AN3956

AN3956 FREESCALE | Alldatasheet

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© Freescale Semiconductor, Inc., 2009. All rights reserved. Figure 1. Basic Components of APEX Board Table 1. On-Board Sensors

3 Axis low-g

Figure 2. Simplified Block Diagram inputs by the user for the displayed output. Several Algorithms are used to calculate functions on the DEMOAPEXSENSOR. AN3785, How to Implement the Freescale MPL115A Digital Barometer. AN3914, Modern Altimeter and Barometer System using the MPL115A. More pressure sensor application notes can be found at: www.freescale.com/pressure.

3 Axis XYZ

Figure 3. A A B B C C D D E E F F G G H H I I J J 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 PTA4 PTA3 PTA2 PTA1 PTA0 PTG1/KBIP1 PTG0/KBIP0 VUSB33 USBDP USBDN VSS VDD PTE7/SS1 PTE6/SPSCK1 PTE5/MOSI1 PTE4/MISO1 PTE3/TPM1CH1 PTE2/TPM1CH0 PTE1/RxD1 PTE0/TxD1 PTF6 PTF5/TPM2CH1 PTF7 PTC6 PTF4/TPM2CH0 PTF3/TPM1CH5 PTF2/TPM1CH4 PTF1/TPM1CH3 PTF0/TPM1CH2 Reset IRQ/TPMCLK PTC4 PTA5 PTB0/MISO2/ADP0 PTB1/MOSI2/ADP1 PTB2/SPSCK2/ADP2 PTB3/SS2/ADP3 PTB4/KBIP4/ADP4 PTB5/KBIP5/ADP5 PTB6/ADP6 PTB7/ADP7 PTD0/ADP8/ACMP+ PTD1/ADP9/ACMP- VDDAD VREFH VREFL VSSAD PTD2/KBIP2/ACMP0 PTD3/KBIP3/ADP10 PTD4/ADP11 PTD5 PTD6 PTD7 PTG2/KBIP6 PTG3/KBIP7 BKGD/MS PTG4/XTAL PTG5/EXTAL VSSOSC PTC0/SCL PTC1/SDA PTC2 PTC3/TxD2 PTC5/ExD2 M C 9 S 0 8 J M 6 0 DB6 DB5 DB4 DB3 DB2 DB1 DB0 E R/W RS Vo Vdd Vss L C D DB7 A K Vout GND Vs NC NC NC NC NC M P X V 5 0 0 4 USB DB0 DB1 DB2 DB3 DB4 DB5 DB6 DB7 DB0 DB1 DB2 DB3 DB4 DB7 DB5 DB6 E RW RS +5V +5V C7 0.1μF 10K ! R9 +5V 0.1μF 10M ! R12 22pF C18 22pF C17 0.1μF 0.1μF +5V Gnd NC Gnd Vo L M 2 0 C28 0.1μF C20 0.1μF R20 470 ! C26 470pF C24 .01μF C25 0.1μF R17 1K ! R18 1K !R19 1K ! C23 0.1μF C22 0.1μF C21 0.1μF +3.3V C29 0.1μF AK R15 5.1K ! R11 10K ! R10 C14 0.1μF +5V RESET 10K ! R4 +5V 5.1K ! R5 0.1μF E RW RS BDM 10K ! R2 +5V 5.1K ! R3 0.1μF ENT DN UP ESC 10K ! R21 C27 0.1μF +5V AK R16 AK R13 AK R14 5.1K ! R22 C15 0.1μF C19 0.1μF +VAref +5VA +5VA +5VA PTD1 PTD0 ADP7 ADP6 ADP5 PTG0 PTG1PTA2 PTA3 PTA4 SDA SCL PTC5 PTC3 PTD1 PTD0 ADP7 ADP6 ADP5 PTA2 PTA3 PTA4 PTG0 PTG1 PTE0 PTE1 PTE2 PTC6 PTC5 PTC3 SDA SCL 33 ! 33 ! +5V 0.1μF 10μF C11 0.1μF C12 10μF +5VA +VAref C13 0.1μF SDA SCL +5V C16 1μF C10 0.1μF CH3 CH2 CH1 CH0 0.1μF /CS BUSY SDO SDI SCK ADC_control 2-H6 CH 2-H7 +3.3V R26 20K ! NP Buz 2-D1 Vin /SLEEP VSS VDD SELF_TEST g_sel Zout Yout Xout 0g_det M M A 7 3 6 1 U12 SHDN GND CAP VDD CS DOUT DIN SCLK M P L 1 1 5 A 2 U11 C47 1μF +5V 2 1 PTE0 PTE1 PTE2 PTC6 BAT54SLT1GOSCT +5V

