Here is a new firmware with B0 = output (Hi = PID Started, Lo = Pid Stopped). Please check it with a led, I just compiled it from my work, and din not tested it... (you also have all the binary files)
Please also note that PB1 is used already as input by the bootloader...!!!
Mihai
PS. I've also noted that you designed the board to use A4 as input for the thermal sensor. I will add code to check voltage value of A4 with ADC. Please tell me at what voltage I should stop the power stage. (I guess it depends greatly on the OP amplifier used)