Lessons I learned:
- Do not use transistors rated for 200mA to switch something that is very close to 200mA -- if you get one that is slightly at the lower end of the tolerances on the spec, it'll burn out.
- A multimeter is the most important tool you have. Measure connections with the resistance-meter, measure voltages during operation, etcetera. Invaluable information when debugging.
- Open drain outputs are really cool.
Tomorrow, I will post up some photos of the various designs I went through, to document some of my stupidity for prosperity.