/building · 2012

Touchscreen Light Switch

$45 surplus screen · linux · java

A forty-five dollar surplus touchscreen set into a plywood wall panel, running a Java applet that asks Jarvis to switch the room's lights over SSH.

A wall-mounted touchscreen showing a grid of labelled lighting buttons

A warehouse of surplus electronics had a touchscreen LCD and a matching driver board for forty-five dollars together. That price is the reason this project exists. At forty-five dollars you will happily cut a hole in a wall panel to find out whether it works.

The bare LCD panel wired to its driver board, showing an Ubuntu boot screen
The driver board and ribbon cable laid out on the back of a plywood panel
A rectangular cutout in a plywood panel with the screen dropped into it
The finished wall panel showing a grid of labelled lighting buttons
Booting the panel on the bench, mounting the driver board, cutting the enclosure, and the interface it ended up running.

The enclosure is plywood with a rectangular cutout, with the driver board mounted on the back and the whole thing set into the wall so only the glass shows. Behind it is a small Linux machine.

The interface is a Java applet: a grid of large buttons, each one an icon and a label for one thing in the room. Overhead, accents, ceiling, bookshelf, floor lamp, bed lamp, monitor, speakers, and a button that turns all of them off at once. Pressing one opens an SSH connection to the machine running Jarvis and asks it to throw the corresponding relay.

That indirection is the reason the panel was worth building. Jarvis already knew how to switch every circuit in the room, so the touchscreen didn't need to know anything about relays. It needed to know what the buttons were called and where to send them, which is a small enough program that a Java applet from 2012 could hold all of it.

cd /building