Large Nixie Clock

After the success with the first clock, I wanted to make something bigger. I have of course seen these large tubes with 30 mm or bigger digits and wanted to build something using tubes like that. My first idea was to use tubes like Z5680 (50 mm digit height), but the price and availability ruled them out. Instead, I found IN-18, a russian tube with 40 mm digit height that was easy to obtain and had a reasonable price.

This project is more than large tubes - I wanted to use a microcontroller to be able to have more functions and make the clock easier to use. The heart of the clock is a AT90S8515 and a realtime clock chip, DS1302. To avoid the problems with multiplexing the tubes but in the same time save at the uC ports, I construncted some discrete logics that buffers the display. A set of decoders and latches allows me to write the tubes in pairs with decimal numbers. The latches are connected to the drivers of the tubes.

The design got rather complicated so handwireing this was not an option. Instead real PCB's was ordered. Double-sided with solder mask and component layout. All to create a professional look and a reliable construction.

Schematics: download as pdf
Sources: code for the MCU and Gerbers for the PCB

Design images from the clock build:

The IN-18 tubes

Test firing one of the tubes

The PCB's fresh from the factory

Assembling the board

First dry run to test the drivers

All parts in place (first version without COM-port)

The clock is running

Clock complete with PSU

Wood (oak) case to match the tubes

Pictures of the final design