DEMOAPEXSENSOR Freescale Semiconductor, DEMOAPEXSENSOR Datasheet - Page 14

• 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

DISSECTION OF THE ISSUES FACING THE PRESSURE READING
cycling along with airflow in the form of a breeze. Doors opening and closing change the pressure dynamic of a room as the air
flows in or out. This leads to the shifting in the zero level of the altitude as demonstrated in the flowchart.
many root causes in barometric pressure change. This is shown as an ‘experiment’ in the demo board. A straight linear pressure-
altitude can sometimes work, but generally the shifting pressure wreaks havoc on the result.
accelerometer to detect movement and re-zero altimeter readings, if pressure changes are not related to movement.
High Resolution Altimetry Customer Implementations
converted using the pressure equations 1 and 2 as seen on
have a calibration for the altitude as most customer implementations of high resolution pressure, zero a point and measure the
dynamic change in meters for a given amount of time. The following are examples of ways to implement a high resolution
altimeter with focus on the ‘dynamic’ changing pressure rather than a constant absolute altitude reading.
Altimeter Example 1:
or feet. This is a measure of the dynamic change of pressure over a short distance. This is a targeted application versus the other
application of knowing the altitude from sea level at all times after one factory calibration.
Sensors
Freescale Semiconductor
Note that with trying to resolve flowchart in
This causes the scenario of leaving the APEX on the table and seeing that the 0 foot reading shifts up and down – due to the
Multiple sensor systems can be used to possibly stabilize the result. For example, a multiple sensor system can use the
In the Altimetry screen shot as see in the
A person sets a zero point before hiking a steep hill. At the top of the hill, the change in barometric pressure is related to meters
Filtered Value
Filtered Value
Filtered Value
0ft level higher P
0ft level higher P
0ft level higher P
Filtered Value
Filtered Value
3ft level lower P
3ft level lower P
Figure 7. APEX Short Distance Calibration Routine
Calibration Section
Calibration Section
Difference in
Difference in
Difference in
Pressure
Pressure
Pressure
Quick Start
Figure
Altimetry
Raw Value
0x017c1d
2(LP) value
0x017c1f
7, there are issues as mentioned with the physical surroundings. A/C on/off
Guide, note the raw and the twice Low-Pass filtered values. These are
page 12
Altitude
Altitude
[Current Pressure –Zero Pressure Value]/3
[Current Pressure –Zero Pressure Value]/3
Resolution=
Resolution=
Resolution=
(Difference)/3ft
(Difference)/3ft
(Difference)/3ft
95.365
Altitude
Pressure
for pressure and altitude conversion. The APEX does not
in ft =
in ft =
459m
kPa
Current Pressure
Current Pressure
value stored
value stored
100ms Sample of raw
100ms Sample of raw
Pressure ? 24bit ADC
Pressure ? 24bit ADC
Twice Low-pass
Twice Low-pass
filtered value ? 18bits
filtered value ? 18bits
usable data
usable data
Constantly Running
AN3956
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