PWM

The circuit is a basic servo motor controller/positioner based on the 555 timer operating as a variable duty cycle, constant frequency astable multivibrator (see the circuit 555 Variable Duty Cycle, Constant Frequency Astable Multivibrator). From the generalized circuit the values of the components were tailored for this specific application. Potentiometer Rdcadj adjust the duty cycle with slight effect on frequency. This is for servo motors with the following specifications: Power Supply = 5 V nominal Control Pulse Repetition Rate = 50 Hz (20 ms / cycle) Counterclockwise/Left/0°(-90°) Control Pulse Width = 1 ms Neutral/Midrange/90°(0°) = Control Pulse Width = 1.5 ms Clockwise/Right/180°(+90°) Control Pulse Width = 2 ms This is the basic circuit, additional components can be added to optimize the performance of the circuit.