Arduino library for Pololu LPS pressure sensor boards

Version: 3.1.0
Release date: 2019-05-11

www.pololu.com

Summary

This is a library for an Arduino-compatible controller that interfaces with ST LPS25H/B and LPS331AP pressure sensors on Pololu boards. The library makes it simple to read the raw pressure data from these boards:

• Pololu LPS25HB pressure/altitude sensor carrier
• Pololu LPS25H pressure/altitude sensor carrier (deprecated)
• Pololu LPS331AP pressure/altitude sensor carrier (deprecated)
• AltIMU-10 v5 (LSM6DS33, LIS3MDL, and LPS25H carrier)
• AltIMU-10 v4 (L3GD20H, LSM303D, and LPS25H carrier) (deprecated)
• AltIMU-10 v3 (L3GD20H, LSM303D, and LSM331AP carrier) (deprecated)
• AltIMU-10 (L3GD20, LSM303DLHC, and LSM331AP carrier) (discontinued)

The library also provides functions to help calculate altitude based on the measured pressure.

Getting started

Hardware

A LPS carrier can be purchased from Pololu's website. Before continuing, careful reading of the product page as well as the chip datasheet is recommended.

Make the following connections with wires between the Arduino and the LPS board:

5V Arduino boards

(including Arduino Uno, Leonardo, Mega; Pololu A-Star 32U4)

Arduino   LPS board
-------   ---------
     5V - VIN
    GND - GND
    SDA - SDA
    SCL - SCL

3.3V Arduino boards

(including Arduino Due)

Arduino   LPS board
-------   ---------
    3V3 - VIN
    GND - GND
    SDA - SDA
    SCL - SCL

Software

If you are using version 1.6.2 or later of the Arduino software (IDE), you can use the Library Manager to install this library:

1. In the Arduino IDE, open the "Sketch" menu, select "Include Library", then "Manage Libraries...".
2. Search for "LPS".
3. Click the LPS entry in the list.
4. Click "Install".

If this does not work, you can manually install the library:

1. Download the latest release archive from GitHub and decompress it.
2. Rename the folder "lps-arduino-xxxx" to "LPS".
3. Drag the "LPS" folder into the "libraries" directory inside your Arduino sketchbook directory. You can view your sketchbook location by opening the "File" menu and selecting "Preferences" in the Arduino IDE. If there is not already a "libraries" folder in that location, you should make the folder yourself.
4. After installing the library, restart the Arduino IDE.

Examples

Several example sketches are available that show how to use the library. You can access them from the Arduino IDE by opening the "File" menu, selecting "Examples", and then selecting "LPS". If you cannot find these examples, the library was probably installed incorrectly and you should retry the installation instructions above.

SerialMetric

This program continuously takes pressure and temperature readings from the sensor and calculates an altitude from the pressure. It shows the data in metric units: pressure in millibars (mbar) (which are equivalent to hectopascals (hPa)), altitude in meters, and temperature in degrees Celsius. The program's output is sent over the serial interface, and you can display it with the Arduino Serial Monitor.

Example output:

p: 931.93 mbar	a: 700.02 m	t: 29.92 deg C
p: 931.85 mbar	a: 700.73 m	t: 29.92 deg C
p: 931.75 mbar	a: 701.68 m	t: 29.89 deg C

SerialUS

This program is the same as SerialMetric, except that it shows the data in United States customary units: pressure in inches of mercury (inHg), altitude in feet, and temperature in degrees Fahrenheit.

Example output:

p: 27.52 inHg	a: 2296.55 ft	t: 83.19 deg F
p: 27.52 inHg	a: 2295.50 ft	t: 83.18 deg F
p: 27.52 inHg	a: 2296.42 ft	t: 83.17 deg F

OPCHelper

This program helps to determine what the RPDS registers should be after you have soldered it. It helps to have some idea what the values should be instead of hunting and pecking with trial and error. This may help for you to zero in on a value much more quickly.

