Gas resistance values from BME688 on Thingy:53

Question

I'm interested in using the gas detector on the BME688 on my Thingy53. I've compiled and run zephyr/samples/sensor/bme680 using nRF Connect toolchain 2.3.0, and it produces reasonable output for temperature, pressure, and humidity. However the gas detector resistance value printed seems very high (more than 12 megaohms) and is unchanging, even when I breathe on it or put it in a sealed container with a few ml of isopropanol. 
 
 Does the Zephyr driver need to be updated to deal with differences between the 680 and the 688? This Bosch FAQ seems to suggest so. I understand there will be additional work required to use Bosch's fancy proprietary models, but I'd like to just see if the hardware is working. 
 Any suggestions for next steps? 
 Other tickets I found on DevZone: 
 Similar problem with stuck values , apparently unresolved. 
 A (partially?) successful attempt to use Bosch libraries , but no confirmation of success reading gas values.

rtlab_hmkang · Answer

Hi DougR I had a same problem. There's small difference between bme680 and bme688's register map. If you want to use gas sensor, you should set "run_gas" register in GAS_1_CTRL (0x70). However, ncs-zephyr's driver (which is in this directory : zephyr/drivers/sensor/bme680/bme680.c) doesn't set the "run_gas" bit field. Because It's been to long that I figured this problem, I'm not sure the register's address and value was correct. But I ensure that it is not appropriate to use directly zephyr's bme680 driver to bme688. I changed the source like this which are in "zephyr/drivers/sensor/bme680" =========== ORIGIN =========== bme680.c err = bme680_reg_write(dev, BME680_REG_CTRL_HUM, BME680_HUMIDITY_OVER); if (err < 0) { return err; } err = bme680_reg_write(dev, BME680_REG_CONFIG, BME680_CONFIG_VAL); if (err < 0) { return err; } err = bme680_reg_write(dev, BME680_REG_CTRL_GAS_1, BME680_CTRL_GAS_1_VAL); if (err < 0) { return err; } err = bme680_reg_write(dev, BME680_REG_RES_HEAT0, bme680_calc_res_heat(data, BME680_HEATR_TEMP)); if (err < 0) { return err; } bme680.h #define BME680_CHIP_ID 0x61 #define BME680_LEN_FIELD 15 #define BME680_LEN_COEFF_ALL 42 #define BME680_LEN_COEFF1 23 #define BME680_LEN_COEFF2 14 #define BME680_LEN_COEFF3 5 =========== NEW =========== bme680.c err = bme680_reg_write(dev, BME680_REG_CTRL_HUM, BME680_HUMIDITY_OVER); if (err < 0) { return err; } err = bme680_reg_write(dev, BME680_REG_CONFIG, BME680_CONFIG_VAL); if (err < 0) { return err; } // err = bme680_reg_write(dev, BME680_REG_CTRL_GAS_1, // BME680_CTRL_GAS_1_VAL); // if (err < 0) { // return err; // } err = bme680_reg_write(dev, BME680_REG_CTRL_GAS_0, 0); // BME68X_ENABLE_HEATER 0x00 if (err < 0) { return err; } uint8_t gas_1_ctrl_val; gas_1_ctrl_val = BME680_CTRL_GAS_1_VAL | 0xa0; err = bme680_reg_write(dev, BME680_REG_CTRL_GAS_1, gas_1_ctrl_val); if (err < 0) { return err; } err = bme680_reg_write(dev, BME680_REG_RES_HEAT0, bme680_calc_res_heat(data, BME680_HEATR_TEMP)); if (err < 0) { return err; } bme680.h // #define BME680_LEN_FIELD 15 #define BME680_LEN_FIELD 17 #define BME680_LEN_COEFF_ALL 42 #define BME680_LEN_COEFF1 23 #define BME680_LEN_COEFF2 14 #define BME680_LEN_COEFF3 5 Check the datasheet and register map I enveloped. bme688 --> BME688 Datasheet (bosch-sensortec.com) bme680 --> Newsletter-Template-DE (adafruit.com) Sincerely,

wass · Answer

Hi, I have a developed a Thingy53 project https://github.com/HomeSmartMesh/sdk-hsm-thingy53 where I ported the BME688 vendor driver BME68x-Sensor-API to Zephyr. I also ported the vendor library to read the IAQ with their .a library Bosch-BSEC2-Library. It is not based on the existing Zephyr BME680 which does not work, but this is a complete rework which consists of : 
 
 BME688 Zephyr Driver : in hsm/drivers/sensor/bme688 
 
 BME68x-Sensor-API vendor driver integration https://github.com/boschsensortec/BME68x-Sensor-API 
 Using Zephyr's Sensor API in C language for usage in BME688 simple forced mode 
 Driver extension functions to use BME688 in Parallel mode and get all x10 gas measures

BME688 Server : in hsm/subsys/bme688_server 
 
 C++ wrapper to configure the BME688 usage in json structure (temperatures profile and durations) 
 handler delivers the sensor results in a json structure (temperature, humidity, pressure, gas-0..gas-9) 
 Bosch-BSEC2-Library .a vendor's binary integration for IAQ (Indoor Air Quality) measurements https://github.com/boschsensortec/Bosch-BSEC2-Library

The project has also the following, which makes it easy to use it in real case application 
 
 Mesh Network with OpenThread broadcasting UDP packets as client and running a sensors server. 
 C++ application with json inputs for config and outputs for sensors enables direct mapping to MQTT 
 RGB Led, Light color, Battery 
 
 See all samples, each one is a simple step project to check if things are working, 05_bme688, 06_bme688_parallel, 07_bme688_parallel_cpp, 08_bme688_bsec2 and 20_sensors_server which combines all features together. I'm currently deploying and testing this project at home, if you or someone still have questions or feedback, let me know. Here an overview about the driver and library integration, more details on the project readme.