Nixie Clock 2

After completing Nixie Clock 1 over a year ago, I still had an extra set of IN-12B tubes that were not being put to good use. Time to build another one. Actually, I ordered yet more tubes and driver ICs so I could build 3 more.

The basic design is almost the same as Clock 1: Russian IN-12B with a K155D1 driver for each tube, shift registers to run the drivers, and this 180V power supply design. A DS3232M is provided for the RTC. There are a few changes; remembering some lessons learned when I built clock #1, I made the following list of improvements:

• Simpler (or no) sockets. Most of the time towards building the first clock was wiring the 72 pins on the tube sockets. If I could somehow avoid doing that, it would save me lots of time. I ended up using pins from cheap DB25 connectors, which when taken apart get you 25 connectors which are the perfect size to accept the IN-12 pins. I'm not the first one to think of this, and I used an Eagle pattern that I found for the IN-12 Nixies, but the same idea might work for other tubes also. The female PCB mount version of the China DB-25 connectors are what I used, although the Eagle pattern I used accepts the pins a little farther up on the shoulders of the pin, rather than on the section designed to mount into the PCB, so that part is clipped off. Also of note is that the pins are made of stamped flat metal, not a solid chunk, so solder will flow into any holes and fill in the inside of the tube. Therefore, it is important not to use too much solder.

• PCB for components. After designing some PCBs for some of my other projects, I realized that it really isn't that hard to design a PCB. It makes everything smaller and neater, and cuts down on assembly time. To maintain a compact design, I designed 2 "stacked" PCBs: one has the power supply, microcontroller, RTC and drivers, and the other holds the tubes. I could also possibly change out the carrier board if I ever want to experiment with other tubes.
• Some kind of case (3D printed) which is easily replicated and doesn't require many hours of hand filing like Clock 1.
• ESP8266 powered. This would give Internet access, and I could also use UDP for some remote control features instead of an IR remote, which would allow greater flexibility when interfacing with other projects, as I have always intended for these displays.

All said and done, I came up with the solution you see here (or, at least you will once I add pictures).

I made a couple mistakes in PCB revision 1: a missing resistor on the I2C bus, and trying to use GPIO15 as the shift register latch pin, without realizing the logic level converter I made pulls it low on startup, not allowing the ESP8266 to boot. I fixed this by cutting the trace and attaching it to another pin.

Software

To make the PCB design easier, I drive the tubes "out of order", so I need to shift some bits around before the display comes out looking right. Here's the routine I came up with. It isn't very elegant but gets the job done.

void nixie(long k, byte dp){
  byte dig0=(k%10);
  byte dig1=(k%100)/10;
  byte dig2=(k%1000)/100;
  byte dig3=(k%10000)/1000;
  byte dig4=(k%100000)/10000;
  byte dig5=(k%1000000)/100000;
  byte dots=((dp&0b00100000)<<2)+((dp&0b00010000))+((dp&0b00001000)<<3)+((dp&0b00000100)<<1)+((dp&0b00000010)<<4)+((dp&0b00000001)<<2);
  shiftOut(srDataPin, srClockPin, MSBFIRST, dots);
  shiftOut(srDataPin, srClockPin, MSBFIRST, dig0*16+dig1);
  shiftOut(srDataPin, srClockPin, MSBFIRST, dig2*16+dig3);
  shiftOut(srDataPin, srClockPin, MSBFIRST, dig4*16+dig5);
  digitalWrite(srLatchPin,LOW);
  digitalWrite(srLatchPin,HIGH);
}

Files

• File:Nixie2-hardware.zip - Hardware files - PCB and STL for case