IV11 VFD clock

published 11.03.2017

After I discovered these nice VFD tubes of the type IV-11 in the online shop of Ulrich Radig, I built a clock from it.

I used an ESP8266 board (nodeMCU1.0) as main processor and WiFi module.

For driving the VFD tubes a MAX6921 is used in this clock. An extremely convenient chip, with 20 push-pull outputs, which the chip can pull up to any input voltage (up to 76 volts). Controllable via SPI, allowing a very fast data feed via HW peripherals from the microcontroller of your choice. The only drawback is the price and availability of these chips.

The ESP8266 was programmed with the Arduino-Toolchain. This takes away unpleasant tasks like NTP handling, time zones and DST conversions. Only the MAX6921 driver had to be developed by myself, because to my astonishment there was no library for it yet.

The MAX6921 actually expects 20 bits, which are sent via SPI. A bit tricky is that the SPI interface of the ESP8266 (at least with the Arduino-Lib) only supports 8 bit transfers, so I don't get 20 bits. Fortunately, the chip has no problem with 24 bit (3 byte) data transmissions, the first and excess 4 bits are simply output at the DOUT pin.

The VFD tubes need 2 voltages, 25V DC for the anodes and grids and 1.5V for the heater. Fortunately, both voltages can be generated easily, accurately and efficiently using LM2587 step-up or step-down modules.

The ESP8266 makes an NTP sync every hour via a configurable time server. The code can contain several pairs of SSID and PSK for different WLAN networks. The controller automatically selects the strongest SSID.