esp32c3-rust-mqtt

This will eventually be a little rust-based esp32 project for connecting up esp32 to mqtt, using nix as a build system. I'm hoping to have it build from aarch64-darwin as well as x86_64-linux. It will eventually be hooked into home-assistant.

Using nix adds some complexity but should help ensure reproducibility; my blog post detailing my process for getting a prior iteration working (prior to the release of esp-wifi on crates.io) may be useful to novices and hobbyists (such as myself): https://n8henrie.com/2023/09/compiling-rust-for-the-esp32-with-nix/

Security

This project takes the straightforward route of pulling sensitive values from environment variables and burning them into the microcontroller. This means that an attacker with physical access could almost certainly pull that information from the microcontroller or the build artifacts from compiling this project.

These values include but are not limited to:

• network SSID
• network password
• MQTT username
• MQTT password

Further, I have taken the lazy route of inheriting these environment values into the nix environment, and as such the nix store will have a world-readable copy of all these values. This could be mitigated to some degree by something like sops or agenix, but the final binary (also in the nix store) would still contain the values, so I don't think this effort is worthwhile at this time.

Quickstart

$ git clone https://github.com/n8henrie/esp32c3-rust-mqtt
$ cd esp32c3-rust-mqtt
$ cp .env{.sample,}
$ $EDITOR .env
$ . .env
$ cargo run --release

Alternatively, nix run --impure instead of cargo run --release.

Power Usage and Binary Size

Just out of interest, my ESP32C3 running this project uses about 0.075A @ 5.24V (single point in time), and its usage over time seems a little lower at 0.10Wh over 18 mins (~33W).

Update 20250809: With newer code, including a regular ping to ensure a persistent connection to the MQTT server, my ESP32C3 used 14.82 Wh over 47h32m (avg 0.31W); interactive usage was minimal and it was not regularly reporting any data over this interval (but I would occasionally toggle the LED on and off over the network to make sure everything was still connected). (This was connected directly to a USB power meter and therefore would not include any losses from an inverter.) The device gets quite hot.

Temperatures

• Baseline:
  • 5b4ba9c46d6839943196fded2faf1b9452af9dde
  • MCU (sensor): 192.1ºF
  • MCU (IR): 85ºF
  • antenna (IR): 87ºF
• PowerSaveMode::Maximum
  • ff780f3e82cc7de8a013276e5de4df7f147570ce
  • MCU (sensor): 189.7ºF
  • MCU (IR): 81ºF
  • antenna (IR): 87ºF
• CpuClock::_80MHz
  • c00f15a496f476bd4ce1d9cc83c45f2ab17fca82
  • MCU (sensor): 185.8ºF
  • MCU (IR): 84ºF
  • antenna (IR): 86ºF
• PowerSaveMode::Maximum && CpuClock::_80MHz: 97 ()
  • 7fffe96d7275a255362c21ebbaf22f28efab9f43
  • MCU (sensor): 186.6ºF
  • MCU (IR): 86ºF
  • antenna (IR): 88ºF

File size:

$ ls -l target/riscv32imc-unknown-none-elf/release/esp32c3-rust-mqtt
-rwxr-xr-x 1 n8henrie staff 8707804 Aug  9 08:48 target/riscv32imc-unknown-none-elf/release/esp32c3-rust-mqtt

TODO

• defmt doesn't like the variables in the println statements. Is it worth converting them?
• would a brief sleep in the hot loop meaningfully decrease the power usage?
  • adding 200 - 500 ms sleep brings power down only very slightly, to about 30W
• is there a way to have each receive and publish task by their own embassy_executor::task?
  • if so, is this desireable?

Related projects to keep an eye on

• https://github.com/bjoernQ/esp32-rust-nostd-temperature-logger
• https://github.com/mountainlizard/mountain-mqtt/
• https://github.com/siemtim-dev/embedded-mqttc
• https://github.com/11mad11/esp32
• https://github.com/bjoernQ/esp32-rust-nostd-temperature-logger