Hi Bernard. I built the circuit using 300 ohms at R6 and 10k at R3,R4.The motor runs but there are some problems I can't seem to figure out. At powerup the motor runs but the photo transistor seems to have no effect. I played with R1 (the variable resistor) but nothing would get the motor to stop. Shorting across the transistor leads stops the motor. After doing that, pressing SW1 starts the motor up again but pressing it a second time does not stop it. Any thoughts?