by SHADYCHASE54]

NEMO-Chemistry - 13-2-2018 at 09:16

Ok that gives an idea what your dealing with, i didnt expect the current bridge. Makes things a bit easier in some respects. 10 bit resolution is all you need. The machine itself is effectively 10 bit. So going with a ADC higher than 10 bits wont give you more accuracy, it may at a push be needed, not for the accuracy but to extend the range.

Your dealing with a narrow range here, 1mV separations. It seems to have a 300mV range unless I have misread it, i will read again more carefully later. But just giving you a quick view from a read through.

My take at the moment is, the bridge while being run at 10 bits, is attenuated. Not that it matters much, but you are going to need a instrument grade rail to rail opamp.

Dont expect these to be super cheap, while not major expensive, to me they seem alot of money for what they are.

But keep in mind this was designed for a pen chart, the detection hardware (opamp bit) would of been inside that. All the charts recorders I have taken apart (4 only), didnt actually have great opamps in. Also what confuses me a little is the bridge regulation is by zener diode, in todays world a zener is not exactly cutting edge voltage regulation.

TBH a zener is the quick n dirty goto these days. So this makes me a bit skeptical of the bridge specs, hence on the reasons even a crap scope on a usb might be worth getting to look at the output.

While I read up on this manual, make sure you dont know anyone with a real oscilloscope, not a crappy usb one, but a real one. If you do happen to know someone, 10 mins on that sucker will give you all the info needed to build the output stage bridge.

The actual circuit and electronics, on this is experienced hobby level to sort out. The hard bit is knowing what you got to build around.

We what we know so far

1) 10 bit is plenty

2) its run in 1mV resolution

3) its a current bridge

4) 300mV max adjustment

5) with the above I would expect 0-1V levels tops

6)......You will need an opamp

I will come back and explain the opamp later, as we are now 100% sure its a current bridge, so your going to read the voltage drop off a resistor.

You could do it with a higher bit ADC but it will cost more to build the power source that it would to do it this way. Trying to measure uV is fine if you got zero ripple, in the real world even the bridge gives a ripple spec.

So rather than try and read uV, we boost the output with a opamp. I dont know yet how much, but likely 10X or 100X. This is actually controled by two simple resistors connected to the opamp.

For clarity, we are talking 1% resistors. i would go smd as they tend to be more stable and accurate in my experience. The bigger size smd resistors are not hard to solder with practice.

Go hunt down a chap with a scope, and I will read the manual again. Actually I am going to hunt down the service manual for a suitable pen recorder

. That will tell me what kind of front end they use on it. Then kind of copy the front end bit with modern bits.

But the good good news is..........1000% you can run that with matlab and serial data into a usb cabel, you can use GC software to calculate and draw the the output, but obviously we are not talking adjusting the machine via software!!!

NEMO-Chemistry - 13-2-2018 at 20:59

The USB scope is out, its 5mV resolution. Still cant find a schematic for a decent pen chart!! Dont expect great accuracy with this thing, the built in errors are fairly large compared to what the software normally works with.

I am more leaning with a simple approach and something like matlab or maybe simple graphs in C#. Doing alot of calcs on area isnt going to give much info. The accuracy just isnt there, if you go up to 12 bit bit ADC you will simply pic up the noise.

I might have the front of a pen chart in my spares box, I will try and find out what was used as the front end pick up. The more I read the less expensive i would be inclined to make it. Sure we could capture everything coming out, but you wont get a peak, or likely to get a mass of needle like spikes doing that.

Damping it down might actually give you better results. If your mapping the contours of a mountain, dosnt help you much if you measure Everest every mm. Some times better to work in feet than inches.

SHADYCHASE54 - 14-2-2018 at 20:31

I just wondered if this might have what your looking for.

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NEMO-Chemistry - 16-2-2018 at 03:06

Quote: Originally posted by SHADYCHASE54

I just wondered if this might have what your looking for.

If its got a schematic in it then yes its exactly what I am after. The file you gave just shows me the front page.

See if you can get a decent sized png of the schematic, if its got more than, then you after the one that shows from the input. We just want to know how they deal with the input and shape it.

