bme680

A custom HomeKit accessory with Python

/ Denis / Leave a comment

Hi 👋,

In this short article I want to showcase how I implemented a custom HomeKit accessory with python.

My Home Assistant’s SD card died ðŸŠĶ a few days ago and the support for GPIO based sensors will be removed in newer releases. This makes it unsuitable for my needs, while giving me the perfect opportunity to try other things.

To continue monitoring temperature and humidity in my home I’ve built a custom HomeKit accessory with HAP Python.

The Sensor

A BME680 air quality sensor is used to monitor temperature and humidity. It is connected to the PI according to the following diagram:

The communication with the Pi is done using the I2C protocol. If you want to use I2C in your own setup, it has to be enabled using raspi-config, as it doesn’t come enabled by default.

# Execute
sudo raspi-config
# Then select Interfacing options->I2C and enable it.

Connection can be tested with the following command:

sudo apt-get install build-essential libi2c-dev i2c-tools python-dev libffi-dev git
/usr/sbin/i2cdetect -y 1

pi@raspberrypi:~ $ i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- 76 --

It will output the address that the sensor is using, in our case the 0x76 I2C address.

The Code for the Accessory

You can browse the full code for the accessory and bme680 sensor in my git repo.

To run the program, clone the repository and ensure that you’re running it under the pi user, otherwise you will need to change some things.

cd /home/pi && git clone git@github.com:dnutiu/bme680-homekit.git && cd bme680-homekit
sudo apt-get install libavahi-compat-libdnssd-dev
pip3 install -r requirements.txt

Verify that the program works by running python3 main.py. Running it the first time will prompt you to add the accessory to the Home app. If you miss this step you can repeat it by deleting the accessory.state file located in pi’s home directory and by running the program again.

After you’ve verified that it works, you can setup a systemd service to run the accessory’s python script when the PI boots

Copy the bme680-homekit.service to /etc/systemd/system and check that the service is running.

sudo cp bme680-homekit.service /etc/systemd/system
sudo systemctl status bme680-homekit

If you want to run this under another user rather than the pi, you’ll need to tweak the bme680-homekit.service file.

Congratulations for making it this far! 🎉

You can browse more code examples in the HAP-Python repository.

Thanks for reading and have fun! ðŸ‘Đ‍ðŸ’ŧðŸ‘Ļ‍ðŸ’ŧ ⚙ïļ

BME680 Home Assistant Integration

/ Denis / 2 Comments

Hi 👋,

In this short article I will highlight how to use the BME680 Home Assistant integration with a BME680 Sensor.

Please note that I’m running Home Assistant core on Raspbian OS.

Raspberry Pi Setup

Before connecting the sensor, you will need to enable the I2C interface on your Raspberry Pi and install some additional tools that are useful for debugging.

To enable the I2C interface execute:

sudo raspi-config

Then go to Interfacing options->I2C and select yes.

Next, install the following packages:

sudo apt-get install build-essential libi2c-dev i2c-tools python-dev libffi-dev

Sensor Setup

The first step is to buy the sensor, get one with headers already soldered if you can otherwise, you’ll need to solder them.

I got mine from Pimoroni and I’ve never was disappointed by them, they deliver to EU.

BME680 sensor. Pimoroni screen capture 2022-01-16

Next depending on which headers you’ve chosen; you will need four male-to-female jumper wires to connect the BME680 to the Raspberry Pi.

To connect the sensor to the Raspberry PI, refer to the following diagram:

You will need to connect the wires to the following buses:

  • Sensor Power -> Raspberry PI 3.3V
  • Sensor GND -> Raspberry PI GND
  • Sensor SCL -> Raspberry PI SCL
  • Sensor SDA -> Raspberry PI SDA

Check that the sensor is detected using the following command on the Raspberry Pi.

/usr/sbin/i2cdetect -y 1

You should get an ouput like this:

0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- 3c -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- 76

The sensor’s I2C address can be 0x76 or 0x77. According to the above output, the sensor address in our case is 0x76, keep this in mind.

Home Assistant Setup

Add your homeassistant user to the I2C group by running:

sudo addgroup homeassistant i2c

Next, open configuration.yaml and modify the sensor and homeassistant.customize sections according to:

Don’t forget to replace i2c_address : 0x76 with your i2c address if it’s different.

homeassistant:
  name: HomeKit NucuLabs
  unit_system: metric
  time_zone: Europe/Bucharest
  customize:
    sensor.bme680_sensor_temperature:
      icon: mdi:thermometer
      friendly_name: Temperature
    sensor.bme680_sensor_humidity:
      icon: mdi:water
      friendly_name: Humidity
      device_class: humidity
      unit_of_measurement: "%"
    sensor.bme680_sensor_pressure:
      icon: mdi:gauge
      friendly_name: Pressure
    sensor.bme680_sensor_air_quality:
      icon: mdi:blur
      friendly_name: Air Quality
      device_class: pm25
      unit_of_measurement: "%"

sensor:
  - platform: bme680
    i2c_address: 0x76
    monitored_conditions:
      - temperature
      - humidity
      - pressure
      - gas
      - airquality

Reboot the device after you’ve modified configuration.yaml by running sudo reboot.

Note: The customize section sensor.bme680_sensor_air_quality sets the device class of BME680 air quality measurement to pm25, but this isn’t a pm25 measurement, it’s a proprietary algorithm according BME680 Datasheet. High values indicate good air quality while low values indicate low air quality. On the other hand, in pm25 measurements high values indicate bad air quality and low values good air quality.

This is a hack and it’s up to you if you want to keep it. If you don’t set the device class to pm25 then the measurement won’t be visible in Apple Homekit because Homekit is not aware of this kind of measurement. If you know any other way of making it visible in Homekit let me know. 😀

After home assistant reboots, the following entities should be available in the Lovelace UI:

Thanks for reading! ðŸŧ