AgriVision's IO Extender Boards Bring I2C Connectivity to Classic Nixie Tube Displays

What do you do if you find an Electromatic EZK six-digit Nixie tube display in the attic? If you're AgriVision, you get to work in interfacing it with a microcontroller — using a clever custom IO expansion board design.

"Currently there is a lot of interest in bringing vintage Nixie tubes to life," AgriVision writes. "Lots of Nixie tube clock kits are available on the market. There appeared to be even a lively trade on old stock of Russian Nixie tubes. This Instructable describes a driver for Nixie tubes with IO extenders, controllable by I2C, using a versatile PCB developed specifically for this purpose."

The Nixie tubes in question are part of an Electromatic EZK six-digit display, discovered during an attic clear-out — alongside, handily, its documentation. While AgriVision's project concentrates on converting the Electromatic EZK specifically, the resulting board design is compatible with any Nixie tube displays which use the same SN74141 TTL drivers.

"I was quite happy when I found this device," AgriVision writes, "and my first thought was to make a clock out of it. In the end I made a versatile display device, based on an Intel Edison, for displaying time, date, temperature, humidity and even the number of likes of the projects blog."

To act as an interface between the display and the microcontroller, AgriVision needed a custom circuit. "The 7490 BCD counters must be removed, and for each two of them replaced by one PCF8574 IO extender," he explains. "For this counter three IO extenders are needed, interconnected with I2C and connected to a control device. Luckily all ICs are placed in sockets, so the replacement circuit can be inserted in the 7490 sockets."

AgriVision's full guide is available on Instructables, while the board design files are available on GitHub under the GNU General Public Licence 3.0. More information on the project can also be found on the element14 community site.