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?
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Mildronate
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yes you need data loger
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radagast
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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!
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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| 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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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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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!!
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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.
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That sounds pretty useful. How I would I go about building one?
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jwpa17
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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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