Outline

This project is intended to be a low power clock, suitable to use as a travel clock, and also suitable as a room clock.

This unit uses an E-Paper display, along with an RPi2040 processor, and is powered by a LiPo battery. An on-board battery charger is present, this charges the battery using a USB power source.

The processor only updates the display once per minute, and hibernates between updates to maximise the battery life.

The unit updates it’s time once a day from the internet.

A diagnostic mode / interface is also built-in, this allows a pair of Wi-Fi access Point SSID/Passwords to be entered/stored.

To build this unit in the slim case (portable drive case), I had to cut the RP2040 connector off the back of the board.

Todo: show complete unit in its case.

Todo: show RP2040 connector off the back of the board.

Design Notes

• 1 The RP2040 USB connector can power the unit, it’s also used to program the RP2040.
• 2 The TP4056 board USB is for charging the LiPo battery.
• 3 The externally available USB is for day to day running of the clock from an external power source.

The software libraries for the E-Paper display require the Raspberry Pi SDK and its associated development environment, I had a lot of trouble getting on with this, and it curtailed my development of the item.

Special Font(s) had to be created for the display.

Todo: show Schematic

Images

PCB

Build Notes

Operation Notes

Development / Prototyping

This project was difficult to implement, primarily because of the RPi development framework being imature, and me not wanting to learn it just for this one project. Also this was prior to RP introducing the debug probe, which would have helped.

It was also difficult mechanically to design an build, it took a lot of time.

At least two itterations of PCBs were required.

Applicable Links

Waveshare 3.7inch E-Paper E-Ink Display Module for Raspberry Pi Pico, Black/White, 480×280 Pixels

2

Fontedit

I spent a lot of time generating some large Text Font characters for the display, and a celcius symbol. I have forgotten how I did this, but I know I used some third party open source tools.

Make a new larger font for Waveshare SPI

A desktop app to import, edit and export fonts as byte arrays for use in embedded systems fontedit font2bytes

Todo: show case kit sites