Embedded Planet, Inc.
epConnected Asset | Product User Manual
Document Version: 1.0.0 | 26 Jan 22
Embedded Planet, Inc. | 31225 Bainbridge Rd Suite N, Solon, OH 44139 | 216-245-4180 | www.embeddedplanet.com |
Page 15 of 37
9.4.
Sensors | Barometer / Altimeter (U8)
The onboard barometer/altimeter option is provided by the NXP MPL3115A2. This device accommodates an
I
2
C operating frequency of up to 400kHz in fast mode. The I
2
C address is 1100000b (0x60).
More on this device can be found at:
9.4.1.
U8 | Barometer
In barometer mode, the absolute pressure sensor measures external pressure relative to a zero-
pressure reference (vacuum) sealed inside the reference chamber of the die during manufacturing.
Absolute pressure is reported as 20-bit unsigned data in Pascals and fractions of a Pascal. The value is
represented in Q18.2 fixed-point format: 18 integer bits and 2 fractional bits. 1LSB = 0.25Pa.
9.4.2.
U8 | Altimeter
In altimeter mode all pressure data is converted to equivalent altitude based on the US Standard
Atmosphere 1976 (NASA). The altitude is calculated from the pressure using the following equation:
where:
h
= altitude in meters
p
= pressure reading
p0
= sea level pressure (101,325 Pascals)
OFF_H(Register value)
= user supplied equivalent sea level pressure to compensate for local
weather conditions
Altitude data is stored as 20-
bit 2’s complement values in meters and fractions of a meter. The value is
represented in Q16.4 fixed-point format; 16 integer bits and 4 fractional bits. 1LSB = 0.0625m.
U8: Barometer / Altimeter
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