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 Tank column 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
R1 adjusts the position of the servo.
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.
