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[on:]

I know it's not too likely, but I was wondering if there was a way to fairly accurately measure between about 100-1250 microamps without any specialized hardware. I'm interested in automatically measuring the gain of germanium transistors in two different situations automatically as shown at the bottom of this page (#26).

Thanks

[Reply #1 on:]

Last I tried something like this it was to measure a few TOhm.

I used one or two op-amps from TI... I believe it was OPA128 or something like that. The price for each of those was around 20 euro for small quantities and the care that was needed in the board design was a real nightmare. The project worked somewhat, but the scale involved (down to a few kOhm) and the non-linearity made it too problematic to consider bringing it to market.

[Reply #2 on:]

Hi,

Take a look at http://www.keithley.com/knowledgecenter  and get a couple of their handbooks.

In Semiconductor test, we used their "Electrometer" and other instruments. Measuring Picoamps requires shielding/guarding and excellent insulators.

[Reply #3 on:]

Simple resistor will do great job as current/voltage transformer, analogRead would digitize results for you.
For 100 microAmpers * 1 kOhm = 0.1V ( to stay away from noise floor),
and 1250 * 1 kOhm = 1.25 V accordingly.

[Reply #4 on:]

Would a linear analog Hall sensor be able to pick up on the moving charge field?

[Reply #5 on:]

Would a linear analog Hall sensor be able to pick up on the moving charge field?

No way too small by many orders of magnitude.

[Reply #6 on:]

This should not be too difficult. A 1k ohm resistor at 1mA will only drop out 1V, which is about the resistance of an analog meter.

So you could do this with a 1k from ground to the Ge transistor emitter and an analog input pin, and the collector of the transistor to 9V.

If you want or need better resolution, you could put an Op Amp in there to multiply the voltage x4, so at 1250uA there'd be 5V into the Arduino.

[Reply #7 on:]

which is about the resistance of an analog meter.

What sort or rubbish meters have you been using? Most analogue meters I have used have had 100K input impedance.

By the way have you seen my transistor testing project:-
http://www.thebox.myzen.co.uk/Hardware/Transistor_Tester.html

[Reply #8 on:]

"What sort or rubbish meters have you been using? Most analogue meters I have used have had 100K input impedance."

What sort of rubbish -current- meters have you been using? In context, I was talking about the current meter in the circuit referred to in the first post. Most analog -current- meters I've used have had around 1k (not K) input impedance.

Nice little transistor tester.