This firmware, written in Rust using embassy-rs, is designed for the Raspberry Pi Pico 2 W platform using the RP2350 microcontroller. Its application is an environment-sensing device which can measure CO₂ concentration in the atmosphere, ambient temperature and humidity.

The effects of increased CO₂ concentration on cognitive function become increasingly pronounced at CO₂ concentrations exceeding 1000 ppm. There's a fantastic YouTube video by Kurtis Baute and Tom Scott which you can watch for a short summary. Open your window right now!

Building

Prerequisites

Rust compiler & cargo package manager: https://www.rust-lang.org/
probe-rs for programming the device, receiving RTT logging output & debugging
ARM bare metal compiler toolchain
- arm-none-eabi-gcc (& arm-none-eabi-newlib) on Arch Linux, your system may have different package names
The ARMv8 or RISC-V Rust toolchain:
- ARMv8: rustup target add thumbv8m.main-none-eabihf
- RISC-V: rustup target add riscv32imac-unknown-none-elf

Notes

This project's Cargo.toml includes a custom build profile ("dist") which optimises the executable for maximum performance at the cost of slower build times. This profile is designed for flashing a final build onto an end user's device.

By install probe-rs as mentioned in the prerequisities you will have access to cargo flash and cargo embed for flashing the executable onto the device.

Compiling & running

cargo build (or cargo build --release / cargo build --profile dist)

If you wish to run the binary on your Pico (connected in BOOTSEL mode):

cargo run (or cargo run --release / cargo run --profile dist)

Hacking & debugging

This project uses probe-rs for flashing & debugging, though one may use picotool and OpenOCD instead if you so wish. Ensure that you have a debug probe which supports to RP235x series of chips and supports the SWD protocol. I use the Raspberry Pi debug probe (USB VID:PID 2e8a:000c) for debugging the device using the on-board debugging pins.

TODO / Future improvements

Companion smartphone app using BLE to receive measurement data from the device for notifications & further analysis/tracking
Low-power state, reducing screen brightness, sensor sampling rate and putting periphals to sleep
3D printed case housing the MCU, sensor, display and rechargable lithium ion battery