I'm planning using Arduino as a switch to control electrical stimulation. I was told that a transistor would do the job, so I tried it, but the transistor can only stop electrical current of one polarity (I am using biphasic electrical stimulation in neuroscience research, and a transistor can only block electrical current of the positive stimulation during biphasic stimulation when it's "off". I want Arduino to act as something that can stop both positive and negative currents when it's off, and letting both pass when it's on.) We tried using two transistor (one NPN and one PNP) in a series circuit but still no luck.
Any suggestion will be highly appreciated.