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Author: Subject: Constructing digital chart recorder?
Cheesasaurus
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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?
Mildronate
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yes you need data loger
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 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!

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). Cheesasaurus Harmless Posts: 3 Registered: 24-5-2013 Member Is Offline Mood: No Mood 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?
jwpa17
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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.
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.
neptunium
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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!!

Cheesasaurus
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 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?
jwpa17
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Not to be trite, but