The clock is based on an STM32F042 microcontroller for several reasons:

• It's in a small but still hand solderable package, ssop20.
• It has enough IO's for this project
• It has a build in USB bootloader, so no USB to serial converters or programmers needed.
• It has a build in RTC and crystal, so no external RTC components needed.

The second major component is the numitron driver, and 4 of them to be precise. I picked the TLC5916. (or TLC5917 if that one is easier to get) This has several reasons:

• Numitrons work best with a current of 20mA, just like an LED. This is something the TLC5916 is designed to provide.
• Simple SPI like protocol that supports chaining several together, just 4 IO's required in total.
• Possible to control the current, making dimming the displays possible.
• Available in an easy to use SOIC package.

4 buttons are used to set the time of the clock. These are nice and orange to match the tube glow.

The rest of the components are basic jellybean things; An LM1117 3.3V regulator to power the microcontroller, several 100nF decoupling caps, several 1K pullup resistors, a 1K resistor per TLC5916 to set the current to 20mA for the numitrons and 2 buttons to reset the uC and set it in bootloader mode.