Barometer 2 Click is a digital barometer on a Click board™. Barometer 2 is equipped with the LPS35HW, an absolute piezoresistive pressure sensor with ceramic, water resistant package, manufactured using a proprietary technology. This sensor offers many benefits, including low power consumption, high resolution of the pressure data, embedded thermal compensation, FIFO buffer with several operating modes, temperature measurement, etc. The most distinctive feature of this sensor is its ability to measure the pressure within the wide range between 260 - 1260hPa, offering calibrated readings over I2C digital interface.
Barometer 2 Click is supported by a mikroSDK compliant library, which includes functions that simplify software development.
The pressure sensor is packed in ceramic, water-resistant housing, preventing water or humidity to damage the circuit. Additionally, it is protected from overpressure, allowing it to withstand pressure peaks up to 20x its measurement range. These features make Barometer 2 Click a perfect tool for the development of various pressure-based applications, especially when low power consumption is required: portable weather stations, IoT and other battery-operated pressure-related applications, wearables, and similar.
Barometer 2 Click features the LPS35HW, an absolute digital output barometer IC in water-resistant package, from STMicroelectronics. It can be used to measure absolute pressure values from 260 - 1260hPa. The sensor can be exposed up to 2MPa of pressure peaks, without causing any permanent damage. However, prolonged exposure to such high pressure can affect the reliability and accuracy of the sensor.
The LPS35HW IC comprises a piezoresistive MEMS and an ASIC. The MEMS consists of a suspended membrane manufactured using a proprietary technology, developed by ST. The piezoresistive elements on the membrane form a Wheatstone bridge. By applying a pressure, the balance of the bridge is disturbed, which causes a proportional voltage to appear on its output. The output of the Wheatstone bridge is then processed by the ASIC, which outputs conditioned and factory-calibrated data over the I2C interface, in 24-bit, two’s complement format.
Barometer 2 Click supports the I2C communication interface, allowing it to be used with a wide range of different MCUs. The peripheral I2C address can be configured by an SMD jumper, labeled as ADD SEL. An SMD jumper is used to set the least significant bit (LSB) of the I2C address. When set to 1, the 7-bit I2C peripheral address becomes 0b1011101x. If set to 0, the address becomes 0b1011100x. The last digit (x) is the R/W bit.
One of distinctive features of the LPS35HW is a highly configurable FIFO buffer, with 32 slots of 40-bit data, allowing to buffer both pressure and temperature readings. The FIFO buffer can be configured to work in one of several available modes, offering a great flexibility. Along with the extensive interrupt engine which can signal several FIFO-related events over a dedicated INT_DRDY pin, the FIFO buffer can be very useful for writing an optimized MCU firmware.
Besides FIFO-related events, the extensive interrupt engine of the LPS35HW IC can be configured to signal several other events over a dedicated INT_DRDY pin, including events when a programmable low or high threshold level is exceeded, and events when there is a data ready to be read from the output. The INT_DRDY pin of the LPS35HW IC is routed to the mikroBUS™ INT pin. Its active state (active LOW or active HIGH) is freely configurable.
Pressure data at the output is in 24-bit, two’s complement format. Thanks to the highly advanced ASIC, the output is already formatted in physical units, with minimum operations required from the host MCU. Since the sensitivity is 4096 LSB/hPa, the output result should be divided by 4096 in order to obtain the value in hPa units. Temperature data is in 16-bit two’s complement format, and it does not require any conversions. The sensitivity of the temperature sensor is 100 LSB/⁰C so the output result should be divided by 100 in order to obtain the value in ⁰C units. ASIC also offers some other processing functions such as the lowpass filtering of the output data, which helps reducing the inconsistencies due to sudden pressure changes.
This Click board™ uses both I2C, and it is designed to be operated only with 3.3V logic level. A proper logic voltage level conversion should be performed before the Click board™ is used with MCUs with logic levels of 5V.
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