Figure 4. A A B B C C D D E E F F G G H H I I J J 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 OUTB -INB -INA OUTA ADCINA ADCINB COM CH3 CH2 CH1 CH0 REF- REF+ +INB +INA MUXOUTA MUXOUTB INT-/EXT FO BUSY SDI SDO SCK /CS Vcc V+ GNDGNDGND V- L T C 2 4 4 2 +5V C42 0.1μF +5VA C45 0.1μF Vin+ Vin- Rg Vrf Vo Rg2 I N A 1 1 8 U B U4511 ! R24 +5VA C33 0.1μF CH1 CH2 CH3 CH0 C37 0.1μF C38 0.1μF +VAref C36 0.1μF /CS SCK SDO SDI BUSY -Vout Vs +Vout GND M P X M 2 1 0 2 A U5 C30 0.1μF R23R23 ADC_control 1-C5 CH 1-B6 P N SW7 P N C31 47μF C32 0.1μF 3U7 MIC520I-5.0YS 3U10 MIC520I-3.3YS P N C34 47μF C39 0.1μF P N C35 47μF C40 0.1μF +3.3V +5V L14806E101R-10 P N C43 47μF C44 0.1μF +5VA R25 470 ! C41 0.1μF D7 LM4040A41IDBZR +VAref 1-E6 Vin 91 ! C46 0.1μF D8 LM4040A41IDBZR

ON/OFF Switch: Located on the left side, under the LCD screen along the PCB edge. It is a slide switch. Menu Selection Buttons: Located on the right side, next to the blinking LEDs. Figure 5. APEX Controls

Screen 3: Screen 4: Screen 5: Screen 6: Screen 7: PPL115A2 Raw Values Press ADC 5bc0 Temp ADC 7a00 ENTER for Coeff. 0367 Pressure and Temperature Raw Values in decimal 0488 format are on the right in blue. Press ENT menu Button one time to move forward to see the coefficients.

6 Coefficients:

Coefficients are listed. Press ENT menu button to see b8 93 compensated pressure reading. Compensated Pressure PComp = Pressure is compensated and listed in kPa. Press ENT 97.273 to continue to Alarm System. To navigate backwards, press ESC to cycle to previous screen. ALARM System 0.50 kPa Press UP or DN to set Pressure Threshold for the Alarm ENTER for Activation System in 0.25 kPa increments. Press ENT to activate the alarm feature and wait for the buzzer to sound. Enter your Threshold ALARM sounds when 97.273 kPa Alarm is armed and the current pressure is shown on top. ALARM The bottom is the threshold pressure for the alarm. Note the RED LED activates with the alarm and a green solid LED indicates a non alarm pressure. Threshold is reached Press.

97.836 To navigate backwards: press ESC to cycle to previous

screens and deactivate alarm.

Functions and the Screen Shot Navigation Path Color Legend Inputs: User has to enter in a value, or select a choice, UP or DN. Typical inputs are shown in ‘x’ format. ESC repeatedly pressed, exits user to main menu. Outputs: Demo code returns a result or value based on the user inputs. Simple Weather Station 1. Alti/Baro Press 2. Waterlevel UPorDN 3. Inertial 4. Additional ‘4’ Additional Press a. Weather UPorDN b. Weather Advanced c. Temp Sensor ‘a’ Please enter your Altitude (m) UP/DN 00 m 101.3 kPa SIMPLE WEATHER Weather outlook 0.423 kPa Sun/Cloud Symbol This is the altitude at your current location. Once its entered, the value of Pressure for that altitude is displayed. The current Weather outlook is displayed in the options of Symbols: Sun, Rain, Sun/Cloud. Note the difference in pressure is displayed from current to Altitude. Advanced Weather Station 1. Alti/Baro Press 2. Waterlevel UPorDN 3. Inertial 4. Additional ‘4’ Additional Press a. Weather UPorDN b. Weather Advanced c. Temp Sensor ‘a’ WEATHER Sun/Cloud Min 0224 dP/dt -0.042 Stable Weather Pattern This shows the weather in the top right corner from the simple weather algorithm. The ‘Min’ shows how long the algorithm is working in minutes. dP/dt shows the differential change per an hour. The corresponding weather type is predicted in the bottom. This takes readings for up to 3 hours and compares results to the algorithm every ½ hour. Waterlevel Sensing 1. Alti/Baro Press 2. Waterlevel UPorDN 3. Inertial 4. Additional ‘2’ 2. Waterlevel MPXV5004 Integrated 40cm H2O Level Press ENTER 2. Waterlevel Press a. Liquid (cm) UPorDN b. Alarm system ‘a’ Place in Liquid ADC 12bit 1179 H2O Level 0.0 cm Pressure 0.0 kPa Selection of the Liquid Waterlevel section in ‘a’. Place tube attached to MPXV5004 into water. As it goes into the water, the value of water height will be displayed on the screen along with Pressure. ENT ENT ENT ENT ENT ENT ENT ENT

