Cyberpunk Looking Nixie Watch with CNC Milled Chassis, Not-so-robust code, a microcontroller and one lazy student :)
#WIP
Z5900M(or Z590) Nixie Tubes are small Indication Tubes That require 150V DC(but with a measly 1~1.5mA Power Consumption) as a Power Source. It's small footprint and relative abundance compared to some Burroughs Tubes is curtainly a plus. There are Z5900s, they are the same ones with protective orange layer. You can get something like IN-16s for cheaper price but it is much taller(~10mm), and it does not have LHDP(Left-Hand Decimal Point) and RHDP(Right-Hand Decimal Point) so you would need additonal Neon Bulbs like INS-1 or use a Orange 0603 LEDs.
Since the entire project revolves around Arduino IDE - an AVR Friendly IDE - I used an ATTINY. Specificially, ATTINY- [] It's an ATTINY with Watchdog, Interrupt, I2C Capability, Plenty of I/Os, and Internal Pullup, and whole nine yards.
There are many ways to control these Nixie Tubes, including Russian made BCD to Decimal Decoder, K155ID1(Known Alias : SN74741). This one uses 4 BCD Pins to decode it into 10 Pin Decimal Pins. But it's large DIP-16 factor simply detered me, plus I would need a Optocoupler or a Second K155ID1 for a second tube, not even counting an AMPM Bulb in RHDP of Z5900M
There's where Microchip's HV5523 Comes in. It's essentially 74HC595 Shift Register - in fact we use that very library in arduino - but it has Open Drain meaning without it powered it can act be disconnected from the circuit, and ties connected pins to GND when it is. This way an Anode of Nixie Tube will be Connected to 150V Power Supply, and Cathodes will be connected to HV5523's HVOUT Pins.
First, we need to make an unstable voltage from Lithium Polymer(from charge to nominal it will vary from ~3.65v to 3.95v) and make it into relatively constant, 5V. An MCP74831 Circuit will do that for cheap and relatively easy. -- Battery Gauge to be added --
Then, we need a High Voltage Transformer that will pull this 5V into Healthy 150v. ElectroNoob recently did a video about this, so here I will use his design but change a variable voltage into single voltage, by simply replacing variable resistor into a normal resistor.