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Cheesasaurus
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[*] posted on 24-5-2013 at 06:00
Constructing digital chart recorder?


Hi there,

My lab has a really old school chart recorder hooked up to a UV spectrophotometer for measuring absorbance of mRNA/protein samples. It works fine (bar some fiddly bits at the start of a run when setting it up) but I was wondering how easy it would be to cobble together an analogue to digital converter and output the spec readings to a computer instead?

To integrate the curves produced at the moment we get an A3 enlargement, cut them out, scrunch them up and weigh them on a fairly sensitive balance (going by the assumption that a bit of paper is the same thickness all the way along) but I think it would be really handy to be able to get a more accurate (and less time-consuming!) way of doing so.

So yeah, my question is: Digital chart recorder - a) would it be fairly simple (and cheapish) to put together and b) would it be able to work in the setup I've described?
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Mildronate
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[*] posted on 24-5-2013 at 07:05


yes you need data loger
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radagast
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[*] posted on 24-5-2013 at 07:15


Quote: Originally posted by Cheesasaurus  
Hi there,

My lab has a really old school chart recorder hooked up to a UV spectrophotometer for measuring absorbance of mRNA/protein samples. It works fine (bar some fiddly bits at the start of a run when setting it up) but I was wondering how easy it would be to cobble together an analogue to digital converter and output the spec readings to a computer instead?

To integrate the curves produced at the moment we get an A3 enlargement, cut them out, scrunch them up and weigh them on a fairly sensitive balance (going by the assumption that a bit of paper is the same thickness all the way along) but I think it would be really handy to be able to get a more accurate (and less time-consuming!) way of doing so.

So yeah, my question is: Digital chart recorder - a) would it be fairly simple (and cheapish) to put together and b) would it be able to work in the setup I've described?


The 1980s are calling and want their weight-based integration methods back!

Check out the following thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=22893#...

In a nutshell, UBS A-to-D converters are quite inexpensive (I used a ~$30 DATAQ 145 for my Perkin-Elmers Lambda 3B, and the DATAQ device came with primitive data-capture software).
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Cheesasaurus
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[*] posted on 27-5-2013 at 07:53


Quote: Originally posted by radagast  
Quote: Originally posted by Cheesasaurus  
Hi there,

My lab has a really old school chart recorder hooked up to a UV spectrophotometer for measuring absorbance of mRNA/protein samples. It works fine (bar some fiddly bits at the start of a run when setting it up) but I was wondering how easy it would be to cobble together an analogue to digital converter and output the spec readings to a computer instead?

To integrate the curves produced at the moment we get an A3 enlargement, cut them out, scrunch them up and weigh them on a fairly sensitive balance (going by the assumption that a bit of paper is the same thickness all the way along) but I think it would be really handy to be able to get a more accurate (and less time-consuming!) way of doing so.

So yeah, my question is: Digital chart recorder - a) would it be fairly simple (and cheapish) to put together and b) would it be able to work in the setup I've described?


The 1980s are calling and want their weight-based integration methods back!

Check out the following thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=22893#...

In a nutshell, UBS A-to-D converters are quite inexpensive (I used a ~$30 DATAQ 145 for my Perkin-Elmers Lambda 3B, and the DATAQ device came with primitive data-capture software).


That's awesome, thanks! I'm dealing with fairly small inputs (potentially in the region of 10mV) and the model you've suggested has a resolution in the range of 19.5mV. Do you know of something still relatively cheap but with a slightly higher resolution?
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jwpa17
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[*] posted on 28-5-2013 at 16:14
Amplifying signal


I think you'd be better off to amplify the signal, rather than try for a higher resolution A/D.
Suppose you have a 10 bit A/D, with an input range of 0-10 volts. Ten bits is 2^10, or 1024 ~ 1000 possible numbers. So this A/D can resolve signal differences of about 1/1000 of 10 volts, or 10 mV. If you have a 10 mV signal, you can "see" 0's and 1's. But if you amplify that signal by, say, 100 x, then it will be ranging from 0 to 1 V, and you'll have better resolution.
You get the best performance, resolution-wise, if the signal matches the input range of the A/D.
It isn't terribly hard to build a 100X amplifier from op-amps. I've built 1000x amps as well, but usually had noise problems.
Good luck.
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neptunium
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[*] posted on 28-5-2013 at 17:22


i have been looking into radio astronomy for some times ...there is a software (free) at radiosky.com its called skypipe ll and it works with the sound card....cant make it easier and its free!!



Http://www.d-radlab.com/
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Cheesasaurus
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[*] posted on 29-5-2013 at 01:43


Quote: Originally posted by jwpa17  
I think you'd be better off to amplify the signal, rather than try for a higher resolution A/D.
Suppose you have a 10 bit A/D, with an input range of 0-10 volts. Ten bits is 2^10, or 1024 ~ 1000 possible numbers. So this A/D can resolve signal differences of about 1/1000 of 10 volts, or 10 mV. If you have a 10 mV signal, you can "see" 0's and 1's. But if you amplify that signal by, say, 100 x, then it will be ranging from 0 to 1 V, and you'll have better resolution.
You get the best performance, resolution-wise, if the signal matches the input range of the A/D.
It isn't terribly hard to build a 100X amplifier from op-amps. I've built 1000x amps as well, but usually had noise problems.
Good luck.


That sounds pretty useful. How I would I go about building one?
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jwpa17
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[*] posted on 29-5-2013 at 12:54
Not to be trite, but


Google is your friend.
I'm sorry, but I'm not really able to give you a crash course in electronics today. Here's a start: http://en.wikibooks.org/wiki/Electronics/Op-Amps You might look into this book "How to Build and Use Electronic Devices Without Frustration Panic Mountains of Money or an Engineer Degree," which is kind of a practically oriented, self-instruction guide to electronics.
It seems to me that you don't really need a highly accurate and precise circuit, only a stable one. That is, your teacher will likely want to compare results of one run to another, but not too often compare an experimental spectrum to a published one. Even in our lab, results differ slightly from one instrument to another.
Dataq.com sells "signal conditioning" circuits, but they're probably more expensive than your teacher wants to buy.
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