The microwave I used as a kid in the '80's did this. Dead simple, just a rocker switch riding on the motor shaft, triggered by the split pin that attached the t

The microwave I used as a kid in the '80's did this. Dead simple, just a rocker switch riding on the motor shaft, triggered by the split pin that attached the turntable base, which controlled power to the motor in parallel with the microwave controller. When the time was up the table would continue turning until the switch tripped. Stopped in the same place, every time.