CCS811/BME280 on Raspberry PI 4

This document is to read sensor value of CCS811 and BME280 connected by I2C.
日本語はこっち。

• CCS811: ultra-low power digital gas sensor
  outputs: The equivalent CO2 (eCO2) and The Total Volatile Organic Compound (TVOC)
• BME280: Combined humidity and pressure sensor
  outputs: humidity and pressure and temprature

if you have API-key of OpenWeatherMap, this application can plot the forecast data. And if you live in japan, this application can plot historical data from the Japan Meteorological Associate.

Check I2C connection

Install i2c-tools, and check the connection.
CCS811 is address 0x5B (default), BME280 is address 0x77 (default).

$ sudo apt install i2c-tools
$ ls /dev/i2c*
/dev/i2c-1
$ sudo 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: -- -- -- -- -- -- -- -- -- -- -- 5b -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- 77

You can check hardware ID by script bellow.
The connection is OK, if hardware ID is correct.

#!/bin/bash

CCS811="0x5b"
BME280="0x77"
I2C_BUS="1"

# CCS811
# https://cdn.sparkfun.com/assets/learn_tutorials/1/4/3/CCS811_Datasheet-DS000459.pdf

ccs811_hw_id=$(i2cget -y ${I2C_BUS} ${CCS811} 0x20)
ccs811_hw_version=$(i2cget -y ${I2C_BUS} ${CCS811} 0x21)
# ccs811_fw_boot_version=$(i2cget -y ${I2C_BUS} ${CCS811} 0x23 w)
# ccs811_fw_app_version=$(i2cget -y ${I2C_BUS} ${CCS811} 0x24 w)

echo "CCS811 HW_ID: ${ccs811_hw_id} HW Version ${ccs811_hw_version}"
# echo "FW Boot Version ${ccs811_fw_boot_version}"
# echo "FW app  Version ${ccs811_fw_app_version}"

# BME280
# https://cdn.sparkfun.com/assets/learn_tutorials/4/1/9/BST-BME280_DS001-10.pdf

bme280_hw_id=$(i2cget -y ${I2C_BUS} ${BME280} 0xd0)
echo "BME280 HW_ID: ${bme280_hw_id}"

Read the sensor values

I2C devices such as /dev/i2c-1 do not need permission if you belong in i2c groupe. So add yourself to the i2c groupe. (Because I don't want to sudo every time.)

sudo usermod -aG i2c $USER

And Install smbus2 package that is required by python program to communicate by i2c.

pip install smbus2

Use this repository's code and read the values.

• Import these codes
  • bme280.py
  • ccs811.py

from bme280 import BME280

bme280 = BME280()
p, t, h = bme280.get()
print(f"{p:7.2f} hPa, {t:6.2f} C, {h:5.2f} %")

from ccs811 import CCS811

ccs811 = CCS811()
ccs811.compensate(h, t) # if needed
voc, co2 = ccs811.get() # May need to exec several times to get correct values
print(f"TVOC:{voc:4d} ppb, eCO2:{co2:4d} ppm")

Example

Command Line

See example.py. This example outputs to stdout every 1 second.

#!/usr/bin/env python

from time import sleep
from bme280 import BME280
from ccs811 import CCS811

ccs811 = CCS811()
bme280 = BME280()
p, t, h = bme280.get()
ccs811.compensate(h, t)

while(True):
    try:
        p, t, h = bme280.get()
        voc, co2 = ccs811.get()
        print(f"{p:7.2f} hPa, {t:6.2f} C, {h:5.2f} %, TVOC:{voc:4d} ppb, eCO2:{co2:4d} ppm")
        sleep(1)
    except OSError:
        # i2c bus somtimes cannot access
        continue
    except KeyboardInterrupt:
        break

GUI (matplotlib)

See example_gui.py. This example updates the graph every 0.2 seconds.

• Require: pip install matplotlib numpy

GUI (dash)

See save_csv.py and dash_from_csv.py. This example is updates the csv file every 10 minutes, and provides Web view that read from the file by dash framework.

• Require: pip install dash pandas numpy lxml
• Note:
  • Temperature offset: Decreased 2 Celsius degree, because the board has self-heating.
  • Time-zone: Hard-coded in Asia/Tokyo (UTC -9 hours)

If you have OpenWeather Map API key, API key set as bellow and can display weather forecast data.

echo "API_key = {API key}" > ./openweathermap/api_key.py