This board is a compact (0.4″ × 0.8″) carrier for ST’s LPS25H MEMS absolute pressure sensor, or barometer; we therefore recommend careful reading of the LPS25H datasheet (1MB pdf) before using this product. The LPS25H 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 LPS25H, as shown in the product picture.
Compared to the earlier LPS331AP, the LPS25H features improved accuracy and reduced noise in the output. The addition of a built-in FIFO (First In, First Out) buffer allows the sensor to store pressure readings for burst transmission, reducing overall power consumption by allowing the host processor to sleep longer between data requests. Alternatively, the FIFO can be configured to perform a running average of pressure readings to further decrease the output noise.
This LPS25H carrier board is pin-compatible with our LPS331AP carrier, but due to the removal of one of the interrupt pins on the LPS25H, the position of the mounting hole has changed relative to the remaining pins. The two sensors use the same I²C addresses, but some of their configuration register fields are different, so code written to interface with an LPS331 might need to be modified to work with an LPS25H.
The LPS25H features embedded temperature compensation and has many configurable options, including selectable resolutions, a choice of output data rates, several FIFO operating modes, and a programmable external interrupt signal. Its pressure output has an absolute pressure accuracy over temperature as low as ±0.2 mbar (0.02 kPa), with RMS noise of 0.01 mbar (0.001 kPa) in the highest-resolution mode with embedded filtering enabled. 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 LPS25H, 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.