not for hire 

One of the coolest things I've seen in a long time is johngineer's ChronodeVFD project.  Unfortunately, he doesn't provide schematics or a lot of details about his project beyond a high level description of some of his design considerations.  He does mention some of the core components he used though:

  • Atmel ATMega88 (microcontroller)
  • Maxim DS3231 (real time clock)
  • Maxim MAX6920 (a shift register designed specifically for VFDs)
  • OnSemiconductor NCP1403 (DC-DC voltage converter)
  • IVL2-7/5 VFD display tube (Russian VFD, available on ebay)

The datasheet for the NCP1403 recommends a particular diode (MBR0520LT1) for use with the step up circuit, so I got a couple of those also.

Note that most of those components above are surface mount form factors.  The MAX6920 is a 20 pin (!) SOIC, so if you're not comfortable with that level of precision in soldering, it might be best to look for some larger form factor.  Being a masochist, I got the SOICs.

I suppose before I get started I should declare that my intention isn't to replicate the same wristwatch that he created, but to use similar components to come to the same end functionality.  For now, I'm going to use an arduino uno instead of the ATMega88, and rely on a wall wort rather than work in battery power.  I'm also going to try to go as simple as possible.  KISS policy in effect here.  I'm also learning as I go, and I'm not exactly an electrical engineer, more like a clever idiot.

So the first thing that needs to be done is to prove that the VFDs even work.  I mean, they're Soviet surplus that's just been sitting god knows where for the last 20+ years, so who knows?  I got a pack of 10 from my friendly Russian ebay dealer.  They arrived, box covered in customs stamps with the inside stuffed with Russian newspaper.  If I wasn't on someone's watch list before, I'm sure I am now.  :D

In order to be able to get any sort of reaction from the VFD, you need some different voltages.  The datasheets call for a filament voltage of 2.4V, a grid voltage of 24v, and an anode voltage of 24v.  You don't want to exceed them by much, but you can actually drive it at lower voltages fairly nicely.  I got a pretty good reaction from 3.3V (hot off the Uno) on the filament, and set up the NCP1403 to output @ 15.5V for the grid/filament:

What you see here is 3.3v on pin 1 of the breadboard, 15.5v on pins 2-15 (provided by the voltage converter on the right side) and then ground is awkwardly alligator clipped to the top of the VFD (the pins are fragile and I mangled the filament pin on the bottom while trying to plug it into the board).  That should be enough to get you a lit up display and confirm that yours works!

I'll be going into the pins on the VFD in further detail, along with talking about the voltage converter in the next post.