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    BME680: Gas sensor heater unstable

    BME680: Gas sensor heater unstable


    Dear members,  I am evaluating the BME680 for smoldering fire detection in a dirty environment, which means that I am looking for a way to discriminate easily and heavily oxidizable gas species. For that purpose, I have forked from Bosch's BME680 driver to make use of the sensor's ability to configure and query 10 different heater configurations (temperature and duration). You can find the modified code here: 

    I use all possible ten heater configurations; each step has a duration of 50 ms. That is more then the 20-30 ms which, according to the documentation, are required to achieve a stable heater temperature. The temperatures are 400°C down to 130°C in decrements of 30 K.

    Here comes my problem: Normally, that configuration works fine. I have tested it with a BME680 on a Joy-It breakout board connected directly to a Raspi 3 via I²C at 3.3 V, and it runs flawlessly for days. I have recorded a communication cycle with an oscilloscope; see Scope_regular.png

    In my lab setup driven by a Odroid C2, however, there are three of those BME680 boards connected to the I²C via a TCA9548A multiplexer and P82B96 line buffers with a supply voltage of 3.6 V. They may run equally flawlessly for up to a day, but after some (possibly shorter) time any one of them can get into an error state in which it is unable to achieve a stable heater temperature. Once it occurs, that always affects all ten temperature steps, whereas that sensor's other measurements (ambient temperature, pressure, humidity) continue to work fine. I have captured a communication cycle in the error state as well; see Scope_long.png

    How to stabilize the heater? Do I have to use longer cycles? It does not seem to depend on ambient temperature, as it usually happens at room temperature.

    The sensor is initialized like this:


    			dev_id = BME680_I2C_ADDR_PRIMARY;
    			intf = BME680_I2C_INTF;
    			/* amb_temp can be set to 25 prior to configuring the gas sensor
    			 * or by performing a few temperature readings without operating the gas sensor.
    			amb_temp = 25;
    			if (bme680_init() != BME680_OK) {
    				throw new std::domain_error("Could not initialize BME680.");
    			/* Set the temperature, pressure and humidity settings */
    			tph_sett.os_hum = BME680_OS_2X;
    			tph_sett.os_pres = BME680_OS_4X;
    			tph_sett.os_temp = BME680_OS_8X;
    			tph_sett.filter = BME680_FILTER_SIZE_3;
    			/* Set the remaining gas sensor settings and link the heating profile */
    			gas_sett.run_gas = BME680_ENABLE_GAS_MEAS;
    			gas_sett.nb_conv = 0;
    			/* Select the power mode */
    			/* Must be set before writing the sensor configuration */
    			power_mode = BME680_FORCED_MODE;
    			/* Set the required sensor settings needed */
    			uint8_t const set_required_settings = BME680_OST_SEL | BME680_OSP_SEL | BME680_OSH_SEL | BME680_FILTER_SEL | BME680_GAS_SENSOR_SEL;
    			/* Set the desired sensor configuration */
    			if (bme680_set_sensor_settings(set_required_settings) != BME680_OK) {
    				throw new std::domain_error("Could not configure BME680.");
    			/* Set the power mode */
    			if (bme680_set_sensor_mode() != BME680_OK) {
    				throw new std::domain_error("Could not set BME680's power mode.");


    Here is the code that is run in a loop to query the sensor:


    for (size_t i{0}; i < gasResistance.size(); ++i) {
    				if (_measurementEnd) {
    					struct bme680_field_data data;
    					if (bme680_get_sensor_data(&data) == BME680_OK) {
    						averageTemperature += celsius_t{data.temperature / 100.0f};
    						averagePressure += hectopascal_t{data.pressure / 100.0f};
    						averageHumidity += data.humidity / 1000.0f;
    						/* Avoid using measurements from an unstable heating setup */
    						if (dayta.status & BME680_GASM_VALID_MSK) {
    							/* Select the next gas sensor heater profile. */
    							this->gas_sett.nb_conv = overflowingNext<uint8_t, BME680_HEATER_SET_COUNT-1>(data.gas_index);
    							if (bme680_set_sensor_settings(BME680_NBCONV_SEL) != BME680_OK) {
    								ErrorObservable::notifyObservers("Next heater profile could not be selected."s);
    						} else {
                            // This is the error that keeps occurring:
    							ErrorObservable::notifyObservers("Measurement from unstable heating setup rejected."s);
    					} else {
    						ErrorObservable::notifyObservers("Data could not be acquired from device."s);
    				} else {
    					ErrorObservable::notifyObservers("Measurement had not been started."s);
    				/* Trigger the next measurement if you would like to read data out continuously */
    				if (power_mode == BME680_FORCED_MODE) {
    					if (bme680_set_sensor_mode() == BME680_OK) {
    						auto const measurementStart(std::chrono::steady_clock::now());
    						/* Calculate the total measurement duration (which takes time). */
    						uint16_t meas_period;
    						_measurementEnd = measurementStart + std::chrono::milliseconds{meas_period};
    					} else {
    						ErrorObservable::notifyObservers("Could not set sensor mode after measurement."s);



    16 REPLIES 16

    Vincent, thank you to you and the engineers. Is there more information about sequential mode? It is neither mentioned in the manual, nor in the 'old' driver code.

    Community Moderator
    Community Moderator

    the sequential mode is by default not recommend to normal user.  you have the special request and programed for 10 heat configure.  So we recommend you to use this mode.  You can find the BME68X_SEQUENTIAL_MODE in new driver.  

    The working principle is you configure all heat parameters first,  then set sensor into sequential mode,  then sensor will start measurement like "T,P,H, GAS" sequence.  and go through the heat parameters table one after the other.   After one test period,  you can read out value from data register.