The row of 6 nixies has been proven to work using the Arduino scrolling sketch. I wanted however to ensure that they were ready to put to work. (Except for finding a suitable enclosure, this is a perennial bugbear of mine. The bamboo box in the picture is not suitable, it gives no protection to the nixie tubes.)

So I connected them up to a CH552 board, one of two I use a CLI toolchain to program. I have to say they are very easy boards to download firmware to, only a USB-C cable is needed, but you need two hands, one to hold down the BOOT button and the other to plug the USB cable into the computer port. You can see the CH552 module at the right, with the yellow pin headers. The other board is the power supply.

The firmware is in fact the same that I developed for driving #Ancient 12 hour display with a different ifdef sections activated. I only found one extra bug, if you can call not behaving like I wanted: the seconds digits were still active when setting hours; they should be blanked.

There was unexpected behaviour; the hours decimal point would only blink when setting minutes where the hours were blanked, and also for about 5 seconds after returning to normal display mode. I looked over my code many times, then finally realised that as the decimal point cathode competes with the digit cathodes for the ionisation path, it could only work when no digits are lit, and perhaps for a few seconds after returning to normal display mode. So it's an inherent limitation. Anyway the blinking decimal point is redundant; the changing seconds digits will indicate that the clock is running.

Ok, now I can take this project off my list of old-fangled stuff to use up. It's also goodbye to the CH552s; I'm moving on to RISC-V MCUs.