A Rust async firmware for ESP32-C3 for reading and displaying sensor values using Embassy
https://gitlab.com/claudiomattera/esp32c3-embassy
The firmware runs on a ESP32-C3 microcontroller, samples environment data (temperature, humidity, pressure) from a BME280 sensor over I²C, and displays the latest sample on a WaveShare 1.54 inches model B version 2 E-INK display over SPI.
In particular:
- It uses Embassy as a general framework, and makes everything async, including communicating with sensor and display over I²C and SPI with
embedded-hal-async. - It is implemented on bare metal with
no_std, but withalloc(it is required for WiFi). - It is up-to-date with the latest crate versions (as of 2024-12-22).
- It uses
reqwlessfor HTTP requests and TLS.
It is mostly meant as a reference / example / starting point. The Rust + ESP32 + Embassy ecosystem is still very young, and I had a hard time putting everything together to make a complete application. Hopefully this project will be useful to other beginners :)
The firmware uses Embassy.
It starts by loading the current time from RTC Fast memory. If it is zero (as Unix timestamp), it means the clock has not been synchronized yet. So it connects to the WiFi network, and by making an HTTPS request to WorldTimeAPI to get the current time and time offset. This might be changed to use SNTP in the future, though that does not provide information about the time offset. Then it disconnects from the WiFi network (this is required to be able to enter deep sleep later).
After that, it creates structures for asynchronous I²C and SPI buses, a channel, and spawns two tasks with Embassy.
One task creates an interface the the BME280 sensor, then periodically reads a sample from it, and sends it through the channel. The other task creates an interface to the WaveShare E-INK display, then listens to the channel. Whenever a new sample arrives, it prints it on the display.
Meanwhile, the main task is sleeping for a longish amount of time. After that, it saves the current time (plus the expected sleep duration) to RTC Fast memory, and it puts the module to deep sleep.
The next time the module boots, it starts from the beginning. The clock will be initialized from RTC Fast memory, so the module will not connect to WiFi.
The architecture is more complex than it could be. There is no actual reason for spawning tasks and using channels to communicate with them. Or perhaps there is no actual reason for using the RTC Fast memory and deep sleep. Or even for using asynchronous I²C and SPI interface. And definitely there is no actual reason for using a TLS layer and connecting over HTTPS rather than HTTP. However, as mentioned earlier, this application is meant as a reference / example / starting point for more complex projects.
The sensor and the display must be connected to the correct PINs on the ESP32-C3 module.
For I²C (sensor):
- SDA -> GPIO1
- SCL -> GPIO2
- VIN/VCC -> 3.3v
- GND -> GND
For SPI (display:)
- SCK/SCLK/CLK -> GPIO6
- DIN -> GPIO7 (MOSI)
- CS -> GPIO8
- BUSY -> GPIO9
- RST -> GPIO10
- DC -> GPIO19
- VIN/VCC -> 3.3v
- GND -> GND
To get a development shell with the correct rust tooling, run:
nix developTo simplify your nix workflow, you can use direnv
echo "use flake" > .envrc
direnv allowThen either build as you would normally, with just and cargo:
just buildAlternatively you can build with nix:
nix buildSee the Changelog for a list of changes.
See the Contributing Guide for more information about development.
Copyright Claudio Mattera 2024
You are free to copy, modify, and distribute this firmware with attribution under the terms of the MPL 2.0 license (LICENSE-MPL-2.0.md or https://opensource.org/licenses/MPL-2.0).
You are free to copy, modify, and distribute this driver with attribution under the terms of either
- Apache License, Version 2.0
(file
LICENSE-APACHE-2.0.txtor https://opensource.org/licenses/Apache-2.0) - MIT license
(file
LICENSE-MIT.txtor https://opensource.org/licenses/MIT)
at your option.