MCP9808 Temperature Logger

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 web app in the web directory. Running make will build all binaries locally. Running make web-image will build a Docker image that can be deployed to Cloud Run to serve the web app.

Run the iotcorelogger binary on the Raspberry Pi:

make

# Example config.pb.json
# {
#   "supported_sensors": ["mcp9808"],
#
#   "jobs": [
#     {
#       "cronspec": "0 */2 * * * *",
#       "operation": "SENSE",
#       "sensors": ["mcp9808"]
#     }
#   ]
# }

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

The config file sets up the sensors and schedules jobs using cron syntax, and the device file specifies how to connect to IoT Core's MQTT broker to report telemetry.

Prerequisites

• Wire up the hardware. Adafruit have a nice tutorial: https://learn.adafruit.com/mcp9808-temperature-sensor-python-library/overview
• Enable I²C on your board. For Raspberry Pi, this can be done with raspi-config. You'll find the "I2C" option under either "Advanced Options" or "Interfacing Options".

Setting up Google Cloud IoT Core logging

Google Cloud setup

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 /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.

Client program

The program in cmd/iotcorelogger runs on the Raspberry Pi and sends data to Google Cloud IoT Core. cmd/README has information on building and configuring iotcorelogger.

TODO(mtraver) add info on systemd config

Running and deploying the web app

Environment variables

The web app expects the following environment variables to be set. Define them in a file called env and the make run-web command below will pick them up.

In production, you'll need to make sure that they are available to the container via env var config, secrets config, or whatever other method you like.

TODO(mtraver) add descriptions of the env vars

• PUBSUB_VERIFICATION_TOKEN
• PUBSUB_AUDIENCE
• INFLUXDB_SERVER
• INFLUXDB_TOKEN
• INFLUXDB_ORG
• INFLUXDB_BUCKET

For local development you'll need to set GOOGLE_CLOUD_PROJECT to your GCP project ID. In production on Cloud Run it's fetched automatically.

For local development you'll also want to put a key for a service account that allows reading from Google Cloud Datastore and Google Cloud IoT Core in a dir called keys and then set the GOOGLE_APPLICATION_CREDENTIALS env var, e.g.:

GOOGLE_APPLICATION_CREDENTIALS=/keys/my-key.json

In production GOOGLE_APPLICATION_CREDENTIALS isn't necessary because the service will have the proper permissions granted to it.

Build and run locally

Did you make your env file and put your service account key in keys? Do that first (see above).

PROJECT=my-gcp-project-id REPO=my-artifact-repository-repo-name make web-image
PROJECT=my-gcp-project-id REPO=my-artifact-repository-repo-name make run-web

Build on Google Cloud Build

This will build the image remotely and push it to Google Artifact Repository.

PROJECT=my-gcp-project-id REPO=my-artifact-repository-repo-name make web-image-remote

Deploying to Cloud Run

Deploy the image built with make web-image-remote to Cloud Run and make sure that the env vars (aside from GOOGLE_CLOUD_PROJECT and GOOGLE_APPLICATION_CREDENTIALS) are made available to it.