Once we know that you can decide what you want to do. I would suggest you use Nitrogen, loads of reasons but mainly, helium to me shouldnt go into party balloons, and shouldnt be used when you have a reasonable alternative.

Its likely in the final design, you will have a load of blank spaces on the board. I suggest you spend the $20 and get the board made in china.

I will leave a section in the design but i suggest you dont actually populate it with parts unless you have too. What I am thinking is.....

It costs nothing to design in a damping system, with no oscilloscope to hand, and no way of me knowing what signal you get. Prudence makes me want to design in a damping system.

My gut says you wont need it, but if you do then you can add the caps and resistors and solder in a link wire. Then on the arduino/pic side of things, I will add in the software that looks for the link.

In a nutshell in psuedo code it goes a bit like this...

Is pin X high or low
if pin high then sample Y times in W ms and divide by Z

If pin X Low then just read and output

So software wise and hardware wise its no big deal to cover your arse, will save you doing it all twice.

These jobs are so much harder to do without the bloody machine in front of you. I am sure I could have done this over a weekend had you lived near me!

Probably for about £10

NEMO-Chemistry - 16-2-2018 at 15:14

Ok worked out the file!!! Didnt twig i needed to save as pdf sorry.

First glance.... isnt organized nicely to go straight to the information. They seem to of been coy about some the modules. But dosnt matter, is really old tech so most of it you wont need.

Surprised how much they jack the voltage up!! 400V! No idea why this is done, but then again i have no intention of looking up the datasheets for most the components.

I need some time to work out how they designed it, I know roughly what they done, but I need to check what the front end expects from the GC.

From the quick glance.....

GC passes current to the front mods, these simply use a resistor to give a voltage drop. One reason they might be using insane voltage is too do away with complex amplification, no idea how old this is, but probably circa 7014 opamps.

That would mean nastiness, alot of it. So we might not have to much signal conditioning at all, simply drop the current over a high precision resistor (ok not that high...1%).

I would still use a reasonable rail to rail instrument opamp to boost the signal. From that point on its almost single chip and software.

Going by gut feeling, I would take a couple long routes. Normally with a pic I tend to use the internal OSC, With this for what they cost I would go crystal OSC. That gives you a pretty accurate time base.

Next I would normally the internal voltage ref on the chip, if you use a good psu this is spot on. But in this case for a couple £, i would use a precision voltage ref for the ADC on the chip to read against.

The rest consist's of stuff you find in just about every micro circuit. ISCP setup for programing, max 232 for serial data, although with the usb cables these days you can use the serial output from the chip directly. But i still use the max chip.

Not much more to it..........

So recap

Turn the current to a voltage so the ADC can read it, this is done via a resistor. Ohms law connects resistance, current and Voltage. So if you got a Voltage you drop that over a known resistance and read the Voltage. This is directly proportional to the current.

In our case its a similar thing. The micro wont read uV directly, so you boost this with a opamp. every uV will be boosted to 1mV or maybe 100mV per uV (depends what the max output is). If the range is small enough then you will get high resolution with 10 bit. 1024 steps to be precise.

The rest is simple software, read the ADC 64 times in ~10ms average it, take that number and divide by 1024. This gives you the mV, output that over the serial line, plot it on a graph or other software.... Job done

wg48 - 17-2-2018 at 16:05

from the GC manual:

The output from the GC appears to be the raw bridge signal which is a voltage with a source impedance of between 32 and 64ohms depending on source impedance of the current drive to the bridge.

It recommends a chart recorder with a span of 1mV for maximum sensitivity and 1s response. and max chart rate of 2in/min.

The GC has a noise floor of 10uV rms max and a drift of 40uV/hour max.

If you assume the max sensitivity is achieved with the attenuator set at zero then you can decreases the signal amplitude but not increase it.

So how many uV should a bit/step represent and what should maximum voltage be ?.

