Nixie Wrist Watch, 4 Digits

This project is about making a 4-digit nixie wrist watch.
https://youtu.be/MAw0OgJxuy0

small size nixie tubes (4)
Arduino pro mimi

IC 7805
IC 555
IC 74141 (or 7441)
MPSA42 Transistors (5)
MPSA92 transistors (4)
RTC module DS3231
IRF740 mosfet
UF4007 diode
33 kohm resistors (5)
22 kohm resistors (4)

100 kohm resistors (5)

10 ohm resistor
1 kohm resistor
10 kohm resistors (4)

470 kohm resistors (4)

5 kohm potentiometer

100 nF 600V capacitor

100 pF capacitor

2.2 nF capacitor

100 uH 1A inductor

Lithium polymere batteries 300 mAh (2)
On/off switch
Push buttons (2)
Female jack (smallest size)
Charger adapter (8.4 volt, 1A)
3D printed case
Watch straps

With the schematic circuit offered here, the watch can run at least one hour in continuous display on.
Accuracy is better than one second in a year.

Try to use smallest components that is available (smd is preferred).
The RTC module must be very small size.
Assemble the parts on "air" to reduce the space.
More technical explanation on driving nixie tubes is available in my previous instructable (6-digit nixie clock)
https://www.instructables.com/id/6-Digit-Nixie-Clock-Timer-Thermometer/

In order to minimize the components and size, I have not included a charge control in the design. If the batteries are fully discharged, use 8.4 volt charger for about 4 hours (display off). Disconnect the charger after complete charge to avoid damage to the batteries.