Example output:

Pololu LPS OPC Helper
Your local pressure:    1016.40 mbar, which is 4163174 int32_t
Your local altitude:    419.70 m
According to the current device state, your local QFF should be:
<some float value>
Sensor raw pressure:     4153535 int32_t
Sensor millibars:        1014.05 mbar
Current RPDS_L:          1010001 binary
Current RPDS_H:          0 binary

Library reference

• bool init(deviceType device, byte sa0)
  Initializes the library with the device being used (LPS::device_331AP, LPS::device_25H, or LPS::device_auto) and the state of the SA0 pin (LPS::sa0_low, LPS::sa0_high, or LPS::sa0_auto; LOW or HIGH also work), which determines the least significant bit of the sensor's address. Both of these arguments are optional; if they are not specified, the library will try to automatically detect the device and address. The return value is a boolean indicating whether a device was successfully detected.
• deviceType getDeviceType(void)
  Returns the device type detected by init().
• byte getAddress(void)
  Returns the address detected by init().
• void enableDefault(void)
  Turns on the pressure sensor in a default configuration that gives continuous output at 12.5 Hz.
• void enable1Hz(void)
  Turns on the pressure sensor in a default configuration that gives continuous output at 1Hz.
• void enableFifo(fifoMode mode)
  Enables the hardware FIFO for the given mode.
• void writeReg(int reg, byte value)
  Writes a pressure sensor register with the given value. Register addresses are defined by the regAddr enumeration type in LPS.h. Example use: ps.writeReg(LPS::CTRL_REG1, 0xE0);
• byte readReg(int reg)
  Reads a pressure sensor register and returns the value read.
• float readPressureMillibars(void)
  Returns a pressure reading from the sensor in units of millibars (mbar)/hectopascals (hPa).
• float readPressureInchesHg(void)
  Returns a pressure reading from the sensor in units of inches of mercury (inHg).
• long readPressureRaw(void)
  Returns a raw 24-bit pressure reading from the sensor.
• float readTemperatureC(void)
  Returns a temperature reading from the sensor in units of degrees Celsius.
• float readTemperatureF(void)
  Returns a temperature reading from the sensor in units of degrees Fahrenheit.
• int readTemperatureRaw(void)
  Returns a raw 16-bit temperature reading from the sensor.
• float pressureToAltitudeMeters(float pressure_mbar, float altimeter_setting_mbar)
  Converts a pressure in mbar to an altitude in meters, using the 1976 U.S. Standard Atmosphere model (note that this formula only applies up to an altitude of 11 km, or about 36000 ft). If the optional altimeter_setting_mbar argument is given, specifying an "altimeter setting" or "QNH" (barometric pressure adjusted to sea level, often used in aviation and obtained from a local weather monitoring station), this function returns an indicated altitude compensated for the actual regional pressure. Otherwise, it returns a pressure altitude above the standard pressure level of 1013.25 mbar (29.9213 inHg).
• float pressureToAltitudeFeet(float pressure_inHg, float altimeter_setting_inHg)
  Converts a pressure in inHg to an altitude in feet. See the preceding description of pressureToAltitudeMeters() for details.
• float pressureToAltitude(float pressure, float altimeter_setting, bool metric)
  Converts a pressure to an altitude. A generic version of the above two functions. Metric pressure and altimeter are expected to be mbars and meters. Otherwise inHg and feet, respectively.
• float altitudeToQFF(float altitude_meters, float tempC, bool return_mbars)
  Useful for reporting sea level pressure assuming you know the altitude of your sensor. Once your device is calibrated, you can use this to report local pressure.
• int32_t opcHelper(float my_local_qff_mbar, float my_local_altitude_meters)
  Useful for calibrating the device so you can assign RPDS registers to correct for changes to pressure value reporting from the device due to soldering.

Version history

• 3.1.0 (2019-05-07): Added helper functions and variables
  • Enums for FIFO modes
  • Enable FIFO function
  • Altitude to sea level pressure function
  • OPC helper to determine post-solder offsets
• 3.0.0 (2016-08-17): Updated library to work with the Arduino Library Manager.
• 2.0.0 (2014-06-03): Major rewrite. List of significant changes:
  • Renamed library to LPS.
  • Added support for LPS25H and automatic detection of device type.
  • Library constants converted to enums.
• 1.0.1 (2014-01-08): Changed raw output byte combination logic to work properly on 32-bit microcontrollers and be more portable.
• 1.0.0 (2013-03-22): Original release of LPS331 library.

For a rigorously complete implementation of the LPS25HB, ST's github version at https://github.com/stm32duino/LPS25HB provides interfaces for almost every function on the chip.