Intro
Neither my wife or me wear watches: on the go, we mostly use our phones to look up the time, and at home there always used to be some convenient screen nearby. However, since we moved places, the living room lacks always-on screens indicating the time, and especially my wife doesn't always has her phone on her when we were at home. Knowing the time is kind-of important nowadays, and so one day she asked me if we could get a clock for the living room.
Obviously, I wasn't going to buy an off-the-shelf clock. Clocks are fairly simple devices, with only one function: to tell the time. However, there are a lot of technologies available to do this: from a classic old-school mechanical clock to a marble clock to various electronical ways of displaying 'digital' digits on LCDs and other displays. And that is when you're limited to showing time the ordinary way: there are als odd creatures like the binary clock or the Mengenlehreuhr in Berlin. It's a really nice engineering challenge to create one that is optimized to what you need in a particular case, or alternatively let your creativity roam free to make one out of unconventional components. It's an opportunity for a cool project that I'd rather not let go to waste.
In this particular case, I had a list of things that I wanted the clock needed to do:
- Battery-driven. We wanted to put it on a glass wall, meaning any wire to a power adapter would be visible.
- Readable during the day and in low light. Our living room gets a lot of sun during the day, so being able to read the time at a glance in bright sunlight was important.
- Large enough, again so it's readable from a distance at a glance. We also want to know the time in the evening, and high contrast would be useful then.
- Low-maintenance. I don't want to have to set the time, and the batteries should last a long time between charges.
- Interesting. If I'm gonna make something, I'd at least have some people go 'huh' when they watch it. I also wanted it to be interesting to build: it's no fun if there isn't at least a bit of a challenge.
Given these requirements, I immediately imagined that an E-ink display would be something that would work here. It is low-power, so I could run the clock from a battery for a long time. E-ink also has a high contrast, and I have enough experience running those things off an ESP32. Using an ESP32 type chip would also mean that I could get the time off the network, meaning the clock would always run on time.
An issue was that I wanted the clock to be pretty large, and big E-ink displays unfortunately also come with a pretty large price tag. Then I got an idea: why didn't I make four separate smaller 'clocks' instead? Every one could display a separate digit of the time, and by simply hanging the digits on the wall in the correct order, you'd have a larger clock.
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