thanks, your idea really helped, but for muscle stimulation i need a way to change frequency in the 0-150 Hz range, the arduino pwm pins output a default 490 Hz and it is too much. Any functions to change that? or maybe some hardware tweaks to the circuit?
P.S.
i also need a way to change voltage and current, i could probably do that with resistors or potentiometers, but in muscle stimulation frequency is more important
P.P. S
here is the diagram of the circuit as it is now. as you can see i have 4 sets of electrodes (meant for 4 muscles) and they will be programmed to work in pairs (will probably use only 2 pwm pins instead of 4). Also i'm using mosfets instead of transistors
