In most good horror movies there is a mad scientist (or mad engineer?) who needs to turn on his equipment for bringing a monster to life or other such thing. Typically there are big sparks as the switch makes contact as it does not have suitable suppression circuitry.

3D model

I loved the idea of having such a switch but did not fancy having live electricity exposed to the users and real sparks are fun but also not that safe.

 

So I built my own knife switch. The first step was to model it in CAD, I used Fusion360 for that and experimented with different sizes and layouts. I also sourced some lovely brass screw terminals which I incorporated into the design. Most of the parts were made using metal, plastic and wood with a 3D printed cross bar.

Contacts

 

So the switch does actually work as a two pole single throw switch. The background was made from clear polycarbonate with a lightning bolt taped on, that was spray painted black and then the tape removed.

 

A buzzer and LED Backlight provide the light and sound for the arching which is trigged by a 3.3v Arduino NanoArduino Nano.

 

So that I could actually control something, I used a Pi-MotePi-Mote RF control board and Energinie switch. The Pi-Mote uses 6 pins to signal to the switches but these are just simple digital toggles so you don't need to use a Pi with it, other boards such as an Arduino work too and I found a great library from Jiri Dohnalek https://github.com/learn2develop/Arduino_Energenie_Pimote  that simplified my code.

The Pi-Mote is designed to work with a Raspberry Pi so ensure you use 3.3v logic levels.

 

https://github.com/Workshopshed/HackSpace/tree/master/KnifeSwitch

 

Knife Switch