I'm helping @Nathan Roberts with his tongue zapper project. Some aspects of what he needs are very similar to a project I did that used a constant-current H-bridge to drive 600µA into ear lobes with a wave profile including changing polarity. That was one channel.

The tongue stimulator project requires 16 channels, which the signal will rotate through. So several pulses on one channel, then the same pulse profile on the next channel, and so on. So the challenge is how to switch the H-bridge output (up to ~6mA constant current, either polarity) sequentially to 16 channels.

I was looking at a demux IC such as 74154 but it wouldn't really work. I could handle the BCD input but the output wouldn't really support changing polarity.

Any ideas? Brute force would be to use a current-control circuit for each output channel. That seems very inelegant.

 

You just need an analog multiplexer using dual supplies that can handle bipolar signals such as this.

 

"At any instant in time, one of the 16 electrodes in each of the 9 sectors on the array is delivering stimulation. The remaining electrodes serve as the current return path to ground."

this has me dumbfounded. so there is always 9 signals at any one time (i think 8 would be fine) going to 9 banks of 16 electrodes and the remaining 15 electrodes in each bank are grounded.....BUT does the next set of pulses then move to another electrode? essentialy one of the 15 grounds become the signal wire then the old signal wire changes to ground and the the cycle repeats. so every one of the 143 electrodes has a turn at being a signal electrode? or am i reading that wrong...

 

...or am i reading that wrong...

That's the way I interpret it.

Note that the IC linked by crutschow can handle only 5mA. So that may not be the exact IC to use if you need 6mA, but it shows that the kind of chip you need is probably out there. I haven't hunted for an alternative. To make it work, you'll also need a chip that can convert your clock signal to BCD, binary coded decimal, up to 16. Lot of ICs can do that, they're called counters.