Automatic aquarium lights

My aquarium plants were dying because I kept forgetting to switch the lamp on, and the cheapest smart light was ¥19,000. With no hardware experience at all, I built one myself.

I wired a Raspberry Pi 4 to an opto-isolated relay, added a DS3231 clock so the schedule runs without Wi-Fi, and sealed the fused mains side in an ABS case.

Two weeks later the tank was the greenest it has ever been. It cost ¥22,730, more than the ready-made light, but I understand every wire in it.