1U rackmount clock

Clock module with dimmable output for a 12V rack light

In my mixer case I had exactly 1U free. To fill up the free space with something useful I made this small clock module.

Picture: Front side of the board

The central controlling is done by an Atmel ATTINY2313 microcontroller. It gets its time from a DS1307 RTC. The display of type FIP5Q13 comes from my tinkering box and is driven by the VFD driver combination of MAX6921 / LM9022. These two chips were also used in my talking alarm clock.

Picture: Backside of the board

The real-time clock is not yet assembled, but it is not necessary for testing the vacuum fluorescence display.

Picture: Testing the display

The firmware is written completely in C. To set the time, simply press the button on the back. With the rotary encoder, hours and minutes can be set. Furthermore a PWM dimming function for the LED rack light is implemented. The desired brightness can be set in 25 steps. Besides the setting mode, the rotary encoder is used for the brightness control. The selected brightness level is also shown in the display, for example LA15. The set brightness value is stored in the EEProm and is thus permanently stored. After a few seconds the display changes back to the actual time.

Picture: VFD color filter

To protect the display and to increase the contrast, blue acrylic glass is mounted in front of the VFD.

Picture: Test run with bezel

Lutz has sanded the bezel for me and then machined it on the CNC mill. The corners in the display cutout were then carefully filed by hand. (These are usually a bit round depending on the size of the milling cutter) Afterwards I had the bezel painted black matt. Whow!

The acrylic glass plate in front of the display is glued with silicone. To fix the display I used my favorite two-component glue Pattex Stabilit. Underneath the glue, the paint had to be sanded away with the Proxxon until bare metal was visible. M3 screws are used as spacers.

Picture: Glue

When installed in the case, the whole thing looks like this:

Picture: Clock in the case

The clock has been running since 2009 without any problems!


In 2022, a suitable back cover was created. It was drawn using OpenSCAD and 3D printed.

Screenshot: Enclosure in OpenSCAD
Picture: Finished enclosure

Unfortunately there is no schematic for this project. The display is also a unique piece. If you want to rebuild this clock anyway, you are welcome to modify the source code to another VF display.