With the old dissected. Next step to brainstorm what to change for a new design

BCD over Binary

BCD Binary clocks are a bit more common than regular. But reading 0-9 decimals from 4-bits is way easier and faster than deciphering a number from 0-59 from 6-bits. Slightly more animated too.

This will require twice the number of counters (3->6) and switching from three 4-input AND gates to six 2-input AND gates. Shouldn't be that difficult to route on a two layer board (.... i hope)

Upgrade to 74HC series

These should perform better than the old CD4000 series. With better output drive, faster response and less quiescent current.

New Leds

The old 5mm sucked. So the new design will be built using small SMT leds. Likely standard 0805, though those may require a little extra indication to be correctly seen as a specific value.

Bring in the OR gates

To keep any output from going against another output, Proper OR gates will be used. Could have used Diodes, but this is more apt for the 4000 series theme of the project.

Schmitt triggered

All mechanical inputs, be they switch or button will get proper debouncing via a RC filter with a Inverting Schmitt Trigger and by default be pulled-up. This should eliminate any and all bouncing.

USB Powered

In this day and age USB is used for powering nearly everything. This project being 5V and even the original using very little power (~40mA). It should be viable to power this from even a standard 500mA USB port. May add a single header for a Battery pack.

Connector wise i'm going to us the purpose built Power-Only USB-C. Makes the most sense and i got myself a bunch of these USB4125 for stuff like this. They are cheap and so easy to solder. Never going back to Micro/Mini for power again!

Backup/Rechargeable Battery/Cap?

I liked my old clock having some persistance on data, being able to hold enough charge to keep going for about half a minute as i swapped thanks to the dinky supercap. BUT i should be able to do better than that. Which i will have to read into. Worst case scenario: The clock will be purely USB powered.

PCB and Casing:

The original was just a perf-board put inside a small picture frame. The new one will still be in a frame, albeit one purposefully 3D-Printed for it. Naturally I'll be going for a PCB design.

The PCB i hope to get done on a black board with a transparant mask on which the copper is still visible. Like the OSH After Dark type. This does mean avoiding ground pour on the front to keep contrast. Should make for an interesting look that fits well with the Frame Housing.