Nixie Clock – ing DIY

This is a Nixie tube clock that combines the charm of vintage technology used until the 1940s with modern circuit solutions based on a microcontroller. The heart of this system is an ATXMEGA128A3U microcontroller running a state machine firmware. The CPU controls the Nixie tubes brightness through high-voltage shift registers connected on the SPI bus.

In addition, the microcontroller interfaces with an HD44780 display, through which it controls brightness using PWM and contrast via a digital potentiometer. Furthermore, a DAC output from the CPU is connected to a preamp with a second-order Butterworth filter, which is then linked to a small amplifier for reproducing the alarm sound.

The task of keeping the time updated is entrusted to a highly accurate RTC (Real-Time Clock), which is backed up by a supercapacitor.

First prototype

The initial development phase involved creating a functional homemade prototype PCB. This prototype allowed testing of the DC-DC boost converter, high-voltage shift registers throughput, the connection with the HD44780 display, and the audio analog circuitry.

Assembling Electronics and Mechanics

After checking the functionality of the various circuit parts using the functional prototype, I proceeded to create the final PCB and had it manufactured by a supplier. Subsequently, I soldered all the components following the Bill of Materials (BOM) and the assembly instructions.

I designed the case using a 2D CAD software and created views with the holes and milling details to be applied to the case. I then produced templates on which I printed the 2D views with their respective holes and milling instructions for the case. Afterward, I began the manufacturing process.

Testing the Firmware

I did firmware test to verify the functionality of the LEDs that separate the digits of hours, minutes, and seconds. This helped me decide the type of animations to implement for the LEDs.

I wrote a test routine to verify the operation of the LCD contrast control, implemented through a digital potentiometer. This allows the CPU to have 0-100% LCD contrast control.

The clock is working

The Nixie Clock is finally operational. I’ve also programmed transition effects every time a digit returns to the ‘0’ value. Here’s what happens… at the stroke of midnight!