The Pi Clock is based on a Raspberry Pi Zero running a Waveshare e-ink display and using as little energy as possible to do it.
In addition to the time, it also shows sensor data like outside temperature, inside temperature. Current PV electricity production, as well as total electricity grid feed-in and usage.
The development kit includes examples written in Python, so I was able to quickly write up a script that could read the data and output it to the e-ink display. The drawing features of the PIL library were limited but sufficient enough to create a nice looking output.
It pulls its data via Wifi from my central server and is connected to a USB power supply for continuous power. It could also run off of a battery, but from what I found in my research online, it would have to recharge every 1-2 days and that would have been way too annoying.
It does take roughly 30s for the script to run an update until the display starts refreshing (which takes an additional 5 seconds).
Waveshare EPD 5in83 V1
Size: 5.83"
Resolution: 600 x 448
Colors: 2 (black / white)
Refresh time: 5s
Refresh interval: 180s min.
I really like using e-ink displays, but a clock is not the perfect use case, as it requires regular updates. Therefore there a some things to be aware of:
Pros
- Uses little power.
- Doesn't require back light.
- Price is ok for its size and resolution.
Cons
- This display should not update more frequently than every 3 minutes.
- This display doesn't support partial updates.
- Resolution isn't ideal for round elements, but it works.
There's been an updated version (V2) in the mean time, which increases the resolution to 648 x 480, but is otherwise compatible with the SPI interface.
In true prototype fashion the clock case was built with Lego - but since I got a 3D printer now, a custom printed case could also happen at some point.