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Hobby Servo Tester or Hobby Servo Controller

by Al Margolis, founder

This simple circuit uses a 555 timer chip to provide the control signal required by common hobby servos. I started this project to help a robot builder who was having a hard time deciding if he had a bad servo or a software bug. It has also been used for interactive displays and for various gadgets where a hobby servo is a cost effective way to provide movement proportional to the turning of a knob.

Breadboard Layout

Parts List

IC1LM555CN 1011 Add To Cart
Q1PN2222 1378 Add To Cart
R115K ohm (brown, green, orange) 1533 Add To Cart
R210K Potentiometer 1567 Add To Cart
R3220K ohm (red, red, yellow) 1304 Add To Cart
R410K ohm (brown, black, orange) 1432 Add To Cart
R510K ohm (brown, black, orange) 1432 Add To Cart
C1,C2.01uf ceramic capacitor 1033 Add To Cart

Additional Project Ideas

For direct control application, you will probably want to replace the trimmer potentiometer (R2) with a full size potentiometer (available from Radio Shack and other sources).

End of Project

This application note is a work in progress. If you found it interesting, awful or incomplete please let me know by sending email to

The content on this page was updated on 09/27/2004