Waterlevel Alarm (sub-option from above menu) 2. Waterlevel Press a. Liquid (cm) UPorDN b. Alarm system ‘b’ Alarm System Enter your Threshold 5.50 cm ENTER for Activation LARM sounds when Threshold is reached Press. 4.00 cm ALARM 5.50 Press UP and DN to set the Alarm Threshold in increments of 0.25cm. Press ENT to activate the Alarm. Alarm is now Active. Note the outputs of the current Pressure in cm, and the Alarm Threshold point. Once crossed, the red LED will flash as the buzzer sounds. Try activating by moving the tube up and down in a column of water. Temperature Sensor 1. Alti/Baro Press 2. Waterlevel UPorDN 3. Inertial 4. Additional ‘4’ Additional Press a. Weather UPorDN b. Weather Advanced c. Temp Sensor ‘c’ Temperature External Temp Sensor

1487 ADC

031 Deg C 087 Deg F

Value of the External Temperature sensor is displayed on the screen in °C and °F Inertial Sensor 1. Alti/Baro Press 2. Waterlevel UPorDN 3. Inertial 4. Additional ‘3’ 3. Inertial MMA7361L 3 Axis Accelerometer 1.5g Press ENTER TRaw Values of Accel X axis 1594 Y axis 1663 Z axis 2388 Tilt Angle X axis -2deg Y axis -4deg Z axis 90deg ADC values of the MMA7361L are displayed on the screen. Press Enter to proceed to the next screen ADC values are converted and displayed on the screen as an angle for X, Y and Z axis. Press Enter to continue to Free Fall Detection. Free Fall detect Drop carefully in Linear Free Fall only. FF detected!! Drop board in linear manner to hear buzzer detecting Free Fall condition, and Red LED will blink with buzzer. Exit Free Fall and Inertial by pressing ESC. ENT ENT ENT ENT ENT ENT ENT ENT

1. Alti/Baro Press 2. Waterlevel UPorDN 3. Inertial 4. Additional ‘1’ 1. Altimetry Press a. MPXM2102A UPorDN b. MPL115A2 c. Experimental ‘a’ Raw Value Altitude 0x017c1d 459 m 2(LP) value Pressure 0x017c1f 95.365 kPa 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 Press a. MPXM2102A UPorDN b. MPL115A2 c. Experimental ‘b’ MPL115A2 RawValues Press ADC 74c0 0467 Temp ADC 6b40 0428 ENTER for Coefficients

6 Coefficients

ao = 3dc4 c11 = f8a0 b1 = bd7a c12 = 2flc b2 = c299 c22 = 0dc0 Compensated Pressure PComp =9778 kPa Altitude = 365 m 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 System Enter your Threshold 0.50 kPa Enter for Activation ALARM sounds when Threshold is reached Press. 96.574 kPa ALARM 97.324 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. ENT ENT ENT ENT ENT ENT ENT

not calibrated. This is typical of end application requiring a starting point. used for data-acquisition systems. Thus, the span is really only 16.38 mV at 4.096 V, for a pressure range of 0 to 100 kPa. MPXM2102A is on a separate shunt such that no other connected IC will induce additional noise on the shared line. Table 2. Operating Characteristics (VS = 10 VDC, TA = 25°C unless otherwise noted, P1 > P2)

stable measurement. The ADC has to be greater than 16-bits to gain 3 foot intervals in measurement. capacitance that creates noise. Analog 5 V has its own separated section from the digital 5 V in the power layer of the layout. This minimizes the noise on both 5 V digital and 5 V analog sections. reduce A/C and breeze effects on the pressure sensor. Most applications of such, include a housing perforated with small holes. a demo board, has no such housing. since it is included in the result. they can be compared against each other. reference points are given in Table 3. Figure 6. Altitude vs. Pressure Table 3. Reference Points

