Barometric Pressure and Temperature Command

Tag 0x50-0x57 command for Barometric Pressure and Temperature function are explained in this page.

Keyword

NA: Not applicable, this command should no be sent by the sensor/application.

None: No data contained in this command, data length can be set to 0x00.

Tag 0x50

Meaning: Start air pressure and temperature streaming.

Data format - app send:

Byte Length 1 1 1 1
Meaning ODR Meas Mode OSR IIR Filter

ODR (Output Data Rate): Code listed below, set how many data output per second.

Meas Mode (Measurement Mode): Code listed below, choose weather air pressure or temperature is measured.

OSR (Over Sampling Ratio): Code listed below, higher over sampling ratio increase noise performance, but also increase current consume. Higher over sampling ratio support lower max ODR. Only apply on pressure measurement, if temperature only mode is chosen, fill this with OSR 512 (code: 0x0f).

IIR Filter: Code listed below, this is used to filter out pressure glitches due to sudden pressure changes caused by events such as slamming door or wind blowing on the sensor, but also make the sensor response to changes slower.

ODR / Hz Code
1 0xff
2 0x80
4 0x40
8 0x20
16 0x10
32 0x08
64 0x04
128 0x02
256 0x01
Measurement Mode code Reply Tag tag info
air pressure only 0x01 0x56 here
air pressure only with time stamp 0x02 0x56 here
temperature only 0x03 0x56 here
temperature only with time stamp 0x04 0x56 here
air pressure and temperature 0x05 0x56 here
air pressure and temperature with time stamp 0x06 0x56 here
Over Sampling Ratio Code Max ODR Support
512 0x0f 561Hz
1024 0x1f 294Hz
2048 0x3f 151Hz
4096 0x7f 76Hz
8191 0xff 38Hz
IIR Filter Code Step Response Rate (samples)
0.2 0x02 ~2
0.3 0x03 ~3
0.4 0x04 ~4
0.5 0x05 ~6
0.6 0x06 ~8
0.7 0x07 ~12
0.8 0x08 ~20
0.9 0x09 ~45

Data format - app receive: Same as send format.

Same format will acknowledge after command is executed.

Tag 0x51

Meaning: Stop air pressure and temperature streaming.

Data format - app send:
None

Data format - app receive: Same as send format.

Same format will acknowledge after command is executed.

Tag 0x56

Meaning: Measured air pressure and temperature reply through streaming with this tag.

Data format - app send:
NA

Data format - app receive:

Byte Length 4 (optional) 4 (optional) 8 (optional)
Meaning Air Pressure Value Temperature Value Time Stamp

Air Pressure Value: Two's complement integer with 4 bytes length. Use the following equation to calculate the air pressure in kPa:

P(kPa) = (Air Pressure Value / 131072) * 40 + 70

Temperature Value: Two's complement integer with 4 bytes length. Use the following equation to calculate the temperature in C:

T(C) = (Temperature Value / 262144) * 65 + 25

Time Stamp: Unsigned Long, unit is 2.4414us. Represent the data record time. Only appear when the "with time stamp" format is chosen. This timer might not start from zero. Usually it is used to help synchronize data from multiple sensors or calculate the accurate data rate.

All optional bytes will appear when the corresponding Measurement Mode is selected.