Pressure Altitude sensor
This board is a compact (0.4″ × 0.9″) carrier for ST’s LPS331AP MEMS absolute pressure sensor, or barometer; we therefore recommend careful reading of the LPS331AP datasheet (453k pdf) before using this product. The LPS331 is a great IC, but its small, leadless, LGA package makes it difficult for the typical student or hobbyist to use. It also operates at voltages below 3.6 V, which can make interfacing difficult for microcontrollers operating at 5 V. This carrier board addresses these issues by incorporating additional electronics, including a 3.3 V voltage regulator and level-shifting circuits, while keeping the overall size as compact as possible. The board ships fully populated with its SMD components, including the LPS331AP, as shown in the product picture. The LPS331 features embedded temperature compensation and has many configurable options, including selectable resolutions, a choice of output data rates, and two programmable external interrupt signals. Its pressure output has an absolute accuracy as low as ±2 mbar (0.2 kPa), with RMS noise of 0.02 mbar (0.002 kPa) in the highest-resolution mode.
Pressure and temperature sensor data are available through a digital interface, which can be configured to operate in either I²C or SPI mode, and can be used for altimetry. (See the Sample Code section below for an Arduino library that can be used to turn this sensor into an altimeter). The carrier board includes a low-dropout linear voltage regulator that provides the 3.3 V required by the LPS331, which allows the sensor to be powered from a 2.5 V to 5.5 V supply. The regulator output is available on the VDD pin and can supply almost 150 mA to external devices. The breakout board also includes a circuit that shifts the I²C/SPI clock and data in lines to the same logic voltage level as the supplied VIN, making it simple to interface the board with 5 V systems, and the board’s 0.1″ pin spacing makes it easy to use with standard solderless breadboards and 0.1″ perfboards. For sensor fusion applications, AltIMU-10 inertial measurement unit combines the LPS331AP with an L3GD20 3-axis gyro and an LSM303DLHC 3-axis accelerometer and 3-axis magnetometer on a single board, providing ten independent readings that can be used to calculate an absolute orientation and altitude.