bin-unicorn

Embedded application that interfaces with the Reading Borough Council API to fetch information about the next scheduled bin collection and display it. Targets the Raspberry Pi Pico W (RP2040) and runs on bare metal.

The app lights up LEDs corresponding to the next bin collection, as well as status LEDs. Collections will only be displayed if they are occurring on the current date or the next day; the device is intended to be more of a notification system than a calendar.

Once the app has successfully retrieved data on startup, it will poll the API every three hours to detect changes in data.

Hardware

I used 5mm LEDs and wired them up to the GPIO pins with a 330 Ohm resistor in-between.

GPIO pins

The following Pico GPIO pins are used by the software:

Pin	LED	Colour	Purpose
GP10	Diffused blue	Blue	WiFi connected indicator
GP11	Diffused red	Red	Error indicator
GP18	Blue	Blue	Food waste bin
GP19	White	White	Domestic (general) waste
GP20	Green	Green	Garden waste
GP21	Red	Red	Recycling bin

The colour is solely dependent on the LEDs you use and you can choose any colours you like.

Example setup

Here is how I wired it up on my breadboard - you can of course use more than one ground pin if need be.

An editable version of this diagram can be found at: https://wokwi.com/projects/461313005327349761

Development setup

The recommended workflow is to use Visual Studio Code with the Raspberry Pi Pico extension, which will handle installing the right version of the SDK and GCC ARM embedded toolchain.

If using a different setup or the command line, you need to install the SDK and toolchain manually, then set $PICO_SDK_PATH to the SDK path, and add the embedded toolchain's bin/ folder to your $PATH.

Per-user build values (WiFi credentials, project-specific secrets like BIN_UNICORN_HOME_ADDRESS) are sourced from environment variables.

Configuring per-user build values in VS Code

Open Preferences: Open User Settings (JSON) from the command palette and add:

"cmake.configureEnvironment": {
    "BIN_UNICORN_WIFI_SSID": "Your Network",
    "BIN_UNICORN_WIFI_PASSWORD": "Your Password",
    "BIN_UNICORN_HOME_ADDRESS": "40 Caversham Road Reading, RG17EB"
}

Notes:

• This goes in user settings, not the committed .vscode/settings.json.
• After editing user settings, pick the Debug preset in the CMake Tools status bar and reconfigure.

Building

Builds are done with CMake. On the command line you can run:

cmake --preset default
cmake --build --preset debug

This will produce an .elf file at build/Debug/bin_unicorn.elf and a .uf2 file at build/bin_unicorn.uf2.

You can build in VS Code by using the CMake Tools extension - select your build preset using the interface on the left, and then use the CMake: Build command to build (default shortcut: F7).

Deploying to Pico

In VS Code the Pico extension allows you to directly flash and debug onto a Pico connected via the debug probe using the menu options on the left: Debug Project and Flash Project (SWD).

If you don't have a debug probe, you can hook the Pico up directly to your PC and press the BOOTSEL button for a while until it shows up as a USB device on your system. Then either use the Run Project (USB) option from the extension or manually copy build/bin_unicorn.uf2 to the storage device.

It is advisable if you are deploying a finalised build to use a release build:

cmake --build --preset release

This will make the code much faster - for example, HTTP requests take 1 second instead of 5 seconds.

Porting

If you want to port this software to another microcontroller (like an ESP32), you are more than welcome to try! It should not be too difficult and I have made some effort to contain the usages of Pico-specific functionality to certain .cpp files. Most of the higher-level logic for interacting with the API and parsing the result is platform-agnostic.

Pico-specific files will have a preprocessor directive in them and will fail to build when not targeting the Pico:

#ifndef RASPBERRYPI_PICO2_W
#error This source file can only be compiled for a Raspberry Pi Pico 2 W.
#endif

Roadmap

This app is mostly complete, but some nice-to-have features would be:

• Expose a configuration interface so that the presently compile-time settings for the WiFI SSID and password, as well as home address, can be changed after the software is flashed.
• Allow over-the-air updates of the software in case it needs to be patched.
• Instead of sleeping for 3 hours after each successful request, use the date of the next collection to set a wake-up time further in the future. Could reduce power usage and enable the device to be battery-powered instead of needing to be plugged in.