Homebrew VFD – A maker built a compact vacuum fluorescent display clock powered by a single AA cell, using an ATmega328P microcontroller, a 32.768 kHz crystal for precise timing, and a high-voltage driver to keep a harvested calculator VFD lit.
The clock face doesn’t look like a typical electronics project. It’s a vacuum fluorescent display pulled from an old calculator, lit up with voltages that are usually the headache in builds like this.
But in this homebrew effort, the hard part got turned into the point. The clock is built around an ATmega328P microcontroller running from a 32.768 kHz crystal. That setup lets its counters divide down the crystal frequency to produce a steady 1 Hz pulse for timekeeping.
Time appears on the VFD, and the display brings its own demands: VFDs require rather high voltages to run. Here, those voltages are produced by an HV5812 driver chip and supporting circuitry.
The maker didn’t leave the hardware exposed either. The VFD is cradled inside a pair of copper pipe elbows, giving the clock a small, industrial kind of charm. Underneath, addressable RGB LEDs are included to provide a soft underglow.
Power is where this build makes its boldest claim: the device runs on a single AA battery. A transformer-based low voltage converter handles the draw. There’s also a second option for day-to-day use—running the clock off a USB 5 V power supply. When connected to USB, the setup charges the NiMH AA cell, using an LM2576-ADJ buck converter while available.
The project comes with a practical message beyond the gadget itself: it’s a reminder that older display tech still has a lot of life left in it. It’s also not the first time someone has built a clock using second-hand VFDs. and the builder notes that the construction taught them plenty along the way—another quiet reason these tinkering projects keep resurfacing.
If you’ve got your own ideas for reusing legacy display hardware, the maker is asking for tips—because the fun, apparently, is in the reuse as much as the result.
VFD clock ATmega328P 32.768 kHz crystal vacuum fluorescent display HV5812 single AA battery USB 5 V charging LM2576-ADJ NiMH maker project