This is a quick and simple clock board based on a STM8 development module. It uses a TCXO DS3231 module for accurate timekeeping. Later a #3 line to 32 line output expander module for driving the nixies in #Repurposing an old nixie thermometer will be connected. For testing, a TM1637 module with alternate firmware is used.

There is so little wiring that I built it on double-sided perfboard with plated through holes. I drew the schematic in KiCad and generated a board so that the positions of the modules, switches, connectors, resistors, and wires could be plotted for soldering. It was even possible to route it using only the bottom copper layer by putting a keepout zone over the top copper layer.

For flashing the firmware the 3V3 jumper is removed while for operation it is replaced to run the MCU at 5V. However I found that when plugged into the board socket, the module cannot be flashed. To do this I have to unplug it from the board. I haven't looked for the cause as it's just a small annoyance at the moment.