Some years ago you could buy the "Tix Clock" for around $40US. This original one was described as
- Brushed metal faceplate
- Available in Silver or Black
- LED illuminators last indefinitely
- Three display update options (every second, every 4 seconds, every minute)
- Three dimming levels
- May be mounted horizontally or vertically
- May be placed on desk or wall mounted
- Runs on 6V AC with included (US) wall transformer. Auto-sensing. 50 or 60 Hz.
- Actual size 10.2″ x 3.0″ (x 1″ deep)
One thing you don't see is battery backup so when the power goes the time is lost. Note there the "AC" adapter. A little investigation shows that this clock use the A/C as timebase and that is one reason it is no battery backup.
The basic build is a simple 3x9 led matrix controlled by a PIC16F628. At first I was considering reprogramming the pic to read time from an RTC but it's only one free pin plus I suspect it might be tight on program memory. While I could possible repurpose the AC sensor pin and hook up a i2c RTC module to those two pins, replace the pic with some different model (for more memory) and possible get it talking I2C over those two pins it would be hard for me since I have no knowledge at all regarding PIC programming and it would also be the end of the road since it would be no way I could add a wifi connection to it or so.
Did think about options for a while and noted that the PIC is in a socket which means all required io and even power is easily available there. I decided to make a breakout board that will connect to the existing socket and then a small board on the side with an arduino nano, rtc module and possible also a wifi connection and maybe a radio receiver for correct time.
The code here is licensed under GPL3 and is what is put on the arduino nano. It is similar behavour to the original code but have some added features to handle the rtc.
Short demo at https://www.youtube.com/watch?v=QV_h11XrtCI