I finally completed casing my scratch-built Classic Rev4 6-Digit clock.
Using the schematic, I built the circuit up on prototyping strip board. I left off the high-voltage circuitry in favor of an old-school iron transformer approach. I used two 120VAC <> 18VAC transformers connected back-to-back for line isolation. The secondaries had a number of windings. I connected a few in buck/boost configurations to get 130vac on the output of the second transformer. I fed this to a simple bridge rectifier and capacitor-filter to produce a no-load voltage of about 130 x 1.414 = 184VDC. This sags a bit under load to about 178 volts with the Nixies lit. Of course this approach would work with identical transformers only in countries with 120VAC line voltage or similar, but it does make it easy to make a Nixie power supply.
An additional tap off of the first transformer is rectified, filtered, and used for the regulated +5VDC for the Atmega328p.
The high voltage generation and calibration happily ignores that I am using an external power supply and completes it's initial calibration normally without affecting the HV output at all.
I wanted to add in WiFi capabilities along with the RTC module. I purchased an ESP8266-based NodeMCU ESP-12E development board with built-in USB interface and voltage regulator. I mounted this to a satellite board along with a 3.3 <> 5 volt level converter for the SDA and SCL I2C signals. Even though this is a v1 clock, I found the v2 NTP time source WiFi module code worked fine with the latest firmware, after I tracked down and fixed a few bugs in the code that corrupted the time zone setting when the time values were retrieved from the SPIFFS filesystem on the ESP8266. I also changed the I2C SDA/SCL pins to avoid conflicting with internal circuitry on the ESP-12E board (mostly on-board LEDs).
I mounted it into an old loudspeaker case. The pulsating seconds LED is mounted on the clock top in front of the tubes, next to an adhesive membrane push button switch for manual control. The LDR is also mounted on the case top for brightness control. A single jumbo RGB LED is mounted behind the speaker grill for clock setting feedback and a soft night light.
I programmed the Atmega328p by extracting the Intel hex file from the Arduino IDE temp directory and burning it to the chip with a Minipro programmer. I selected some appropriate fuse setting for an external 16 MHz crystal clock and reasonable brown-out reset values.
The build is huge and clunky compared to my other Nixie clocks, but I rather like the look. The WiFi module runs well with v2 code. The official v1 WiFi code does not yet support NTP time sync.
Thanks, Ian, for making the hardware and software open-source. I had great fun building it!