Tech Artificer

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TA-01 · June 2021

Knife Switch

A knife switch with a built-in speaker and haptic buzzer. Throwing it plays a sparking sound with a haptic pattern to match, and brings the rest of the room to life.

Materials
Poplar, copper, silk-wrapped wire
Electronics
Raspberry Pi 4, stereo amplifier, haptic motor controller, speaker, mini motor disc
Integrations
Home Assistant
Status
Complete (and used every day)
A wall-mounted knife switch: a poplar board with two copper blades joined by a wooden crossbar and a black handle, with silk-wrapped wires running from the contacts.
The finished switch

01Wood and copper

The switch is made of poplar and copper. The wires are silk-wrapped to give it an older feel.

The haptic buzzer on the blade is a Vibrating Mini Motor Disc (opens in a new tab).

A bent copper blade seated in a copper contact clip screwed to the poplar board, with a silk-wrapped wire attached.
Blade and contact
Close-up of a copper hinge contact at the bottom of the switch, with a twisted silk-wrapped wire.
Hinge contact
A small coin-shaped haptic buzzer mounted on the copper blade, its fine wires running into a silk-wrapped cable.
Haptic buzzer on the blade

02The brains

A Raspberry Pi 4 Model B (opens in a new tab) is at the center. It detects the connection, plays the audio, and triggers the haptics.

It also calls Home Assistant to turn on lights, monitors, and other devices, and plays the WarGames WOPR sound on other speakers in the room.

The electronics box holds an Adafruit Stereo Audio Amplifier (opens in a new tab) and an Adafruit Haptic Motor Controller (opens in a new tab).

An open black electronics box with connectors on its side, sitting on a workbench.
Electronics box
Inside the electronics box: small circuit boards and twisted pairs of colored wire.
Amplifier and haptic driver
The closed black electronics box mounted on a wall, with silk-wrapped cables plugged into its connectors.
Box mounted and wired
The knife switch on the wall with its silk-wrapped cables running down to the electronics box below.
Final installation