The lab already had a picnic cooler, supposedly for climate-testing of the radiation detectors (?!). The cooler came equipped with a Peltier pump that can run off AC mains or 12V DC and can either heat or cool (depending on the switch setting) the box interior. Unfortunately, there is no thermostatic control built in, so the internal temperature either approaches approximately the ambient temperature less 20 degree Celsius or heats up to +50 Celsius and stays there (probably limited electronically).
This simply screams for some micro-controller driven decision making.
Aside from a picnic cooler, the final bill od materials consisted of:
- an arduino board
(we used a pro mini 328/5V/16M, simply because they are the cheapest Arduino clone on eBay @ $2.83),
- 2 relays (5V/1ch relay modules from eBay at $0.99 each),
- 2 momentary push-buttons (stolen from colleague Klemen)
[Klemen comments: "Borrowed not stolen. One day I will have them back."],
- an electronics thermometer (we used a DS18B20, eBay @ $1.04),
- 5 resistors (see schematics, later on),
- an LCD 2x16 display module (HD44780 compatible module, eBay @ $2.26),
- a 7805 voltage regulator (eBay @ $0.90) and its two decoupling capacitors,
- an electrical enclosure box from the hardware store ($6.00 for the cheapest one!),
- many, many, many... wires (depths of supervisor's drawer).