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Log temperature from an MCP9808 sensor to Google Cloud with Google Cloud IoT Core
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README.md

MCP9808 Temperature Logger

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Log temperature from an MCP9808 sensor connected to a Raspberry Pi.

Send temperature to Google Cloud IoT Core, which can then be saved and plotted using the Google App Engine app in the web directory:

make

# Example device.json:
# {
#   "project_id": "my-gcp-project",
#   "registry_id": "my-iot-core-registry",
#   "device_id": "my-device",
#   "priv_key_path": "my-device.pem",
#   "region": "us-central1"
# }
./out/iotcorelogger -device device.json -cacerts roots.pem

Set up a cron job, use it in a daemon, the world's your oyster...as long as the world is temperature values read from the MCP9808.

Choose a Client

NOTE: The Python client is unmaintained! It may be deleted in the future. Please use the Go client.

This project includes clients — code that runs on the Raspberry Pi to read the temperature and log it — written in Go and Python.

Use the Go client if you're sending temperature data to Google Cloud IoT Core (it only supports Cloud IoT Core at the moment). It's easier to work with than the Python client because you get a statically-linked binary that just works on the Raspberry Pi. You don't have to clone this repository on the Raspberry Pi or install dependencies or set up a virtualenv. Just make and run.

Use the Python client if you want to log directly to Google Cloud Pub/Sub, or to Google Sheets. The Python client supports Cloud IoT Core as well. Note: This project only supports Python 3. The future is now. The future was in 2008. Come with us into the future.

Prerequisites

Each client's README has information about its prerequisites.

Regardless of your choice of client, you'll need to:

Setting up Google Cloud IoT Core logging

The scripts at https://github.com/mtraver/provisioning are useful for creating the CA key and cert and device-specific keys and certs described below.

  • Create an IoT Core registry. The IoT Core quickstart provides more info. The registry includes:
    • A Pub/Sub topic for telemetry (you'll need to create the topic if it doesn't already exist)
    • A Pub/Sub topic for state (you'll need to create the topic if it doesn't already exist)
    • A CA cert for verifying device certs. This can be self-signed.
  • Add devices to the registry. This requires a device-specific cert that chains to the CA cert. The key and cert can be made with the scripts in the repo linked above. Heed the information there about key handling and about the device ID (the device ID you use when making the cert must be the same as the one you set when adding the device to the registry).
  • Create a subscription to the registry's telemetry topic. Configure it to push to the /_ah/push-handlers/telemetry endpoint of the web app. This is how IoT Core is tied to the web app.

The end-to-end flow is like this:

  1. A device sends a payload (in this case a protobuf; see measurement.proto) to IoT Core.
  2. IoT Core publishes the payload as a Pub/Sub message to the registry's telemetry Pub/Sub topic.
  3. Pub/Sub pushes the message to the web app's endpoint, as configured in the subscription to the topic.
  4. The web app receives the request, decodes the payload, and writes it to the database.

Setting up Google Cloud Pub/Sub logging

TODO

Setting up Google Sheets logging

Google provide a guide to using the Sheets API in Python: https://developers.google.com/sheets/api/quickstart/python.

  1. Follow "Step 1: Turn on the Google Sheets API" and use the wizard linked there to make a project and set up access credentials. What you want is a "service account", which is what the wizard will recommend if you say that you want access from a headless device/crontab/etc. You'll get an email address that looks something like this:

    <something>@<something>.iam.gserviceaccount.com

    You'll also get a JSON file containing the key for that service account. Put it in a safe place.

  2. Now make a Google Sheets spreadsheet and share it with the service account email address, giving edit permissions.

    Note the spreadsheet ID. For the example URL below, the ID is 1BxiMVs0XRA5nFMdKvBdBZjgmUUqptlbs74OgvE2upms:

    https://docs.google.com/spreadsheets/d/1BxiMVs0XRA5nFMdKvBdBZjgmUUqptlbs74OgvE2upms/edit

The JSON key file and spreadsheet ID are the two things you'll need to log to the sheet.

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