555 PWM Servo Control

Use two 555's or one 556 and a 9V to accurately control a servo with a potentiometer. Cheap and easy, the pot. can be traded for a photoresistor as well. Note: Standard servos run on a pulse 1-2ms wide. 1ms is full reverse, 1.5ms is stop, and 2ms is full forward. The first 555 establishes a 1ms carrier signal on low. Although R1 has been set to 50k for easy analysis, in practice it should be about 400k to establish proper spacing between signals. Too fast or slow could cause jitter or power loss. The second 555 is triggered by the first. Output has a minimum 1ms duration of the trigger. A 22k resistor in parallel with a 100k pot. will ensure that the default pulse is 1.5ms when the wiper is centered, as well as cap maximum duration to 2ms(ish). Larger servos will need independent power. A more stable control can be achieved by running signal through standard motor control board (as used in remote control applications). Good luck, have fun!

published 7 years ago