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  • MPL115A2 Digital Barometer

  • Created: Apr 23, 2015

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Summary

The digital barometer is a scientific instrument that measures atmospheric pressure. It effectively measures subtle pressure changes caused by weather such as this evaluation board that specifically uses the Freescale's MPL115A which digital I2C output targeting low cost commercial applications. The device employs a MEMS PRT pressure sensor with a conditioning IC to provide accurate pressure data. The sensor output is accurate to ±1kPa over the 50kPa to 115kPa pressure range. An integrated ADC provides digitized temperature and pressure sensor outputs via an I2C or SPI bus.


The evaluation board is comprised with sensor parts, pull-up resistors and decoupling capacitors that is soldered onboard. Calibration data is housed in on-board ROM. This data is used typically by a host microcontroller to apply a compensation algorithm to the raw Analog-to-Digital Converter (ADC) data from the pressure sensor and may be accessed at any time. The calibration data is stored as a series of coefficients that are applied to the raw data to compensate for temperature and pressure variation in the raw output. The MPL115A interfaces to a host (or system) microcontroller in the user's application where all communications are via I2C. During initial power-up, all circuit elements are active and I2C port pins are high impedance and associated registers are cleared. The user then typically accesses the part and reads the coefficient data. The main circuits within the slave device are disabled during read activity. The coefficients are usually stored in the host microcontroller local memory but can be reread at any time. The data conversion is the first step that is performed each time a new pressure reading is required which is initiated by the host sending the CONVERT command. The main system circuits are activated (wake) in response to the command and after the conversion completes, the result is placed into the pressure and temperature ADC output registers. After the conversion has been given sufficient time to complete, the host microcontroller reads the result from the ADC output registers and calculates the compensated pressure, a barometric/atmospheric pressure value which is compensated for changes in temperature and pressure sensor linearity. From this step the host controller may either wait or then return to the data conversion step to obtain the next pressure reading or it may go to the shutdown step.


The MPL115A is an absolute pressure sensor with digital output for low cost applications. A miniature 5 x 3 x 1.2 mm LGA package ideally suits it for portable electronics and space constrained applications. With its wide operating temperature range from -40°C to +105°C definitely fits demanding environmental requirements. Digital barometer has various applications for use in weather stations, air control systems, industrial equipment and health monitoring.

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