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About gbeloev
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11-03-2021
11-25-2021
gbeloev
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11-04-2021
04:25 AM
Thanks. I am not asking about IAQ, eCO2, or any other calculated values, the calculation of which is apparently proprietary. All I am asking about is gas resistance measurement. This is documented in the data sheet and exposed in the open-source API, what's missing is just some recommendations on usage. Are these proprietary as well? Regards, -- Georgi
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11-03-2021
12:00 PM
Hi everyone, I implemented code to read T/P/H and gas resistance including basic compensation based on the Bosch reference code. To measure gas resistance, we have to set specific temperature and heating time. My question is: what are the recommended values and how do they affect the results? What are the pros and cons of using higher/lower temperature and longer/shorter time? Does the gas sensor react to VOCs faster/slower with different temperature/time settings? Does it recover faster/slower when exposed to clean air? Do certain VOCs absorbed (and hence measured) better/worse with different temperature settings? Do I need to sweep temperature settings, e.g, make several measurements between 200C and 400C to get a more comprehensive result? Do I need to use a certain setting intermittently, e.g., every 100 measurements at 300C do one at 400C? To clarify, I know about the BSEC library, and I already tried using it in my project. But I also want to understand how to make basic gas resistance measurements in case I don't need the features provided by the library. Thanks!
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- BME680
11-03-2021
03:35 AM
Hi, You can certainly avoid using bsec_iot_loop() in your code. I think that is just an example provided by Bosch. In my code I implemented a function to perform the equivalent functionality but without the loop. The key is to pass the current timestamp to bsec_sensor_control(), which in turn tells you if measurements should be run, and also when to run the next measurement. Then in your code use a timer or another method to delay the next call until the appropriate time. So basically (simplified): int64_t time_stamp = get_timestamp_us() * 1000ULL;
bsec_sensor_control(time_stamp, &sensor_settings);
bme680_bsec_trigger_measurement(&sensor_settings, sleep);
bme680_bsec_read_data(time_stamp, bsec_inputs, &num_bsec_inputs, sensor_settings.process_data);
bme680_bsec_process_data(bsec_inputs, num_bsec_inputs, output_ready);
int64_t time_stamp_interval_ms = (sensor_settings.next_call - get_timestamp_us() * 1000ULL) / 1000000ULL;
return (time_stamp_interval_ms > 0) ? time_stamp_interval_ms : 0; I hope this helps.
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