Presto Dehydrator Control Kit

Updated code: https://github.com/truglodite/Dehydrator

I decided to hack my Presto 6302 food dehydrator to control it with an Arduino 328p. The result is a smart dehydrator that uses a table of drying profiles (temperature and time) based on suggestions at printdry.com. The heater and fan are separately relay controlled, so the fan can run a little longer in holding mode after the heater turns off to prevent overheating of the appliance. In dry mode the temperature is controlled to the recommended drying temperature +- a hysterisis value, for the time recommended for the selected filament, and the fan is always on. After drying time has elapsed, it enters a holding mode, where humidity is controlled by hysterisis within +-1%, and the fan turns off when not needed. During holding mode the controller also makes sure the temperature does not exceed the holding temperature for the selected filament. The code makes use of #defines so you can customize almost every aspect of operation (ma