This project was taken out of a popular science magazine. I have not been able to make it yet, so I don't have the arduino code. It costs about $50 and takes about 5 hours.

Step 1: Get Materials

You will need: 150-watt lightbulb and socket, Computer fan, Arduino Uno, Thermistor, Water, Mineral oil, 2 5-volt relays, 110-volt AC power source, Vial of DNA and reagents, 5 pieces of PVC: 4 to 3 inch adapter with 12 1/4 inch holes, 2 3 3/4 inch couplings, 2 4-inch wide pipes, Vial.

Step 2: Pile Up

TOP: Drill 12 1/4 inch holes into the top of the slanted adapter, fit a pipe inside the adapter's base, and cut a hole in the exposed pipe to match the computer fan's exhaust port. MIDDLE: Cut the same hole for the fan in the top of a straight PVC coupling and hot-glue the fan in place. Drill a hole into the coupling's side, just above the center, and bolt on a clamped lightbulb socket. BOTTOM: Drill a hole in a second coupling for a bunch of wires leading to the Arduino.

Step 3: Wire Up

Connect the socket and computer fan to 5-volt relays, and link them to the Arduino. Lead one socket wire to a 110-volt AC power source, and wire a thermistor to the Arduino. Insert the thermistor into a vial containing mineral oil and water, and put it in one of the 1/4 inch vial holes.