Use python smbus2 to I2C between Pi and I2C device

1. I2C

1.0 I2C Devices

• AHT10: measures humidity in % and temperature in Celcius. Not use anymore.
• AHT21: measures humidity in % and temperature in Celcius.
• CCS811(board name is CJMCU-811): measures equivalent CO2 in ppm and Total Volatile Organic Compound in ppb. Not use anymore.
  • Notice: nWAKE should be LOW
• BME680: measure temperature, humidity, pressure, air quarity.
• MCP9808: measure temperature
• SSD1306: 128x64 pixel OLED display

1.1 Install linux i2c tools

sudo apt install i2c-tools

then, try

i2cdetect -y 0


#### Trouble shooter

If there is error,

Error: Could not open file `/dev/i2c-3': Permission denied
Run as root?

add your user to i2c group,

sudo usermod -aG i2c your_username

and reboot.

1.2 Preperation

1.2.1 Install python3 pakages

Used python packages:

• pyi2c: to communicate with I2C devices. This includes smbus2
• influxdb_client: to save measurement data to InfluxDB server

Install python packages

pip install -r requirements.txt

or

pip3 install pyi2c influxdb_client

1.2.2 Get InfluxDB token

In shell, type this to add new environment variable.

export INFLUXDB_TOKEN=your_token_here

Or, create a script file, such as env.sh

#!/bin/bash
# env.sh

export INFLUXDB_TOKEN=your_token_here

and type in the shell

source env.sh

1.3 Run

python3 i2c.py

Run in background

nohup 2>&1 python3 i2c.py &
# nohup python3 i2c.py > logs/i2c.out &

1.4 Startup on boot

Edit /etc/rc.local and add below lines

# -----------------------------------------
# i2c
cd __current_directory_path__
sudo -u __username__ ./startup.sh
# -----------------------------------------

To check rc.local, run

sudo systemctl status rc-local

2. Data visualization by using InfluxDB

3. Webserver (Not use anymore)

3.1 Preperation

• django

pip3 install django

3.2 Run

./runserver.sh

For developers

Reset SQLite3 django model

python3 manage.py migrate --fake monitor zero
find . -path "*/migrations/*.py" -not -name "__init__.py" -delete
find . -path "*/migrations/*.pyc"  -delete
python3 manage.py makemigrations
python3 manage.py migrate --fake-initial

How to Reset Migrations

Datasheets

• AHT10
• CCS811 for v2.x.x
• CCS811 for v1.x.x

Reference

• CJMCU-811