Altimetry
1. Alti/Baro
2. Waterlevel
3. Inertial
Press
UPorDN
1. Altimetry
a. MPXM2102A
b. MPL115A2
Press
UPorDN
Raw Value
0x017c1d
2(LP) value
0x017c1f
Altitude
459m
Pressure
95.365 kPa
4. Additional
‘1’
ENT
c. Experimental
‘a’
ENT
Select the MPXM2102A,
option ‘a’ for higher resolution,
amplified pressure readings
for Altimetry.
Note the way that the output is displayed. The Raw value of the
24-bit ADC value is displayed on the left. The bottom left has the
raw value after it passes two low pass filters in software. This value
is mores stable but takes longer to update.
On the right the Altitude is displayed. This is the pressure
converted to altitude in (m). The Pressure corresponding to the
ADC value is shown in the bottom right.
The board can be placed on the table. Note the Altitude
measurement as it stabilizes. Then raise it above your head as a
‘1m’ increase. The value should go up by 1m. Place on the table
again. It should drop to the original value. Place on the floor, it will
again decrement 1m. Note that ambient pressure from A/C units
can affect this value drastically.
Barometer Compensated Pressure Output
1. Altimetry
a. MPXM2102A
b. MPL115A2
Press
UPorDN
Compensated Pressure
PComp =9778 kPa
Altitude = 365 m
MPL115A2
Press ADC
Temp ADC
RawValues
6 Coefficients
74c0
6b40
0467
0428
ao = 3dc4
b1 = bd7a
b2 = c299
c11 = f8a0
c12 = 2flc
c22 = 0dc0
c. Experimental
‘b’
ENT
ENTER for Coefficients
ENT
ENT
ENT
The values for the MPL115A
are shown here. To the left are
the Pressure and Temp ADC
values in their raw form in
HEX. To the right of them are
the shifted values displayed in
decimal.
Values of the Coefficients are
shown here. These are used
for the next step in calculating
the compensated Pressure.
Compensated Pressure is
displayed. This is with an
accuracy of ±1kPa.
Press ENT to continue to the
Alarm section.
ALARM sounds when
ALARM System
Threshold is reached
Enter your Threshold
Press.
96.574 kPa
0.50
kPa
Enter for Activation
ALARM
97.324
ENT
Continued from the MPL115A
compensated Barometer
section above. Press UP and
DN to set the Alarm Threshold
in increments of 0.25kPa.
Press ENT to activate the
Alarm
Alarm is now Active. Note the
outputs of the current Pressure
in kPa, and the Alarm
Threshold point. Once
crossed, the red LED will flash
as the buzzer sounds. Try
activating by pressurizing the
MPL115A. This can be done
with a plastic syringe with
rubber tubing at the end to
make an air tight fit.
AN3956
Sensors
Freescale Semiconductor
9
FREESCALE [ Freescale ]
