Mini Green House
I need to plant tomatoes soon and I've had issues with this in the past. This year I want to build a small Arduino based temperature controller.
Logic is pretty simple. Take a measurement, if the temp is too low, turn on the heater and fan. The heater runs for 3 seconds, the fan for 5.
The heater will just be a mass of resistors. They shouldn't need to put out a lot of heat to be effective.
I already have the light for this. I'll arrange a wall around this made of insulation - I think I have enough scrap. If not, cardboard should provide decent insulation.