Simple Servo Controller

Servo motors have many uses in everything from robotics to puppetry to photography and beyond. These little motors can position their output shaft to any position on command and hold that position. Most servos have a range of motion to about 210 degrees and thankfully are very easy to control with a simple circuit such as the one presented here. Using just a 555 timer and a few support components this circuit can control a servo through it's full rotation based on the position of a pot. This circuit was originally published in the Think Tankcolumn of the October 1995 issue of Popular Electronics.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 820 Ohm 1/4W Resistor R2 1 68K 1/4W Resistor R3 1 10K 1/4W Resistor R4 1 1K 1/4W Resistor R5 1 1K Linear Taper Pot C1 1 1uF 16V Electrolytic Capacitor Q1 1 2N3904 NPN Transistor 2N2222, Most Small Signal Transistors U1 1 555 Timer IC MISC 1 Board, Wire, Knob For R1, 8 Pin Socket For U1

Notes

1. R1 adjusts the position of the servo.
2. Connect the servo to the circuit as shown in the schematic. For common Futaba servos, the red wire is power, the black wire is ground, and the white wire is control.