How to make Arduino act as a simple switch?

Hi all,

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.

"Solid State Relay"

We tried using two transistor (one NPN and one PNP) in a series circuit but still no luck.

It's very unlikely that luck can compensate for missing knowledge it such a situation. For controlling currents in two directions usually a H-Bridge is used

What voltages and currents are involved? How quickly do you want to switch them? A relay might be a simple answer.

MarkT: What voltages and currents are involved? How quickly do you want to switch them? A relay might be a simple answer.

It's between 100-200 Hz,0.1-10 mA (0.1-10 V), 50-200 uS pulse width, biphasic stimulation.