On Mon, 28 Jul 2008 20:52:07 -0400, Dave M
put finger to keyboard and composed:

A transimpedance amplifier is what you need, as Sam suggested. Here's a circuit
to start with. You might have to fiddle with exact resistor values, depending
on the Op-amp you use, which isn't critical, except for input offset voltage.
Select a dual Opamp with low offset voltage, such as the Texas Instruments
OPA2227.
Since it only sees DC currents and voltages, there are no issues with frequency
response. The circuit runs off a 9V battery ...

I don't mean to nitpick your clever circuit, but you've drawn it as
running off *two* 9V batteries. Maybe you should have designated the
battery terminals at V+ and V- rather than +/-9V.

+9V
|
+-+-+
| |
| | +-------------+
10K | | | |
1% | | | +9V |
+-+-+ | | |
| | |\ | |
| | | \| |
| +--+- \ |
| | \U1B |
| | ------+
| | / |
+-----------++ / |
| | /| |
| |/ | |
+-+-+ | +++
| | -9V +
| |
10K | |
1% | |
+-+-+
|
-9V


Cheers!!!
Dave M

Never take a laxative and a sleeping pill at the same time!!

Wise words.

- Franc Zabkar
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