For larryd’s suggestion, a current comparator circuit seems straightforward enough and should give me the ability to switch from +120mA to -120mA. I’ve looked around at some constant current circuits too. It seems like I should be able to feed a constant +/-120mA to the current comparator and have it do the switching. I would also need a switch to turn off the current for that bit of time between the 1ms pulses. So basically three different parts all controlled by the arduino.
For DrDiettrich, I have an electrical muscle stimulation (EMS, very similar to a TENS unit) machine which is partly what sparked my interest. It uses a constant voltage waveform. I could set it to produce a constant signal and then check the voltage, current and even the waveform using my multimeter and oscilloscope.
Grumpy_Mike, from what I looked at I can use a constant current circuit before the current comparator. The constant current circuit can be set to hold at 120mA listening to feedback and then the comparator will do the actual pulsing. Does that sound plausible?
MorganS, I took a stroll through the wikipedia and I understand the basic concept but I think you’re right about it being too complicated without having an engineer to tweak it. Also most of the applications were for voltage, like in a computer PSU so I’m not sure which commercial applications I could potentially scavenge from if I did decide to go that direction.
I found a neat open source project called pulse pal that can generate a variety of waveforms using an arduino due. The waveforms control voltage so while the hardware may not be too relevant I think the open source code would be. I also stumbled across this in the switch mode power supply wiki: “When equipment is human-accessible, voltage and power limits of <=42.4 V peak/60 V DV and 250 VA apply for safety certification.” So now we have a voltage limit for safety