The VFD and PWM drivers:

For the management of VFD tubes, I used a specialized circuit: The MAX6934.

It allows controlling up to 32 grids / anodes via a serial interface.

It allows to use a voltage going from 8 to 76V. It is possible to put several in series.

For this application, all outputs are used (4 x 7 anodes + 4 x 1 grid).

There are circuits with fewer outputs in the same family of components at Maxim integrated.

The tubes are mounted on small supports which are perfectly suited for their mechanical support and to compensate for the height of the LEDs.

These are spikes that I recovered several years ago and I can’t find the same ones. If you have a source please let me know  

For the management of RGB LEDs, I chose to use a PCA9685 circuit from the manufacturer NXP.

I have already used this circuit in several projects: The RGB clock and the Christmas tree.

It can control 16 LEDs in 12-bit PWM via an I2C bus. In this application 15 outputs are used (5 LEDs x 3 colors).

The LEDs are coupled to a MOSFET transistor.

This allows the LEDs to be supplied with 12V and does not increase the current consumption at the output of the 5V regulator.

Warning ! The LEDs are in common anodes.

The seconds LED was mounted on two LED supports. These are the same ones I used on the RGB clock. They had been bought on ebay.

The sensors and their amplification:

The clock has two sensors: a light sensor and a temperature sensor.

The light sensor makes it possible to detect a drop in light and to be able to turn off the LEDs at night (to avoid light pollution).

A setting option allows the management of the LED lighting. Three modes are available (see video).

The light sensor used is a photoresistor. It is mounted on a voltage divider bridge then amplified via a non-inverting AOP circuit.

The non-inverting assembly has a gain of 2.

The output of the assembly is connected to an ADC input of the microcontroller.

I’m going to add a setting to the clock so that I can adjust the detection level because it depends on where it is located.

The temperature sensor used is an LM35.

It has been placed opposite the power supplies to avoid disturbing the measurement in case the power supplies heat up.

The non-inverting assembly has a gain of 4.9.

The output of the assembly is connected to an ADC input of the microcontroller.

The sensor output voltage is proportional to the temperature (10mV per ° C).

This assembly can therefore be used for a temperature range from 0 ° to 100 ° C.

The sensors have been mounted with an LED support for their mechanical support. I used the same as on the seconds LED.

 The PSTN circuit:

The RTC (real-time clock) circuit allows real-time clock management. It stores hours, minutes, seconds …

The circuit chosen is a PCF8563 from the manufacturer NXP.

VFD clock of Etienne | October 20, 2019 | VFD2 Tube Clock Project Comments

I present to you my finalized “VFD Clock” project.

Through this article, I will explain the electronic functioning of the clock and the VFD tubes that I used on it.

Good reading and see you soon to see the rest of my current projects  

To start, here are some pictures of the set:

1] VFD IV-12 (ИВ-12) tubes:

The VFD (vacuum fluorescent display) tubes that I selected for this clock, are displays that were used in the 80s.

They have the particularity of being very resistant to cold. They were used in particular in the USSR.

It gives them a second life and I find them beautiful.

You can find them for purchase on ebay. Sellers are often found in Russia or Ukraine.

These displays consist of a heated cathode (filament), anodes and a grid. The whole is sealed in a glass envelope where there is a high vacuume.

Their operation is quite similar to a triode (with direct heating). The heated cathode allows the release of its electrons from its support.

The grid makes it possible to favor or restrict the passage of electrons, this in particular makes it possible to be able to make multiplexing.

When the grid and an anode are at positive potential, the electrons strike the fluorescent part of the controlled segment.

2] The electronic card

As mentioned in the previous article, I tested the services of the PCBWay site for manufacturing the PCB.

I had no problem except for the holes in the power connector but I realized that the GERBER was not very clear about it

So I did the drilling with my mini drill (dremel), as it is double-sided no problem to do so.

GERBER files are available at the end of the article.

Photos of the card before and after welding of the components

I made clocks a few years ago with a PCB made by myself.

I provide the files at the end of the article so that you can make it easier


This clock includes:

a PIC18 microcontroller

four VFD tubes

a VFD driver

five LEDs

a PWM LED driver

three power supplies


a backup battery

a light sensor

a temperature sensor

two operational amplifiers

four push buttons

2] Power supplies:

For this application, you must integrate:

a 5V power supply for the microcontroller, the RTC and the operational amplifiers.

1.5V 500mA power supply for VFD cathodes

a 30V 150mA power supply for the anodes and the grid of VFD tubes

The 5V supply is made by a linear regulator in a SOT89 box.

It is not easy to create a 1.5V power supply with an output current of 500mA. This current consumption is due to the power of the 4 cathodes (4 x 110mA max).

I chose to use the MC34063 circuit which is very suitable for doing this. It is configured in “step-down” mounting.

For the 30V power supply, I chose to use the same circuit. It can also be configured in “step-up” mounting.