Well ideally a bit should be no bigger than the noise floor and it could be smaller with filtering. Lets say no more than 10uV/ bit with at least a maximum range voltage of 1mv.. So an 8bit ADC with 3.9uv/bit would provide 1mV max. There is little point in increasing the resolution (reducing the uv/bit) unless the filtering reduces the noise and then you still have the drift. Its probably more useful to increase the dynamic range so you don’t have to repeat a measurement with the attenuator set lower to see the large peaks. So a 10bit DAC would be set 4mV range. For nitrogen or argon you might want +/- 2mV. to decode the positive and negative peaks. Idealy the DAC voltage reference would be referenced to bridge voltage reference but that would requre a new connection.

A HX711 is a single two channel bridge amplifier and 24 bit DAC with gains of +/-20mV or +/-40 and +/-80mV with 10sps or 80 sps . You can get one ready to go on small board for 99p from Ebay. Note it has only has 18 noiseless bits. It also has built in power line frequecy filters for 50 and 60Hz. Its intended use is for a bridge strain gauge type of electronic scales. It would provide a large dynamic range.

NEMO-Chemistry - 17-2-2018 at 17:09

WHAT??? I would edit but its been up a while, ignore the bits between the lines. I see your on about the amp side instead of the opamp use the DAC into the micro.

I edited the post but seems the first bit was missed.

----------------------------------------------------------------------------IGNORE HERE
How does it help? How are you then going to get the display on the pc? EVEN with that chip you have to connect a micro or something and then spit out raw USB or better still serial at the rate the GC works.

A opamp and 10bit is doing the same job as that chip except it can also get the data displayed.

I cant see the advantage, the reason for using a opamp is because its exactly how the detector in the pen chart works. Boost the signal and filter, mains noise is a simple 100nf ceramic cap across the rails. What you need to filter is the high frequency noise.

This is why i said a band pass and boost the signal so you just need to filter mains hum.

But if you can get that chip to display the signal.....

TO HERE
-----------------------------------------------------------------------------
You could connect that to a arduino, but 24 bit is overkill. I except it would give you a massive range, but I think thats asking for trouble.

I cant answer this yet, Some the GC manual is contradictory, it talks about the bridge in terms of 1024 steps, this would be 10 bit were it digital.

On 1mV range I think the penchart is 8 bit!! But dont quote that I havnt had chance to go through the schematics.

Mains hum is easy to take care of, a 10uF electrolytic cap and a 100nf ceramic cap job done. But these days its the high frequency stuff thats an issue.

Dont add any more ideas! Thats another data sheet i got to read! 99p is a tempting price though. But is it buying cheap problems?

Couldnt use it with a PIC 18f but it would leave us the arduino option. My gut feeling is its cheap but too sensitive. Worth reading the sheet though.

[Edited on 18-2-2018 by NEMO-Chemistry]

wg48 - 19-2-2018 at 01:19

Nemo: Why do you care that bridge amp and DAC I suggested is too sensitive or has too many bits. It not like its too expensive. Does it have sufficient sensitivity, at least the number bits to represent the voltage range required with sufficiently low nose and sufficient accuracy is what you need consider. Actually the accuracy is poor but it’s a ready to go solution for 99p. Any extra bits are bonus but they don’t have to be used but why not.

The number steps on the bridge current attenuator has very little to do with number of bits required on the DAC if your only digitising the voltage range of a paper chart recorder.

I am guessing but I would expect a modern GC to digitise most of not all of the dynamic range of the bridge sensor (about 18 bits) and store the result. Then only one run would required.

It probably better to pay more attention to your frontal lobes than your elementary canal or limbic system LOL and if you don’t want to read my suggestions don’t.

NEMO-Chemistry - 19-2-2018 at 03:52

LOL, I left the the bit I originally edited up, mainly because it had been up several hours before I spotted it.

Going to your question on bits, why do I care about it being 24 bits. I care because the guy isnt going to be able to trouble shoot much, 24 bits is above what is needed. Surely you can see the problems associated with this

It isnt going to help him with two opposites working on one problem, you go ahead and help him i will stay out of it.

I would take some time and think it through first, you have made some fundamental errors and assumptions, but cary on. I am interested to see how you get this onto a pc and filtered out to a signal you can use.

