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 TE Connectivity

  • Wrist Mount Digital Altimeter

  • Created: Sep 13, 2015

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This project is a simple wrist mount digital altimeter which is a device used to determine altitude. This design uses atmospheric pressure to calculate the altitude of its location. The lower the atmospheric pressure, the higher the altitude. The project is comprised of a microcontroller (MCU), an 84x84 pixel graphic LCD and a barometric pressure sensor.

The barometric pressure sensor used in the design is the MS560702BA03-50 from TE Connectivity Measurement Specialties. It consists of a piezo-resistive sensor and a sensor interface IC. Its main function is to convert the uncompensated analogue output voltage from the piezo-resistive pressure sensor to a 24-bit digital value, as well as providing a 24-bit digital value for the temperature of the sensor. It is optimized for altimeters and variometers with an altitude resolution of 20cm. The MS560702BA03-50 measures the atmospheric pressure on its location then converts it to a 24-bit value through its internal ADC. The sensor reading is then transmitted to the MCU through SPI. Then the MCU calculates the altitude by using the pressure reading. The calibration of an altimeter follows the equation z = cT log (Po /P), where c is a constant, T is the absolute temperature, P is the pressure at altitude z, and Po is the pressure at sea level. The calculated altitude is then displayed through an 84x84 pixel graphic LCD which is mostly found on old phones. The circuit is powered through a 3.3V battery.

The altimeter is used to aid navigation and is mostly used in skydiving, mountaineering and hiking applications. It is usually hand-held or in wrist-mount form for the ease of use. Altimeters can also be found in aircrafts such as planes and helicopters and others that needs altitude indication.