“I had a few of these 8x8 LED dot-matrix displays in the drawer and was thinking about what to do with them. Inspired by other instructables, I got the idea to build a count down/up display to count down to a future date/time and if the target time passed, count up from it. I made this now my retirement clock sitting on the shelf.
The idea to put it into a bottle was more of an accident while thinking about a casing. Others put ships into a bottle, why not a clock?
I also wanted to make the clock obey daylight saving time and of course remember the settings and time when being unplugged. I am powering the clock via USB which makes it reprogrammable if you’d like to do something different or just add features to the code. The code is pretty simple and could also use a lot of optimizing. I did not take good care about RAM consumption I have to admit. If I got the time and motivation, I’ll come back to it.
1. Arduino Nano
2. RTC (I used the common DS3231 which also has an EEPROM)
3. 12x 8x8 dot matrix module. (I had the quad modules which are easier to line up)
4. LDR to adjust the display brightness
5. Resistor 10 kOhm
6. Capacitor 5x 100 uF suppressing spikes from the display
7. To increase the contrast of the 8x8 modules, I used the dark tinted “Window Film”. The Display shows the LEDs as white dots if not lit. The window film turns it a shiny black look.”