heat element for 31 C/88 F tempeh/yogurt maker?

hey, i'm going to be making an Arduino yogurt/tempeh incubator. i need a suggestion for a very low-power heating element that will allow me to maintain a temperature of 31 degrees C and 88 degrees F...

it's be awesome if if could be powered right off the Arduino...

thanks for any suggestions. nym

I don't recommend trying to power something that generates heat "right from the arduino". You're going to want to use an unregulated supply to create the heat -- maybe a 12V transformer, switching the 12VAC with a triac and a 25w wire-wound resistor as a heating element.

"right off the arduino" you're going to be working with regulated 5V and every watt of heat you generate from the 5V is going to send a watt of heat out the voltage regulator. The digital outputs as-is can source or sink only about 50ma anyhow.

gardner: good to know that i'll likely have to power the heating element with something other than the arduino.

Richard - this is not an existing appliance...that is, there are commercial versions available but i want to build my own using a small cooler and an arduino, temperature sensor, and heating element/bulb.

31 C is quite a low temperature as far as heating element applications go. the cooler is well insulated, and after several hours of fermentation, tempeh begins to generate a little heat of its own. however, yogurt requires a little higher of a temperature - 43 C.

i will try to find out in advance how much power i will need.