In the schematic shown on the Whiteboard during the episode, Ben shows the N-Channel MOSFET connected as a high-side switch without a high-side FET driver. Since the AVR and the motor are both referenced to the same ground, the motor will not receive the full supply voltage and the FET will operate in the triode mode causing excessive dissipation. Better would be to move the N-Channel MOSFET to the low side of the motor (connect source to ground and drain to "-" lead of motor). This way the MOSFET can be switched into the saturation mode causing much less dissipation and providing nearly full voltage to the motor. Another option would be to use a high-side FET driver between the AVR and MOSFET. The last option would be to use a P-Channel FET instead.
Granted in the specfic use case of the plant rotater, the MOSFET/motor are not on long enough for dissipation to become an issue. I just wanted to point it out to others/newbies that may try and adapt the circuit for other uses.
Shawn