It would have helped alot more had you got its function right. It isnt a DAC!! Its the complete opposite to a DAC, looking at the data sheet its a ADC.

They are complete opposites, but i guess you think this dosnt matter either?

I dont care if you call an arm a leg, but if your going to operate on someone, its probably better not to tell them its a leg amputation and then cut the arm off.

[Edited on 19-2-2018 by NEMO-Chemistry]

wg48 - 19-2-2018 at 10:09

Wow I found a HX711 for 79 cents:
https://www.ebay.com/itm/1pc-Weighing-Pressure-Sensor-AD-Mod...

Perhaps a better chip is coming and they are trying to clear the old stock out.

NEMO-Chemistry - 19-2-2018 at 14:19

I look forward to seeing what you come up with.
The code side dosnt look too bad.

wg48 - 20-2-2018 at 05:21

Wow^2 here is an other bridge amp and ADC the CJMCU-1232 (ADS1232) 24bit about £3.50 from ebay but its higher accuracy to 0.1%, about 20 usable bits and down to 17nV rms noise Its probably a knock off of the Texas Instruments ADS1232 that has an even better spec.

https://www.ebay.co.uk/itm/CJMCU-1232-ADS1232-24Bit-Low-Nois...

NEMO-Chemistry - 20-2-2018 at 07:10

LOL off you go then, should take you 5 mins to knock up a circuit and connect that to a micro

.

You might want to read the pen recorder manual first, and re read the GC one..... just in case

I take it your assuming two things
1 it outputs a voltage

2 the voltage output is <100mV?

Looking at your other post i can see why you think this, i can also see why you might think from the manual. But i suggest before you go jumping on this and designing something, check the pen manual and read the specs again.

Out of interest what is your take on what is output on the back of the GC? I think you focused on the 1mV range without looking at the pen manual.

[Edited on 20-2-2018 by NEMO-Chemistry]

[Edited on 20-2-2018 by NEMO-Chemistry]

wg48 - 22-2-2018 at 06:55

Quote: Originally posted by NEMO-Chemistry

LOL off you go then, should take you 5 mins to knock up a circuit and connect that to a micro

Though my brain may be half dead the GC manual is far from rocket science so I am confident I can read it and comprehend it. I have no small experience in this area. Since you asked I will try again to explain it.

The manual unambiguously states at least a sensitivity of 1mV span (0 to 1mV) is required for maximum sensitivity of the GC. That’s a different ional voltage between the + and – terminals. Which I have already stated in one of my posts and apparently you already know??? (rhetorical question marks suggesting complexion). For signals larger than that, the bridge current attenuator can be used to reduce the signal to fit in the that 0 to 1mV span though a much better option is to use more bits and digitise the larger signals with the same resolution required of the 0 to 1mV span.

The manual does not give the largest differential signal on the output terminals as its not relevant due to the attenuator. However it is possible to guestimate the largest signal from knowledge of how the resistance of tungsten changes with temperature and the temperatures given in the manual. I guestimate it would be no more than 10% which would produce a change in voltage of approximately half that. Given the maximum bridge current of 100mA half of which flows through each 32ohm sensor filament (attenuator set to zero) the nominal voltage is 1.6V and 5% of that is 80mV. That’s perfect for the example of a low cost bridge amp and ADC I gave you. That would allow digitisation of the 0 to 1mV span and up to the full output of the bridge with a reasonable resolution.

Note: there may also be a common mode voltage on the + and – terminal of up to 1.6V wrt the third terminal earth/ground. I should also add the number of bits is an open question. I gave you a common strategy based in the noise floor of the bridge. There may also be practical, cost and processing considerations too. Usually more is considered better if other constraints allow. Testing them is insignificant as they are output in one serial stream.

The manual for any randomly selected paper chart recorder can not possibly tell you anything about the output of the GC any more than reading the manual of an oscilloscope or your fridge manual would. (just proof reading this now I think I know where your 600V comment came from the max voltage on chart recorder input voltage range selctor. The chart recorder is usually a general instrument like a scope its has nothing to do with the GC output)

My purpose in posting my comments was to help you in determining what was required in digitising the output from the GC. As, putting it plainly, from your comments you appeared be confused about it. Considerer my comments if you want or ignore them but throwing a tantrum and try to goad me are unproductive and is likely to make myself and others just think your talking out of the wrong end of your alimentary canal LOL.

