Combine an ECG headset with an Arduino to control paramecia!

Paramecia display a behaviour known as galvanotaxis: movement in response to an electrical field. If an electrical field is generated across the water they are swimming in, they will turn to orient themselves to the field and will swim towards the cathode (negative terminal).

The mind control mechanism takes advantage of this: I developed a laser cut stand with a small (14mm x 14mm) well in it to hold paramecia. By placing electrodes (pencil leads) on each of the four sides of the well and attaching them to four I/O pins on an Arduino, I can use the Arduino directly to send 5V at a few tens of mA through any pair of electrodes. This establishes a field of about 3.6 V/cm, which is right in the sweet spot of the field strength that paramecia respond to.

Build instructions here. [via Hacked Gadgets]