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About mjanke
since
07-18-2019
03-19-2022
mjanke
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4
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11-23-2021
05:12 PM
Hi @BSTRobin, I we are using the BME 688 chip on our custom device. Yes, I followed the example code that you linked. It works fine for a single forced mode read of tph. My challenge is that I am doing multiple reads - every few min. I will be changing code to read every hour, so forced mode with manual timed tph reads is required. The example does not show repeated forced mode reads (e.g. every few min). Do I have to config before each read to get humidity data? Seems strange as I can read temp and pressure without config before each read. Regards, Mark J
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11-23-2021
01:56 AM
Hi, I can successfully setup a tph read using the following function call sequence as per the forced mode example: init_I2c (my fcn to init my i2c link) bme68x_set_conf (setup a config in which I am sampling 1x for temp and press and 8x for humidity, no filter or odr) bme68x_set_heatr_conf (with heater disabled) bme68x_set_op_mode (to enable forced mode read) bme68x_get_meas_dur (to get the read delay) ... wait the read delay ... about 25 mSec bme68x_get_data (read the data) All data seems valid and accurate. Temp is 21 degC, pressure is just over 100 kPa, and RH is 46 percent. This matches other sensors nearby. I then try and repeat forced reads every min by repeating bme68x_set_op_mode (), bme68x_get_meas_dur(), wait, bme68x_get_data() every min. ... and both temp and pressure data looks good, but humidity always reads 100 percent. If I execute bme68x_set_conf(), bme68x_set_heatr_conf() with heater still off, bme68x_set_op_mode (), bme68x_get_meas_dur(), wait, bme68x_get_data() every min, all data looks ok. Why do I need to set configs each time in order to get valid humidity data? Thanks in advance. Mark J
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11-05-2021
05:02 PM
Hi @BSTRobin, Please see my original note. We would like to get down to 5 uA (or lower). I realize that better performance results from a higher ODR, but if that uses a battery in far less time, there will be no point as our customer won't accept this. Please consider that increased battery life is key in this application. I expect that 12.5 Hz will be ok if the duration of an event is >= 300 mSec. My challange is determining what the current draw will be at ODR of 12.5 Hz and Vdd of 3.3 Vdc. Thanks, Mark J
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11-04-2021
10:27 PM
Hi, We are successfully using the significant motion feature to generate an interrupt. We have come across and application requiring better battery efficiency and we want to ensure that we setup sig motion for the lowest possible uA draw while still being able to detect a bump on the BMI270. Think a sharp drop or bump with duration of 300mSec or more and g-force of 3g or more. Table 1 in Section 1 of the BMI270 datasheet indicates 10 uA for Vdd of 1.8 and ODR of 25 Hz (40mSec sample time). To measure bumps lasting 300 mSec or more, I think we can drop the ODR to 12.5 Hz. Will that drop the current much below the 10 uA? Even 5 uA would make a large difference for our battery efficiency. Also, we are using a Vdd of 3.3 Vdc, does that mean less current is required (ie the chip uses a consistent power level, so increasing Vdd reduces the current for the same functionality)? Thanks, Mark J
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09-29-2021
12:43 AM
Hi Minhwan, After digging into what VOCs would be appropriate and expected levels of those VOCs within human breath, I have come to the conclusion that really only Ethanol and Methanol are useful. Other VOC concentrations are simply too low and not repeatable. To use Ethanol and Methanol I will have to teach the AI with quite low concetrations. I was expecting approx 10-20 ppb for each to indicate low values and 100-200 ppb to indicate high values. Note that is parts per billion and not parts per million. The critical question - is the BME 688 able to measure concentrations of Ethanol and Methanol in such low concentrations? Even if this is yes, testing against some accurate measurment will be difficult as a complicated and expensive device like a mass spectrometer may be requried. Regards, Mark J
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