This is an email inbox counter, using a single IV-6 VFD tube.
I needed the other breadboard for another project, and I'm always looking to simplify and reduce things.
I have a new build of the VFD tube email counter which improves several aspects of the original:
- replaced atmega8 microcontroller with smaller attiny2313
- replaced IRF730 power mosfet with smaller IRFD110
- replaced $20 FTDI USB-serial cable with $2 PL2303 cable
- replaced boring old white breadboard with fancy new transparent breadboard
- replaced ugly breadboard wires with shiny magwire
However, by far the biggest change is the elimination of 7 transistors. The first design used the conventional high-side switch arrangement of a level-shifting NPN to switch a PNP driving each segment anode, but it bothered me that Jon Stanley was able to get his single-tube clock working without the level-shifting NPNs. Now, Jon's clock is operating at a lower voltage than mine, and he's using a PIC instead of an AVR, so I wasn't sure if I could make that work. It seems that compensating for the higher voltage with a bigger base resistor works just fine so far.
If it continues to work well, I'll put it on a circuit board and make a nice aluminum case for it, like this one.
The star of the show is the Soviet IV-6 vacuum fluorescent display tube, brand new from old stock. I picked it up on ebay for $1 delivered unit cost.
Digit segment switching is via 7 2N3904/3906 NPN/PNP transistor pairs. I didn't want to use a VFD driver chip because a) they are scarce/obsolescent b) they are expensive c) they are overkill for a single 7-segment tube and d) most don't have a thruhole package option anyway.
The section to the right of the tube is a boost converter circuit to generate the ~25V to drive the grid and segments. Since it is a single digit tube, it is a direct DC drive. The IRF730 power MOSFET is modulated by the PWM output of the Atmega8 on the left side of the board.
Power and communication is via an FTDI FT232R USB-serial cable, which I will replace with a cheap PL2303 cable (when it arrives from Hong Kong). I'm also gonna move this to one of those fancy new transparent breadboards, because I think that look will really complement the vacuum tube. I might rethink the layout to see if I can cut down on the tangle of wires.