Here is a Rolls-Royce 24bit ADC the LTC2411IMS. About £12 from Ebay so its expensive but not unaffordably so. It has almost a true 24 bits in terms of accuracy linearity and noise. No bridge amp and only about 6sps so probably not suitable for a GC but it would make a nice 6 digit DVM if you like lots of digit on your meter.

Shoot I almost lost this post but paging back and a resend and its back. It does help if I remember to hit Post Reply LOL

[Edited on 22-2-2018 by wg48]

Delete the chart recorder manual its confusing you

[Edited on 22-2-2018 by wg48]

NEMO-Chemistry - 22-2-2018 at 17:15

No one is arguing with you, go ahead come up with a design for the guy. I was honest, i am looking forward to see how you solve this the way you out lined.

I dont have your experience this is true, equally I have stuck to the same concept from the start, i havnt swung from get a 5mV plug in oscilloscope or PC plugin DAC to what you suggest now. I am also genuinely concerned you insisted on calling it a DAC until i pointed out the difference, might not seem much, but its the difference between an acid and a base.

So forgive me if I doubt your ability to build this and program it, nothing you have said so far has given me confidence. But I am like that, i actually love to learn and if you prove me wrong then great, I can learn far more from that than if I am right about it.

One question you didnt answer and I havnt looked it up, what protocol you going to use with the chip? I am kind of going to follow along using a different way.

Seriously stop getting hung up on what i say, I am positive your wrong but hope your right. I wont say any more I will watch how you solve this, i am always up for new ways to do things.

So as I said...........Over to you

wg48 - 23-2-2018 at 01:49

Quote: Originally posted by NEMO-Chemistry

Seriously stop getting hung up on what i say,

Now that is good advice.

SHADYCHASE54 - 27-3-2018 at 06:29

I have finally received most of what I was waiting for. I have bought an additional ADC 12 bit 1015/1115 however I am now wondering if I need it for this project? Considering the arduino uno has a 10 bit ADC included in hardware I am wondering, if I could find out the likely maximum voltage output of the Gow Mac GC and assuming it is low enough 1-1.5V max. Then 10 bit 1024 res. From 0 -1500Mv should be precise enough for identification of eluted samples? Just wondering if I might be on the right path with this thinking? The thing is building the hardware is simple as cookbook chemistry in that I have a schematic, understanding the why will take longer, programming the parameters however is throwing me through the proverbial hoop. As much as I am excited to gain a real understanding of circuitry, I am impatient to discover the functionality of my new toy. I write this so you know the project isn't dead for me and I would still appreciate any help and suggestions.

Best regards.

[Edited on 27-3-2018 by SHADYCHASE54]

NEMO-Chemistry - 27-3-2018 at 14:48

Hmm looks like the ideas stopped at plug on crap.

Ok can you give me a list of what you actually have now, just to save me going through the thread and working out what you did and didnt get.

List the lot including breadboards. I am free on Sunday for a few hours, so will sit down then and go through what we got. I have the penchart in bits, mostly its driver stuff for the pen servos and a damping circuit. The opamp in the one i got is a ........741!! Which seriously is not what i expected, bit like expecting a BMW and finding a pushbike.

But does have some really neat buffered stuff to make up for the utter crap Opamp they used lol. I will try it on perf board, but mostly its going on the arduino by the looks of it. Any way you can get access to a scope if needed? Would be handy for checking stuff.

Otherwise i will pm you my email, just send me the text files when we get that far, those will be from the 232 output and be the raw data i can graph. Past that and maybe a little Matlab there isnt anything else i can do at a distance.

So be prepared to run alot of known samples of things and see how far out the graphs are, without a scope its hit and miss whatever you use. But its a 10bit machine despite all the blah blah blah, not super accurate but pointless measureing to god knows how many decimal points when the actual output is fairly narrow.