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  • Altitude Pressure EXperimental (APEX) Sensor Board

  • Created: Apr 28, 2015

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The reference design as shown is an altitude pressure experimental (APEX) sensor board. The APEX primarily functions as pressure sensor with a lot of applications. These include an altimeter and barometer. Altimetry utilizes absolute pressure sensors. An absolute sensor measures the deflection of the surrounding barometric pressure with reference to a known pressure (usually a vacuum). This allows it to compare the air pressure at sea level (101.3kPa) to the vacuum to gain an absolute pressure result. At a different elevation, the barometric (surrounding) pressure can be compared again to the vacuum for that absolute pressure result. Since both readings were taken against the same reference, they can be compared against each other. Barometric pressure does not have a linear relationship with altitude. As altitude increases, the pressure decreases.

The design makes use of the following Freescale products: MPL115A2, MPXM2102A, MPXV5004G pressure sensors with an MMA7361L accelerometer. It also utilizes Freescale's Flexis MC9S08JM60 8-bit microcontroller. The sensors with analog outputs are sampled via the JM60 microcontroller's 12-bit ADC. The exception is the MPXM2102A absolute pressure sensor. This is used for altitude so it requires a high resolution sampling. It passes through an instrumentation amplifier and then is interfaced via an external 24-bit ADC chipset before communication via SPI to the JM60 MCU. The JM60 interfaces with the LCD screen and processes inputs by the user for the output display .

The APEX is useful in a wide variety of applications including altimeter, barometer, barometer alarm, weather station, water level, water level alarm, tilt, freefall, and temperature sensing.