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Bosch Sensortec | BME688 Datasheet

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Modifications reserved |Data subject to change without notice | Printed in Germany

Document number: BST-BME688-DS000-03 Revision_1.3 022024

Figure 5: Illustration of parallel measurement mode, an example with 3 step heater profile

3.6 Measurement flow

Referring to Figure 2, the BME688 measurement period consists of a temperature, pressure and humidity measurement

with selectable oversampling. Moreover, it contains a heating phase for the gas sensor hot plate as well as a measurement

of the gas sensor resistance. In parallel mode there are 3 data registers naming Field 0, Field 1 and Field 2 which will be

filled in first in first out order.

After the measurement period, the pressure and temperature data can be passed through an optional IIR filter, which removes

short-term fluctuations. For humidity and gas, such a filter is not needed and has not been implemented.

Temperature measurement

Temperature measurement can be enabled or skipped. Skipping the measurement is typically not recommended since

temperature information is used to compensate temperature influences in the other parameters. When enabled, several

oversampling options exist. The temperature measurement is controlled by the osrs_t<2:0> setting which is detailed in

Section 5.3.3.2. For the temperature measurement, oversampling is possible to reduce the noise. The resolution of the

temperature data depends on the IIR filter (see Section 5.3.3.4) and the oversampling setting:

 When the IIR filter is enabled, the temperature resolution is 20 bit

 When the IIR filter is disabled, the temperature resolution is 16 + (osrs_t – 1) bit, e.g. 18 bit when osrs_t is set to ‘3’

Using the variables listed in Table 13, the following code will calculate the compensated temperature value (in degrees

Celsius). It is, however, recommended to use the sensor API available on github (Chapter 0) for a friendlier user

experience.

measuring

gas measuring

new data flag

gas meas index

sub meas index

meas sequence

wait

Heater profile

gas_wait_shared

Number of steps

Heating step 0

Heating step 1

Heating step 2

gas_wait_0=1

gas_wait_1=2

gas_wait_2=1

Data read by host

nb_conv = 3

Field 0 data updated

Field 0 status updated

Field 1 data updated

Field 1 status updated

Field 2 data updated

Field 2 status updated

Field 0 data updated

Field 0 status updated

Dummy gas conversion

Write '10' to mode register to start

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