hobby Dec 2023 → 2024

A real traffic light, under our control

A genuine pedestrian traffic light arrived as a Christmas gift in late 2023, legitimately acquired, but with no driving electronics. The original controller had been on a separate pole that did not come with it. The project, then: get the thing to light up, then keep going.

Step 1: getting it open

I 3D-printed an opening tool, took the front off, and figured out the wiring. The original logic had lived elsewhere; the cables coming out of the pole were one per lamp, each switched by whether or not it saw 240V AC. So control meant switching three independent mains connections.

The pedestrian traffic light standing in the kitchen, unlit. Three stacked lamp housings on a concrete base. — As received. Three independent 240 V lamps, no controller, ready for retrofit.

Step 2: Raspberry Pi + relays

A Raspberry Pi Zero 2 sits inside the housing. The original casing has plenty of dead volume, so it fits cleanly out of sight.
Three mains-rated relays, one per lamp, switched from the Pi's GPIO.
Each lamp is either fully on or fully off. There is no PWM here, just clean AC switching.

Step 3: web UI

A small web app runs on the Pi, served on the local network at trafikklys.local via mDNS. From any phone in the house: pick a mode, run a sequence, trigger one-off effects.

iPhone screenshot of the trafikklys.local web UI: three rendered lamp circles, top red and bottom green active. — Web UI on `trafikklys.local`. Direct lamp control from any phone on the LAN.

The physical traffic light with the top red lamp and the bottom green lamp lit at the same time. — And the same state on the actual hardware: red and green simultaneously, which a real crossing would never do.

Step 4: Sonos-reactive party mode

Hooked into the room's Sonos system. The light blinks along with whatever the speakers are playing, and a separate "drinking games" mode runs scripted timed sequences: green when it is your turn to drink, red when it is not. The most used feature by a wide margin, beating both the original lamp function and the music-reactive mode.

The physical traffic light with two red lamps lit and the green lamp dark. A state that exists only because we can now do whatever we want with the three lamps. — Two reds at once. A state the original controller would never have produced.

What I learned

That hardware projects need a product brain, not just an engineering one. The feature I considered the headline (music-reactive) got shown to people once and never demanded again. The scripted party mode is what people actually use. And: when the load is mains-rated, you spend more time double-checking your relay wiring than being clever in software. That is a healthy ratio.

Honestly, the whole project was a lot easier than I expected.

Writeup

A short Norwegian writeup with photos of the light in each state lives in the repo:

Download: trafikklys.pdf (PDF)

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