Description

This clock is built with IV-9 numitrons. They operate at around 3-4 V and require approximately 20 mA per segment. There is no PCB in this project, hence the freeform style, and even the SOP-package driver ICs are soldered directly to copper wire.

I was strongly inspired by the projects of Mohit Bhoite, whose work is amazing.

Frame and Wiring

All wiring is done with 1.5 mm² copper wire for the structural parts and 0.75 mm² wire for more intricate electrical connections.

Electronics

Electrically, the clock is not very complicated. An ESP8266 is the main controller. I chose it because it supports Wi-Fi and gives me the option to display additional internet-based data in the future. The driver ICs are STP16DP05MTR constant-current LED drivers. This may seem like an unusual choice, but the current limiting (set to about 18 mA) should help extend numitron lifetime. Other high-current open-drain shift registers were similarly priced. I effectively wasted 8 pins per driver, but this made the already tricky assembly much easier.

The ESP is connected to daisy-chained shift registers and shifts out the current time. At the back of the clock there is also a small LDR read by the ADC, so the clock can turn off at night.

Results

I really like how the clock looks and how it turned out. I struggled quite a lot with soldering SMD parts onto wire and aligning everything reasonably well, but in the end it was worth the effort.