Continuing my unstoppable obsession with clocks, I built another one this summer based around a vacuum fluorescent display I found at Excess Solutions (one of the many local bay area electronics salvage stores). VFD's are pretty cool, because instead of having each segment be an LED in typical displays, a series of wires and meshes are used to shoot free electrons at a phosphor, which then creates the light you see from the display.
Ice Tube clock, which drives a VFD (along with a much more developed interface than any of my clocks...). Lady Ada is kind enough to publish all of her kit schematics, so why try and figure out how to drive the display myself, when she's already found a functional solution?
This solved two of my problems. It turned me onto the MAX6921 VFD buffer chip, which is the shift register and the voltage buffers combined in one chip, and it gave me the circuit I needed for the charge pump to step the 5V coming from my power supply to the 40V needed to light the VFD segments. Thanks LadyAda!
breakout board from Electroboards. This means I can now feed 40V and 5V logic signals into the MAX6921 buffer to drive the VLD.
Schottky diode to a high voltage capacitor. This is called a boost converter. Feel free to hit Wikipedia for a better explanation.
The rest of the clock is a fairly typical DS1307 talking to an ATTiny2313, which then multiplexes the digits of the VFD at 300Hz.
Source code listing at the end of the post!
So how do VFDs work?