Kindly Morrow
6-Tube Digital Nixie Clock
Six IN-14 Nixie tubes, glowing orange at 170V, driven by a high-voltage shift register you wire up yourself. Solder it in an afternoon. Modify the firmware the same night.
The driver board pairs an HV5122 32-channel HV shift register with a K155ID1 BCD-to-decimal decoder to select cathodes per digit. A built-in boost converter takes 5V USB input and steps it up to 170V DC, keeping all the high-voltage work contained to the board. A DS3231 TCXO-backed RTC holds time to within 2 minutes per year, and the ATmega328P comes pre-flashed so the clock runs the moment you power it on.
Things to build with this
- Use the HV5122's SPI PWM control to build a Pomodoro timer that ramps tube brightness down gradually during a 25-minute work interval, then pulses all six tubes in a slot-machine spin on the break transition
- Wire an ESP8266 to the exposed SPI and I2C headers, pull NTP time on every boot, and write a drift-correction routine that uses the DS3231's aging offset register to trim the TCXO calibration over time
- Replace the default ATmega328P firmware with a CO2-responsive display: connect an SCD40 to the I2C header and map live ppm readings across the six digits, using the per-digit cathode control to blank leading zeros and flash tube 6 as a threshold alert above 1000ppm
Key Features
- Tubes: 6x Soviet-era IN-14 Nixie tubes, orange neon glow at 170V operating voltage
- RTC: DS3231 with TCXO, ±2ppm accuracy, CR2032 battery backup for timekeeping through power loss
- Driver IC: HV5122 32-channel high-voltage shift register, SPI interface, PWM brightness control from 0-255 in firmware
- Decoder: K155ID1 BCD-to-decimal for individual cathode selection per digit
- Boost converter: onboard PSU steps 5V USB up to 170V DC, fully self-contained on the driver board
- MCU header: 5V logic header exposes SPI, I2C, and interrupt lines for swapping in an Arduino Nano, RP2040, or any 5V-tolerant MCU
- Enclosure: 3mm laser-cut acrylic panels, pre-drilled, stacks on four standoffs with no machining required
Frequently Asked Questions
Is working with 170V safe for a kit builder?
The high voltage is present only at the tube pins and the boost converter output, both of which stay on the driver board. Power down before probing, use insulated tweezers near the tube sockets, and follow the build guide's sequencing. Standard kit precautions cover it.
Can I swap out the included ATmega328P for a different MCU?
Yes. The SPI and I2C headers are broken out on a 5V logic header, so an Arduino Nano, RP2040, or any 5V-tolerant MCU drops right in. The HV5122 just needs SPI and a latch pin. The DS3231 is standard I2C.
How do you prevent cathode poisoning on the IN-14 tubes?
The default firmware runs a slot-machine cycling routine that steps through all ten cathodes on each digit periodically, keeping every cathode active. If you write custom firmware, build in your own cycling routine. Leaving a single digit static for thousands of hours is what causes poisoning.
How long will the IN-14 tubes last?
IN-14s are rated at roughly 150,000 to 200,000 hours. At 24/7 use that is 17 to 22 years. Cathode poisoning from static display is a bigger practical risk than tube burnout for most users.
Why we stock this
Curated by Kindly Morrow. We test and vet every product before it hits the store. If we wouldn't use it in our own builds, we don't sell it.
Things to build with this
Fun projects to try once you get your hands on it.
Split-flap board connected to Claude
Hook up a display to the Claude API and have it show you a new message every morning. Motivational quotes, weather, or passive-aggressive reminders to drink water.
Spotify now-playing display
Shows album art and track name on your desk display. Updates only when the song changes. Zero battery drain between updates.
Real-time crypto/stock ticker
Pull prices from an API, show them on the display. Flip between assets. Try not to check it every 30 seconds.
Ambient room dashboard
Temperature, humidity, air quality, and time on a bedside e-ink screen. Updates every 5 minutes, uses almost no power. Looks like a museum label.
