Controlling current

I'm working on a project involving a number of circuits between 0 and 6, using a microcontroller to dictate which of the circuits will be open. I'm using a square wave AC current, and I'm trying to ensure that the current through each circuit is some value +-X (probably between 1 and 5 mA, I need to do some testing) regardless of the number of circuits open. The resistance is unknown and variable, so simply monitoring the voltage won't work. The maximum voltage is +-5 V.

What are some ideas for how I can do this?

I'm wondering if it might be possible to find an IC that can limit a current to A*X (where A is the number of circuits open) for DC, and put two of those in parallel in opposite directions with diodes in place to prevent backwards current flow.

Thanks for your help

You had better tell us what these circuits are and what you're actually trying to achieve because your current description illustrates you don't understand.

Your explanation of waning AC and using diodes to prevent reverse current is the obvious indication.

Don't be so secretive. Tells us what it is you're trying to switch and what you're trying to achieve.

They involve skin conduction and I *know* I'm going to get in trouble for that (indeed, basically got harangued off another forum for it just the other day), but I'm not building anything until I get the approval of a neurophysiologist and an electrical engineer.

It seems to me that sticking a parallel branch in the middle of the circuit with a diode on each in opposite directions should divert current to one or the other depending on the instantaneous sign of the voltage, which would allow DC circuitry to be used on the branches.