While in theory the board almost worked, it mostly didn't. The first issue was I messed up the footprint on the single op-amp. Looking back at the datasheet there were three different pinouts for the SOT-23-5 version, none of which had a model that corresponded to the part I ordered. Outstanding.

The first rev of this board was meant to be a quick breadboard proof of concept. After I had wired up an additional analog output from the trinket to be my reference voltage since i screwed up the voltage divider buffer amp, I had outputs coming from the board in the appropriate range. However after some poor probing I burnt out the 5V breadboard supply that failed into an open state, passing the transformer input to the 5v rail. While this worked OK, and quickly brought the thermistor temperatures very high, since the voltage reference wasn't working, the Op amps saturated and I just got max readings from the trinkets analog inputs. So I had to settle with testing with the 3.3V rail off of the breadboard supply, as the trinkets onboard regulator would get pretty warm trying to run the sensor. The mosfet control seemed to be working to control the voltage applied to the divider, but the low voltage supply didn't seem to warm up the thermistors at all.

While I didn't have warm thermistors I tried to get some measurements anyway. Since the Trinket can program over the USB but not do serial over USB by default, I threw on this EBay Serial Bluetooth adapter, and loaded up a serial terminal on my phone. That worked OK for some quick and dirty output.

It looked OK until this point. This is when the real problem reared its head. While I could measure a solid voltage off the output pin on my board with the multimeter, the analog inputs on the trinket were all over the place. Easy +/- .25 volts. This seems pretty odd as I had filters on the output from my board. I'm sure there is something I'm missing, but the board needs to be respun and redesigned anyways. Maybe the board could use that onboard ADC. Plus a well designed board should either plug right onto the trinket board, or just stand on it's own. Also on the redesign agenda would be to use NTC thermistors instead. For whatever reason the PTC ones I choose have a pretty small range of resistance and cost a lot.

Anyways, today is the end of the contest entry period, so whatever I have at this point is my entry. Also to fulfill my obligation to the contest rules I'm currently uploading a video of myself rambling on about my project to and pointing at my breadboard for a few minutes. Riveting entertainment, I know, but its in the rules. I don't want to disqualify myself.

Hopefully my next update will have some better results.