Freescale Semiconductor 12 At low elevations, a square meter on the earth’s surface has greater weight above it than at higher altitudes. This is due to the mass of water vapor and air that sits upon it. Imagine cubes of air and water vapor stacked from the ground to space. At the low altitude there is more cubic mass above, while higher altitudes will have less of these stacked above it. Air and water vapor will compress more at sea level and the air is significantly denser than at high altitude. The density is not uniform with altitude, and thus the pressure is not either. The reason for altitude’s non-linear relationship is that air has infinite compressibility. It disproportionately compresses more as weight is placed upon it. Hence the graph of Pressure vs. Altitude seen in Figure 6. The simplified mathematical equation used to calculate altimetry in Table 3 is: Assuming p0 = 101.3 kPa ph - Pressure at height h po - Initial Pressure point at sea level or 101.3 kPa Calculations for a 24-bit ADC First: Figuring out how the 24-bit ADC translates to counts, followed by pressure and altitude. 24-bit ADC LTC2442 reference voltage is 4.1 V (temperature and voltage stable shunt). MPXM2102A has a 16.4 mV span @ 4.1 V supply. Output is gained x 98.8 by instrumentation amplifier. Span of differential amplified signal is now 1.62 V. Low pressure end of 0 kPa input is approximately 0 V seen at the differential amplifier output. Conversely the higher end of the pressure reading at 100 kPa is = 1.62 V. SPAN of MPXM2102A after Differential Instrumentation Amplifier is now 1.62 V. The 24-bit ADC would have a resolution of 4.1V/16777215 counts or 0.244 V per an ADC count. Since the differential span of the sensor is 1.62 V after the amplifier, the span of 0 to 100 kPa can be seen as a ADC value of 0 counts to 6629045 counts. This makes each ADC count equivalent to 0.0000151 kPa or 0.0151 Pa. The LTC2442’s value was shortened to a 18-bit conversion to minimize the baseline noise seen on the ADC output. For an 18-bit ADC conversion, 4.1V/262143 equals a resolution of 15.6 V per a single ADC count. Since the differential span of the sensor is 1.62 V after the amplifier, the span of 0 to 100 kPa can be seen as a ADC value of 0 counts to 103846 counts. This makes each ADC count for the pressure span equivalent to 0.000963 kPa or 0.963 Pa. Table 4. ADC Resolution Range of ADC Counts 8-bit 0 to 255 12-bit 0 to 4095 16-bit 0 to 65,535 18-bit 0 to 262,143 24-bit 0 to 16,777,215 h 18400m log ⋅= ph p0 e (eq. 1) (eq. 2)

Freescale Semiconductor 13 Summarizing in Table 5 DEMOAPEXSENSOR can read a 0.000963 (kPa/ADC count) step for a 0 to 100kPa MPXM2102A sensor. The formulas earlier were shown to reference the pressure to altitude relationship. Converting all this to altitude: Reviewing Table 6, the DEMOAPEXSENSOR has code written to interpret small pressure changes and convert these to altitude. The conversion from pressure to altitude still has to use the exponential equation for a proper conversion. But the approximate distances and the ADC count equivalent are shown here. These are approximate across the pressure range but as written in the demo code, the pressure is determined first, the altitude second. The altitude is calculated via the pressure value inserted into the exponential altitude-pressure formula. Experimental Altimetry Section The preceding section on Altimetry has used the pressure sensor value to convert the pressure to an altitude reading. This value of pressure is not linear with vertical height as detailed in the graph of Figure 6. However if a curved line is magnified enough, the end result can be treated as a straight line. The “Experimental” section of the Altimeter/Barometer tries this particular method. Due to changing air currents and unstable smaller resolution, it may require outdoor demonstration to get better results. In this example the chart outlines the calibration routine.

• To calibrate the part, first place the boar d on the floor or table in front of you.
• Wait until the low pass filtered val ue is stable then press Enter. This saves the “0 level” barometric pressure.
• Following this, place the board about 3 feet a bove the “0 level”. Either this is at waist height if previously on the floor, or above your head if previously on the table. When the value stabilizes, press Enter again. Now the display will output the distance in smaller increments than 1 foot. Notice how it tends to jump around, and the “0 level” shifts. This Experimental section shows how this method while being more accurate is not as stable as the exponential method to see pressure. The resolution is reasonable for a short period of time before barometric changes in pressure change the calibration. Table 5. ADC Type Resolution (V/ADC) Resolution (kPa/ADC) 24-bit 0.244 V 0.0000151 kPa 18-bit 15.6 V per 1 ADC count 0.000963 kPa per 1 ADC count Table 6. Distance Pressure (mB) Pressure (kPa) Voltage Change (V) ADC (counts) 1 m 0.11 0.011 1.78 11.4 so ~11 3 ft 0.09 0.009 1.46 9.35 so ~9 1 ft 0.03 0.003 0.49 3.11 so ~3

Figure 7. APEX Short Distance Calibration Routine flows in or out. This leads to the shifting in the zero level of the altitude as demonstrated in the flowchart. 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. altimeter with focus on the ‘dynamic’ changing pressure rather than a constant absolute altitude reading. application of knowing the altitude from sea level at all times after one factory calibration.

