DEMOAPEXSENSOR Freescale Semiconductor, DEMOAPEXSENSOR Datasheet - Page 15

• Manufacturer Part Number: DEMOAPEXSENSOR
• Description: BOARD DESIGN ALTITUDE PRESSURE
• Manufacturer: Freescale Semiconductor

Specifications of DEMOAPEXSENSOR

• Sensor Type: Accelerometer, Pressure, Water Level, Altimeter/Barometer
• Sensing Range: Multiple Ranges
• Interface: I²C, SPI, Analog
• Sensitivity: Multiple
• Voltage - Supply: 10 V
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: MPX2102, MPXV5004G, MPL115A2, MMA7361L
• Acceleration: 6 g
• Sensing Axis: Triple Axis
• Output Type: Digital
• Interface Type: I2C, SPI
• Operating Voltage: 16 V
• Operating Current: 10 mA
• Leaded Process Compatible: Yes
• Peak Reflow Compatible (260 C): Yes
• Rohs Compliant: Yes
• Silicon Manufacturer: Freescale
• Silicon Core Number: MPXM2102A, MPXV5004G, MPL115A2, MMA7361L
• Kit Application Type: Sensing - Sampling Kit / Related Components
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: MPL115A, MPXM102A, MPXV5004G

Altimeter Example 2:
beginning ‘zero point’ is 300 m. Entering the building the pressure sensor starts measuring the elevation, and tries to calculate
the height in meters.
Issues in this Example for Consideration:
MPL115A Miniature Barometer DEMOAPEXSENSOR
pressure range of 50 to 115 kPa. This narrower range is more application specific for events occurring in that altitude or in devices
requiring that pressure. In this section, the DEMOAPEXSENSOR’s implementation of the MPL115A and the information
displayed on the APEX is described.
of the MPL115A in screen shots of the DEMOAPEXSENSOR.
MPL115A Digital Barometer. Essentially in the LCD screen shots above, the Raw values of Pressure and Temperature are
displayed in Hexadecimal and Decimal format. Following this, the six coefficients MSB+LSB are shown in Hex format. The
combination of this data (streamed via I
Using eq. 2, the altitude is calculated and shown in meters.
any calibration trim, or offset auto zero. The Pcomp spec for the MPL115A is such that the value has an accuracy of ± 1kPa. The
advantage is implementing the sensor and having the compensated pressure readings without any additional calibration etc. on
the customer side.
stored in MPL115A registers. Padc and Tadc are the raw ADC values of Pressure and Temperature that are clocked out of
MPL115A digitally.
Sensors
Freescale Semiconductor
A GPS equipped smart-phone loses GPS signal as it enters a building. Knowing the approximate elevation with the GPS, the
The MPL115A is a small 5 x 3 x 1.2 mm digital absolute pressure sensor. It is available in either I
In the
The MPL115A’s Implementation is described in detail in the Application Note AN3785; How to Implement the Freescale
The Pcomp value is the compensated absolute pressure value. This value unlike the analog pressure sensors does not require
As stated in AN3785, the MCU has to apply the equation below for Pcomp given that a0, b1, b2, c11, c12, c22 are coefficients
• When entering a building from outside, a sudden rise in pressure is highly probable. This will send two different scenarios.
• Buildings vary on height per a floor. Lobbies of sky-rises have higher ceilings. Hotel accommodation floors tend to have
• Large buildings can be pressurized or not. It depends on building design. Some stadiums for sporting events are
• Smart use of Altimetry in tall buildings would use building information stored in a ‘smart’ GPS device so the altitude can
It could signify that the user has ‘fallen’ in altitude by several meters (such as jumping off a building or small cliff). Or they
have entered into a building with significant pressurized airflow (typical of an air-conditioned lobby with high air flow).
shorter standard heights. A restaurant located halfway or on top of the building may have a higher ceiling. The main point
is that the altitude in meters does not ideally correspond to floor location.
pressurized to keep a fabric roof afloat. Tall high-rises have multiple stages of air-conditioning units. This leads to varied
pressure per a floor depending on that section’s on/off cycle, fan speed, or the air-tight nature of that section. Elevator
shafts also can equalize pressure, or create some pressure change as elevators move up and down.
translate to floor level. This way location based services, emergency 911, etc. can know which floor the user is located.
Quick Start Guide
Barometer Compensated Pressure Output
MPL115A2
Press ADC
Temp ADC
ENTER for Coefficients
Stage 1
Raw Values of Temperature
and Pressure displayed on
LCD screen.
Pcomp
section, the “Barometer Compensated Pressure Output” describes the compensated Pressure output
Raw Values
74c0
6b40
=
a0
+
2
(
0467
0428
C or SPI from the MPL115A) is used at the host MCU to calculate the Pcomp value.
b1
+
cl Padc
⋅
6 Coefficients
ao = 3dc4
b1 = bd7a
b2 = c299
Stage 2
Display of 6 coefficients listed
on LCD screen.
+
c12 Tadc
⋅
c11 = f8a0
c12 = 2flc
c22 = 0dc0
)
⋅
Padc
+
(
b2
Compensated Pressure
PComp
Altitude = 365 m
Stage 3
Display of Compensated
Pressure output in kPa units.
+
c12
⋅
=9778
Tadc
) Tadc
kPa
⋅
2
C or SPI version. It has a
(eq. 3)
AN3956
15