The newer Echo Dots from Amazon have pretty neat clocks at the front, which can display not only the time but also timers, temperature, and more, but the older Alexas don't have such a display. However I like some of the older, "larger" Alexas, because of their sound quality, especially for the living room.
Now my situation is that i have some nice sounding Alexas in my living room, but no way of showing timers, that i set in my living room, let alone on the same device as i would normally see the time (like a clock).
The features that i wanted for my clock is to display the remaining time of a timer, as well of showing the current time, if no timer is set. I don't care about showing the weather or other stuff, as that would add a huge amount of hassle, as i want to work with simple 7-Segment displays.
The idea that came to my mind, how i could realize that, was to simply use one of those cheap 4 digit displays with some multiplexing, since the RA4M1 on the Uno R4 WiFi should be strong enough for that, right?
The display was WAY to flickery to look at, since the arduino had to do some other work (like catching mqtt often which acts like a delay).
The fix for that behaviour was to use another arduino (Uno R3) to do the multiplexing. So the Uno R4 WiFi would get the time from NTP and the remaining time on the timer of the Alexa (via mqtt/ioBroker) and send those numbers over UART to the Uno R3, which then displays it without ANY flickering!
Now i had what i wanted, an digital clock, which displays the time, unless a timer was set on the living room Alexa. Great! But it didn't look great, as there were two arduino Unos and an ugly looking breadboard with those tiny 7-Segment displays on top of my cupboard.
The next step was to get rid of the Uno R3 and get some bigger displays.
This was a rather simple step. I had some 74HC595 and five meters of some cuttable 12V RGB COB LED-Strip Laying around waiting for some project.
Now i just had to convert the code of the Uno R4 WiFi from giving out the time via UART to using shiftOut()
Since the LED-Strip is cuttable about every 3,3cm and we know, that we will need 4 times 7 Segments, its pretty easy to calculate, how big our Segments will get:
5m / (4 digits * 7 segments) = 17,86cm
which we have to make devisible by 3,3cm:
17,86cm / 3,3cm ≈ 5,4 cuttables
which means, every segment will be 5 cuttables long, which means every segment has a length of 16,5cm.
So in conclusion the whole clock display will be about 33cm high which should be enough to be readable from across the room!