The PCBs (to test the not yet written software using the Teensy3.2) have arrived and they test OK (except the one that I soldered the LM317 in backward!). I used an L293 Dual H-bridge driver for the fan and peltier device control. This way I can make the device shuttle electrons either way to warm or cool the heat-sink . The same goes for the fan, though I am not certain it will be necessary to drive the fan in both directions. The fan might end up being controlled by something else and I may use the second channel to drive a peristaltic pump, but again I don't know that I will need to drive that in different directions.