Tech Tip: Using a Servo Motor to Operate a Door Lock

In today’s technologically advanced society, the desire to remotely operate doors is becoming increasingly widespread. The good news is that you can use a simple circuit with a relatively inexpensive servo motor to perform this function. This project can be further expanded to operate wirelessly using a basic remote control.

A servo motor operates on a system based on sending three different pulse widths to the unit to produce movement that ranges from 0 to 90 to 180 degrees. A 1 ms pulse width will position the motor to the extreme left (0°), a 2 ms pulse width will position the motor to the extreme right (180°), and a 1.5 ms pulse width will position the motor in between these two extremes (90°).

This operation can be used to actuate a door lock or a latch to enable you to remotely lock and unlock a door or gate. The required circuit is a simple pulse generator based on a 555 timer, Arduino, or PIC microcontroller. Any of these circuits can be combined with the RF remote control modules listed on

The circuit described here will be implemented with a 555 timer IC, since it is easiest to assemble and does not require any programming knowledge. The scheme is to switch in three different value resistors to select the three different pulse width values required. The required values are determined from the timing equations for the 555 timer. Using a standard 0.1 uF capacitor, we would need values of 10K for 1 ms width and 24K for 2 ms width.

The circuit shown below can be implemented as a wireless remote control using any suitable RF module such as the RXD4140-434 module in place of the pushbutton switches.

Circuit Diagram
Click to enlarge



George Leger has a Masters in Electrical Engineering from Stanford University, worked in private industry pioneering surface-mount technology and in government research labs for twenty years, published several papers on surface-mount technology, co-authored papers published in national symposiums on accelerator technology, was past president of SMTA and an adjunct professor at the community college level, holds a patent, and is a certified microchip design partner, serving as a consultant to many companies developing electronic circuits.

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