BME680 gas and weather sensor

The Bosch BME680 reads temperature, humidity, pressure and the resistance of a heated gas plate, over I2C at 0x77 or 0x76.

Aliases: BME688, BME68x, Adafruit BME680, GY-BME680, air quality sensor. It is a BME280 with a tiny hot plate added: volatile compounds in the air lower the plate's resistance, so a falling gas reading means worse air.

Pins

Pin	What it does
VIN	Supply, 3 to 5 V on the board.
GND	Ground.
SCL, SDA	I2C. The board carries the pull-ups.

Properties

address is 0x77 or 0x76. temperature, humidity, pressure (hPa) and gas (kilohms) are the air; the four sliders change them while the circuit runs.

Reading it on an Arduino

With Adafruit's library, which Mokxi ships as Adafruit_BME680.h:

#include <Wire.h>
#include <Adafruit_BME680.h>
Adafruit_BME680 bme;

void setup() {
  Serial.begin(9600);
  if (!bme.begin()) Serial.println("No BME680");
  bme.setTemperatureOversampling(BME680_OS_8X);
  bme.setGasHeater(320, 150);   // 320 C for 150 ms
}

void loop() {
  if (bme.performReading()) {
    Serial.print(bme.temperature);
    Serial.print(" C  ");
    Serial.print(bme.gas_resistance / 1000.0);
    Serial.println(" kohm");
  }
  delay(2000);
}

Bosch's own bme68xLibrary.h (the Bme68x class) reads the same part.

How it talks

• Power on and the soft reset (0xB6 to 0xE0) take 2 ms. chip_id (0xD0) reads 0x61.
• Writing forced mode to ctrl_meas (0x74) runs one cycle: temperature, pressure and humidity at their oversampling, then with run_gas set the heater step held for its wait and the gas reading. measuring in 0x1D reads 1 until it ends, then new_data_0 is set and the mode goes back to sleep.
• The results are raw counts at 0x1F to 0x2B. The library turns them into the weather with the calibration words at 0x8A to 0xA0 and 0xE1 to 0xF0, so the arithmetic is the library's own.

What it does not model

The IIR filter, the heater's real temperature, and the gas resistance's dependence on it and on humidity: the gas reading is the slider's resistance.

Common mistakes

Expecting a gas reading the moment the sketch starts: the heater has to run for the wait the sketch sets, and the reading comes at the end of the cycle. Comparing gas readings across boards: the figure only means something against the same sensor's baseline.