VFD Alarm Clock

IV-27M Alarm Clock

Project date: March 2019 – May 2019


After the successful completion of the XIV Nixie Clock which was Direct/Static Driven, I was keen to start work on a new clock which was based on the Multiplexing(Dynamic) or “MUX” principle of operation, known also as “Muxing”. The new clock would be based on the USSR manufactured IV-27V VFD, 13 element, 7 segment tube. This tube requires a 24V common anode DC supply, which dictates what type of IC chip(s) are needed to support the multiplexing operation. To further understand multiplexing the following Wikipedia articles where of great help:


To understand how VFD displays work and what is involved in driving the display using either Direct or Multiplexed driver the following article was very useful:


The clock would have a simple function of displaying Time, Date, Humidity, Temperature, Pressure and an Alarm feature..

Here is a brief summary of how the IV-27M tube works:

The tube is evacuated (vacuum). In the tube is a substrate (anode) (usually based on phosphorus), which begins to shine when “bombarded” with electrons.The electrons come from a heater (cathode), which are in the form of very thin tungsten wires. Between the substrate (anode) and the heater (cathode) a control grid is mounted which is used to turn on and off the individual elements. The tube used here consists of 13 seven-segment displays.

The tube was manufactured in Russia in 1985 and carries the Russian Quality production mark on the rear of the tube. Both tubes I purchased came from an Ebay supplier “nixiestore” who I would highly recommend.


1. Arduino Mega 2560

2. MAX6921AWI Chip

3. TSSOP28 PCB board, 28 pin connection

4. IV-27M Russian 13 grid, 7 segment tube

5. BME280 sensor

6. 3W speaker

7. 16×2 LCD display with IC2 connection board

8. Green LED with 330 ohm resistor

9. RTC clock with battery backup

10. 12V to 3.5V Step Down DC-DC Adapter

11. 12V to 24V Boost DC-DC Adapter

12. 12V, 1A power Adapter

13. Two pole switch

14. 16 key keypad

15. Hot Glue, wood for box, felt feet, clear gloss varnish.

16. 30 AWG multi-coloured wire, heat shrink, PCB female connections.

17. Dupont connection wires

18. Plastic stand-offs for support of components

19. Arduino Board two pin Power Input plug

20. Small PCB board and two sets of header pins

Step 1: Pin Assignment of IV-27M


Cathode Heater Voltage

It is very important to use 3.5V. There have been some references to using 5V on the internet. While this could be used it will over-heat the grid heaters. To see this in operation view the IV-27M tube, while it is working, in a darkened room, the two heater lines can clearly be seen glowing red!


The first part of the project was to determine the pinouts on the IV-27M tube. There are Russian language-based datasheets and numerous Internet based descriptions of the left and right pinouts. Looking at the tube with the digits facing you, the left hand end has 15 pins and the right hand end has 11 pins. I simply soldered coloured 30 Gauge wires to both ends terminating in Dupont breadboard pins. Six of the left hand wires and one of the right hand wires had black heat shrink bands added to each end in order to differentiate them from the other solid colour wires.

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