I'm a first year electronics engineering student and I have volunteered to design and build a intracranial stimulator for a graduate psychology student's research project. The basic function of this device is to send a square wave pulse to a lab rat's brain. The current is small enough that the rat doesn't feel it. I'll be using the NI ELVIS II system, which already has a signal generator built in that is controlled by software. I would like to make the output around 5 volts DC so I can use digital circuitry for measurements and counters. I need to find a way to vary the current output of the device from 25uA to 250uA. Is there a way to vary the current without having to change the voltage? Any suggestions would be helpful...

 

You could try something similar to the attachment - requires an op-amp, power supply and other components. Basically a controlled current source. Not sure what resistance load it would "see" with animal tissue - presumably fairly low.

 

Ohms law applies even to rat skulls. If the varmint has constant resistance, one must increase the voltage to increase the current.

 

I use large quantities of black coffee for my intracranial stimulation.

 

I use large quantities of black coffee for my intracranial stimulation.

I find banging my head against the wall to work, also.

--Rich