Introduction: Electricity Carbon Intensity Display Using Pi Pico W and SSD1306

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This article shows how to use the new Raspberry Pi Pico W to download Carbon Intensity data using MicroPython over Wi-Fi and display it on a small OLED screen.

The Carbon IntensityAPI gives access to real-time data on carbon intensity and the generator mix producing electricity for the UK. It also provides a 96 hour forecast based on a machine learning (ML) model. This, coupled with reference data, produces current and future values for the carbon dioxide emitted per kilowatt-hour allowing consumers and smart devices to schedule electricity use to minimise carbon dioxide emissions.

The Pi Pico W is a new version of the Pi Pico board with the addition of a Cypress/Infineon CYW43439 chip making it more suitable for Internet of Things (IoT) applications. MicroPython currently supports the (2.4GHz) Wi-Fi functionality but not Bluetooth. CircuitPython doesn't support either, but Wi-Fi is planned.

The Cytron Maker Pi Pico Base is a board designed for beginners using the Pi Pico or Pi Pico W. The Maker Pi Pico Base is a variant of the Maker Pi Pico replacing the permanently-attached Pi Pico with female headers allowing any Pico with pins to be inserted. These boards have headers and blue LEDs for all of the GPIO, a small speaker, 3.5mm stereo output, a micro SD card slot, a reset button, three buttons, one RGB LED, a socket for an ESP-01 and six 3.3V Seeed Studio Grove connectors. Advanced users may find the board's headers and Grove connectors useful for rapid prototyping and experimentation.

The hardware implementation shown in this article uses approximately 150mW. The data only changes every 30 minutes making this a very suitable project for an electronic paper (e-ink) display. A permanent implementation would be more efficient on devices like an Adafruit MagTag or the new Pimoroni Inky Frame. These would make battery power a more practical prospect.

The carbon intensity data is also available on some tablet/smartphone apps and is likely to be eventually incorporated into domestic in-home displays for energy smart meters.

This project requires some simple, header soldering unless you purchase an SSD1306 screen and Pi Pico W with pre-soldered headers.

Supplies

Step 1: Step 1: Connecting SSD1306 Screen

The i2c-based screen (SSD1306) connects to the Maker Pi Pico Base's GROVE 1 connector:

  • SCL - GP0 (white),
  • SDA - GP1 (yellow),
  • VCC - 3V3 (red),
  • GND - GND (black).

The order of pins on the screen is not standard and may vary from the one in photographs. These screens appear to have onboard 10k pull-up resistors for the i2c bus lines which is likely to be sufficient. The GP0 and GP1 blue LEDs should both illuminate if the i2c bus is healthy - an idle i2c bus has both lines high. Data transfers will show up as small fluctuations in brightness.

Step 2: Installing MicroPython and Carbon Intensity Fuel Mix Program

If you are not familiar with MicroPython then it's worth taking a look at the (free to download) book: Get Started with MicroPython on Raspberry Pi Pico.

  1. Install the Thonny editor.
  2. Install the latest version of MicroPython with urequests for Pi Pico W. The Maker Pi Pico Base makes this a little easier as the board can be put in boot mode without yanking the USB power. Holding down the BOOTSEL button on the Pico and tapping the RUN button on the Maker Pi Pico Base will restart the board and make the RPI-RP2 drive appear.
  3. Setup Thonny for the Pi Pico W.
  4. Under Tools > Options... menu there is an interpreter tab where MicroPython (Raspberry Pi Pico) needs to be selected. Thonny doesn't distinguish between Pi Pico and Pi Pico W.
  5. Ensure Thonny can connect to the MicroPython interpreter on the Pi Pico W. Clicking on the STOP icon should show the interpreter's REPL mode in the Shell at the bottom.
  6. Download the files from GitHub:
  7. Click on the Raw button on ssd1306.py and use Save as in the browser to download the file to your computer.
  8. Click on the Raw button on carbon-intensity.py and use Save as in the browser to download the file to your computer.
  9. Create the secrets.py file (see example below) and fill in the values for your Wi-Fi.
  10. Load the three python files into Thonny and use Save as to save each one to the Raspberry Pi Pico - the carbon-intensity.py file can be renamed to main.py as part of the Save as operation to make it run when the Pico is turned on. The screenshots above show this selection box and the three files after they have been saved to the Pi Pico.
  11. On the tab now titled main.py, press the green start icon in Thonny to start the program.
# This file is where you keep secret settings, passwords, and tokens!
# If you put them in the code you risk committing that info or sharing it

secrets = {
  "ssid"         : "INSERT-WIFI-NAME-HERE",
  "password"     : "INSERT-WIFI-PASSWORD-HERE",
}

The Raspberry Pi Foundation's Connecting to the Internet with Raspberry Pi Pico W - Getting Raspberry Pi Pico W online with C/C++ or MicroPython may also be useful.

The MicroPython interpreter runs the main.py file at start-up. CircuitPython can confuse here as it also looks for code.py.

The versions used for this project were:

  • MicroPython v1.19.1 for Pi Pico W (with urequests and upip).

Step 3: The Displayed Fuel Mix Data

The SSD1306 screens are typically 128x64 pixels. MicroPython has an 8x8 font which allows 16x8 characters to be displayed.

The v1.0 version of the program in the photographs is displaying (from the top):

  1. The end time for the period the data covers in GMT/UTC/Zulu time. It would be useful to reformat this and localise it.
  2. A horizontal stacked chart summarising the fuel mixes for the generators. The blank section of the left represents green fuel sources with a carbon intensity below 150 gCO2/kWh. Nuclear fission is shown next with a thin filled bar. The solid bar on the right is for brown sources above 150. The reference values are currently stored in the code. The value per generator may vary for many reasons with imports/exports further complicating things!
  3. The two column table is the individual fuel type (truncated to four characters) and the percentage. The column split is based on the same carbon intensity threshold. The photo above shows the values at 6pm BST (17:00 GMT) on a sunny day in summer - solar is 14%. The photo at the start of the article shows 9pm values where, as expected, solar has dropped to 1%.

In v1.1 (shown on first page of article) the current (actual) carbon intensity value together with forecasted value are shown at the bottom of the display.

Step 4: Going Further

When you've got your carbon intensity display running, here's some areas to explore:

Related Projects:

Further Reading: