PrototypingSeptember 21, 2004
The refrigerator consists of 3 main parts: The power supply, the motherboard, and the cooling chamber. The power supply is just a plain-old off-the-shelf PC power supply, which is beefy enough to supply the 8 amps of current needed by the peltier device.
The motherboard has a PIC16C771 microcontroller at its heart, which monitors temperature sensors on the heatsink and cooling chamber, manages the LCD display, watches the controls, turns the fan on when necessary, and adjusts power to the peltier device to try to maintain the target temperature. All the main circuitry for the fridge resides on this board.
The cooling chamber is made out of 1/4" and 1/8" aluminum plate. It has a 40mm peltier device, a heat sink, and a fan attached to the back. It is the job of the peltier device to pump heat out of the cooling chamber and dissipate it through the heat sink. I machined a solid aluminum spacer block for the back which provides room for an inch of insulation between the rear of the cooling chamber and the bottom of the heat sink. The cold-side temperature sensor (an LM335, covered by heat-shrink tubing) lives in a small hole drilled in the side of the spacer block.