Evening Electronics 101

In these informal meetings we learn the basics about new electronic components, and develop ideas how to incorporate them in fun and instructional hands-on projects. If you are interested in joining, please email one of the organizers.

Next event: Tuesday, Nov 9, 6pm, Small 230.

Objective: Each group develops a concept for the enclosure of the NE555 code lock. Complete the design and fabricate the enclosure until the next meeting on Nov 23.

Organizers: Jens Boos and Ran Yang.

Past events:

NE555 servo code lock

The idea of this project is to use the NE555 timer integrated circuit to control a servo motor. This way, turning a knob will make the servo mimic that motion. Building this circuit more times, we can control as many servos as we want, each one with their own knob.

Now to turn this into something fun, it's our goal to have each servo act as a locking mechanism inside of a box, so only when all servos are aligned the right way you can actually go ahead and open the box. So it's basically a mechanical code lock!


This simple circuit generates an output signal between .7ms to 4ms, depending on the position of the potentiometer. A typical servo needs 1ms to be in the zero degree configuration, and 2ms to be in the 180 degree configuration.

If you want to use your own values, the ON time can be calculated like this (in milliseconds):

t_ON = 0.69 × (R1 + R2) [kΩ] × C1 [ μF ] ms

Make sure you insert the resistor values in kΩ and the capacitor value in μF for this formula to work correctly.

Parts list

It is recommended to add the parts decorated with an asterisk for stability of the circuit, but they can be omitted for a first proof of principle.

NE555 pinout

Useful links