Freescale Semiconductor 15 Altimeter Example 2: A GPS equipped smart-phone loses GPS signal as it enters a building. Knowing the approximate elevation with the GPS, the 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:

• When entering a building from outside, a sudden rise in pressure is highly probable. This will send two different scenarios. 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).
• Buildings vary on height per a floor. Lobbies of sky-rises ha ve higher ceilings. Hotel accommodation floors tend to have 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.
• Large buildings can be pressurized or not. It depends on building design. Some stadiums for sporting events are 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.
• Smart use of Altimetry in tall buildings would use building in formation stored in a ‘smart’ GPS device so the altitude can translate to floor level. This way location based services, emergency 911, etc. can know which floor the user is located. MPL115A Miniature Barometer DEMOAPEXSENSOR The MPL115A is a small 5 x 3 x 1.2 mm digital absolute pressure sensor. It is available in either I2C or SPI version. It has a 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. In the Quick Start Guide section, the “Barometer Compensated Pressure Output” describes the compensated Pressure output of the MPL115A in screen shots of the DEMOAPEXSENSOR. The MPL115A’s Implementation is described in detail in the Application Note AN3785; How to Implement the Freescale 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 I2C or SPI from the MPL115A) is used at the host MCU to calculate the Pcomp value. Using eq. 2, the altitude is calculated and shown in meters. The Pcomp value is the compensated absolute pressure value. This value unlike the analog pressure sensors does not require 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. As stated in AN3785, the MCU has to apply the equation below for Pcomp given that a0, b1, b2, c11, c12, c22 are coefficients stored in MPL115A registers. Padc and Tadc are the raw ADC values of Pressure and Temperature that are clocked out of MPL115A digitally. Barometer Compensated Pressure Output MPL115A2 RawValues Press ADC 74c0 0467 Temp ADC 6b40 0428 ENTER for Coefficients

ao = 3dc4 c11 = f8a0 b1 = bd7a c12 = 2flc b2 = c299 c22 = 0dc0 Compensated Pressure PComp =9778 kPa Altitude = 365 m Stage 1 Stage 2 Stage 3 Raw Values of Temperature and Pressure displayed on LCD screen. Display of 6 coefficients listed on LCD screen. Display of Compensated Pressure output in kPa units. Pcomp a0 b1 cl Padc c12 Tadc ⋅+⋅+()+ Padc b2 c12 + Tadc⋅() Tadc⋅+⋅= (eq. 3)

following is a possible sequence for the calculation Pcomp, the trimmed pressure output. Input values are in bold. longer intervals etc. to give the illusion of a more stable value. Here it is shown simply to get an idea of the raw conversion result. The MPL115A can be used to measure changes in vacuum or for barometric pressure rather than the MPXM2102A. Ziploc bag or syringe with a soft applicator tip useful in activating the alarm. MPL115A. The delta in the value is compared in the Table 7. This is typical of a simple application and the APEX simulates a desktop barometer that is commonly bought at retailers. a 3 hour period. This is outlined in Table 8 (AN3914). Table 8. Advanced Weather Determination

Freescale Semiconductor 19 Inertial MMA7361L The DEMOAPEXSENSOR has a quick implementation of the 3 axis selectable low-g accelerometer. Notably the demo board implements the tilt function of the accelerometer and Free Fall detection. The Quick Start Guide shows the modes to select either function. TILT ANGLE ON THE DEMOAPEXSENSOR The ADC counts are converted to tilt angles using the equation below: Where: Vout = Analog output of accelerometer Voff = Offset voltage of accelerometer V/g = Sensitivity 1.0g = Earth’s gravity θ = Tilt Angle Note: MMA7361 was set to a g-level of 1.5 g. Offset voltage is typically 1.65 V @ 3.3 V biasing supply FREE FALL DETECT ON THE DEMOAPEXSENSOR Free Fall detect is the situation where all three axes of the inertial sensor converge towards the offset or ‘0g’ range. This is also given as an output on the MMA7361L as the 0g-Detect pin. ‘1’ or logic high is the output for a detected Free Fall. Note that this is also for Free Fall in a linear fashion such that the board is not spinning or in rotation as it falls. The DEMOAPEXSENSOR emits a buzzer noise and a flashing red LED as the Free Fall detect occurs. Vout Voff ΔV ⎛⎞+= (eq. 4)

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