Single Vacuum Fluorescent Display Clock

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Vacuum fluorescent displays are display devices similar to nixie tubes, but they were designed for low voltage use. Vacuum fluorescent displays (VFDs) are basically like 7-segment displays with fluorescent-coated anodes/plates. A grid is placed between the dim filament in the front and the 7 anodes, basically a triode. When a positive voltage is placed on a segment, the fluorescent coating lights up greenish-blue. Inspired by my single numitron clock, I used a good VFD tube and made another single-digit clock. Below is a schematic of the VFD clock:

The clock is exactly the same as the single numitron clock except the clock program was converted for a common cathode display (the software is below). I used NPN transistors (not shown in schematic) for the VFD segments and 12V on the grid of the tube. However, the transistors are probably entirely unnecessary because the display came out rather dim. The PIC probably can drive the VFD directly without the transistors and achieve the same display brightness so the only basic difference is 12V being applied to the grid of the VFD tube. Also I used a 100 ohm resistor from 5V and two diodes to ground to obtain 1.4V for the VFD filament. I used four micro-sized red LEDs just under the VFD tube to indicate which digit is being displayed (HHMM) Overall, the clock keeps time nicely.

Additionally, the software and circuit can be used to drive a single common-cathode LED display rather than a VFD. The only difference is to omit the VFD filament circuit including the two diodes and the 100-ohm resistor.

The .ASM file is the PIC assembly program for the clock. The .HEX file is the assembled program used to program the PIC.

24 Hour VFD Clock (.ASM file)
24 Hour VFD Clock (.HEX file)
12 Hour VFD Clock (.ASM file)
12 Hour VFD Clock (.HEX file)

Pictures:

The Single VFD Clock

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