06 December 2016

Nixie Tube Ciapapuer - 1

Or, in plain English, "Nixie tube home decor".

Literally: "Nixie tube dust collector."

Why, why would I ever want to build a device with just one Nixie? First of all, to use symbol Nixies like ZM1001 (side view) and B5094 (top view). Then because: housing is simpler than using several tubes, firmware is pretty simple (no RTC or strict timings), circuit is simple, it will result in a compact object.

My first attempt is with a ZM1001 that has 6 symbols, so there are 6 cathodes to switch. The typical 74141 driver has 10 outputs, nevertheless since I am lazy I choose it for this project, thus reducing the connection to uC to 3 data lines.

In order to differentiate from my previous projects and learn something new, this ornament firmware will also:
  • randomize transitions and next symbol
  • fade-in/fade-out
Fading requires one more control line. One way is to PWM the anode voltage through a PMOS or PNP: this requires a component with high Vds/Vce (that is missing in my junk box). Another way that is doable in this project is to switch the BCD combination to unused 74141 outputs. Either way uses a 4th output from the microcontroller, but the latter is "low voltage" and implemented in the basic circuit "by design."
So, going for fading through switching to unused outputs, a look at the 74141 truth table indicates that I can use the MSB (Most Significant Bit) to switch over to unused outputs (8, 9). Indicentally I had not planned to use those outputs, so now it is a matter of writing the proper software routine.