Working in collaboration with Richard Scales, the result is a modular design clock board that utilises plug in units. The main module is a Wemos D1 mini with an NCH8200, BMP280, a 12v to 5v step down voltage regulator and some good old fashioned TTL chips.
This design developed from Richard's breadboard lash up to it's current format after a bit of banging and chiselling to get it to where it is. The Rev 1.0 had to be modified to accept more than one type of voltage regulator and have some voltage test points added as well as some cosmetic upgrade.
The PCB work I did in EasyEDA and Richard designed tube boards for remote mounting. To encompass various tubes all that is needed to be done is to alter the anode resistances and tweak the HV output to suit. PCB size is approximately 3" x 4".
Richard wrote the software on the Arduino platform as libraries can be added to the Arduino IDE for the Wemos D1.
I took the basic design and made a circular version of the PCB that has tube boards for IN-18s, ZM1040s and any other B13B mounting Nixie including top view ones. Just waiting on them arriving to get a prototype built with IN-18
This is an old screen grab as the main board has been modified a bit since conception.
You are right with the 74HC595 and the other two are 74141s. The opto base is for 2 x PC817s that are PWM'd from the Wemos D1, switching the output of the NCH8200.
As to decoupling capacitors, the breadboard version runs without them but I have no idea if they are required as that is Richard's side of it.
A Rev 1.0 runs OK based on the current programming but Richard has upped the performance with a revision that is newerer and betterer! It takes into account time zones, DST and a better technique for syncing to internet time.
If it works on a breadboard, it will most likely work better on a PCB...
The decoupling caps are there to deal with transients, noise and other disturbances which can make your circuit have transient or otherwise unexplainable errors. It is a bit of a black art, but it is usually a good idea to look back at the data sheets and see the reference designs to see if you should include one or not.
I always include one for each 74xx device (although HC and HCT are less troublesome) and some smoothing caps around the controller. Usually one large one (100uF+) and one small one (100nF).
100uF cap goes bewteen Vcc & GND, physically close to the microcontroller if practical. The 100nF filters out high frequency switching transients on the Vcc rail. The 100uF filters out lower frequency crud.
Terminology varies from person to person but in general, the 100nF cap's role is "bypass" or "decoupling" capacitor. The 100uF cap's role is "filter" or "smoothing" or even "reservoir" capacitor.
Look into it later when the dust is clearing off the crater.