Stepper motor controller 555 timer circuits

This 555 timer circuits for circuit controls the speed of a stepper motor via the 100k pot, The direction of rotation is determined by the double pole double throw switch, stepper motor used in this circuit came from an old scanner. It had 5 wires: red-black-yellow-brown-orange,LED illuminate via the back-emf of the coils and prevent the spikes entering the transistors. The LED will flicker to show the pulses being received by the stepper motor, 27k stop-resistor limits the upper-frequency of the 555 and prevents the circuit producing pulses that are too fast for the stepper motor.