Have you ever wanted to connect a simple button or sensor to Home Assistant using Circuit Python? This script demonstrates registering a device with Home Assistant so that it can be automatically connected to an Automation. The script triggers its event on power-on. The example uses the "trigger" type, which is better than "button" for a simple remote control. Other MQTT integrations could put a sensor reading on the dashboard, or turn your CircuitPython board into a WiFi light or fan.

Ingredients

• ESP32-C3 board running CircuitPython 9.1.4
• Home Assistant with the MQTT integration and broker, accessible to the local network

This script also demonstrates setting a BSSID, a 12-digit hexadecimal string, to connect to a specific access point.

I was not able to connect to my local mosquitto MQTT broker over ssl; something about how the the MQTT client and broker interact prevents CircuitPython from validating the certificate. The comments include an example of loading a custom root certificate for the connection.

How It Works

Home Assistant's MQTT integration listens on the homeassistant/device_automation/# topic for discovery messages. When it sees a properly formatted message, it adds or updates that device under Settings > Devices and Services > MQTT > devices. It also listens on topic, here circuitpy/{unique_id}/action, for commands from the device. For a two-way device, you can also set a topic for Home Assistant to send commands back to CircuitPython.

Now, we can add our device to an automation in Home Assistant without any additional configuration.

Going Further

Can we send our configuration messages with mqtt_client.publish(topic, msg, retain=True) so Home Assistant will remember us, even if it restarts before we do?

Can we configure our CircuitPython board as a Home Assistant temperature sensor?

Can we put the device in low power mode, wake on a pin change, and make a real battery-operated remote control?

Use nginx to proxy SSL instead of mosqitto's idiosyncratic support.

See also