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Op Amp help requested

 
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DoctorLes
Semi Newbie


Joined: 30 Aug 2009
Posts: 5

PostPosted: Sun Sep 13, 2009 5:36 pm    Post subject: Op Amp help requested Reply with quote

Hi,

I have been working on a project for quite awhile now but keep running into detours and dead ends, so thanks in advance.

I've searched the Net and several books high and low but am still pretty much confused about what I need. Also, none of the "Practical" circuits I have come across give sufficient component data for me to build my own, or else they are not appropriate for my application.

Goal: I want to boost my infrared thermopile's voltage output from about 0.2 mv to high enough to drive an analog input for my Arduino microprocessor but I'm not sure how much that will need to be. The thermopile has an internal ambient temperature compensating resistor; the changing value needs to be sent to the Op Amp too.

The output of my Arduino then drives a serial port/USB converter cable/circuit. Then I convert that data to a dynamic graph to be read on my computer (I have Mac, Linux and Microsoft platforms available, but Mac seems easiest to use right now).

My Arduino is using a single 5V USB power supply, so I need to use this single voltage source for my Op Amp circuit. I don't want to fuss with an external twin battery supply but I will if I have to, I guess. So I figure the Op Amp circuit has to split the USB supply voltage, giving the max output voltage of just under 2.5 VDC, at full amplification.

So, for all this I think I also need a low noise Op Amp with a low minimum operating voltage range. I think I need to use an instrumentation amp design with some kind of buffering stage. Right now, I have an LM324N Quad Op Amp chip but can get others, of course.

Summing up, I would like advice on which type of Op Amp circuit to use, what type of chip characteristics should I look for (perhaps with a suggestion of one or two chips to try) and where I might be able to track down component values. I realize components determine the amplification and such, using formulas, but it's mostly the other components that leave me in doubt, such as bypass capacitors, etc.

Thanks Again,

Les
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friendlyzookeeper
HG Junior


Joined: 26 Apr 2009
Posts: 10
Location: USA

PostPosted: Mon Sep 21, 2009 10:40 pm    Post subject: Reply with quote

Hey,
I'm not into that circuit at this time, but I have read something really similar. It wasn't under op-amp, but under logic converter or level shifter ICs. I can't remember off hand. It was with an avr board and the circuit was written up in a data sheet. Sorry I couldn't be any help, but will keep an eye open for it. Its that I have thousands of data sheets.
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DoctorLes
Semi Newbie


Joined: 30 Aug 2009
Posts: 5

PostPosted: Tue Sep 22, 2009 9:22 am    Post subject: Reply with quote

Hey,

Thanks anyway.
Currently, I'm investigating "chopper circuits" which might fit my bill. But if you turn up something I'd be much obliged. Especially if component values are displayed.

Regards,

Les
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friendlyzookeeper
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Joined: 26 Apr 2009
Posts: 10
Location: USA

PostPosted: Tue Sep 22, 2009 3:43 pm    Post subject: Reply with quote

Hey,
Would you be talking about chopper amplifiers or chopper circuit? The chopper circuits that I remember was in my motor control class a long time ago. It was a circuit to break a contact to create a delay or power up a motor. This is old school and I would not recommend. Good luck and I will look for the op amp circuit. Hope I have any luck at it. So, far with none.
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