LPS25H

The LPS25H is a MEMS absolute pressure sensor. This sensor features a large functional range (260-1260hPa) and internal averaging for improved precision.

The LPS25H can interface over I²C or SPI. This class addresses only I²C for the time being.

You can view the library’s source code on GitHub. Click here to see information on other versions of this library.

To add this library to your project, add #require "LPS25H.class.nut:2.0.1" to the top of your device code

Hardware

To use the LPS25H, connect its I²C interface to any of your imp module’s I²C buses. To learn which pins provide I²C functionality, see the imp pin mux in the Electric Imp Dev Center.

The LPS25H interrupt pin behavior may be configured through this class, but the corresponding imp pin and associated callback are not configured or managed through this class. To use the interrupt pin:

• Connect the LPS25H’s INT1 pin to an imp GPIO pin
• Configure the imp pin connected to INT1 as a DIGITAL_IN with your desired callback function
• Use the methods in this class to configure the interrupt behavior as required

Class Usage

Constructor: LPS25H(impI2cBus[, i2cAddress])

The constructor takes two arguments to instantiate the class: a pre-configured I²C bus and the sensor’s I²C address in 8-bit form. The I²C address is optional and defaults to 0xB8.

#require "LPS25H.class.nut:2.0.1"

// Non-default 8-bit I2C Address for LPS25H (SA0 pulled high)
const LPS25H_ADDR = 0xBA;

hardware.i2c89.configure(CLOCK_SPEED_400_KHZ);
pressureSensor <- LPS25H(hardware.i2c89, LPS25H_ADDR);

Reset

The LPS25H is not automatically reset when constructed so that Electric Imp applications can use the device through sleep/wake cycles without it losing state. To reset the device to a known state, call the softReset() method:

hardware.i2c89.configure(CLOCK_SPEED_400_KHZ);
pressureSensor <- LPS25H(hardware.i2c89);
pressureSensor.softReset();

After a reset, the LPS25H will be disabled. Call enable() to use the device.

Class Methods

enable(state)

Enable (state = true) or disable (state = false) the LPS25H. The device must be enabled before attempting to read the pressure or temperature. If the device is disabled and a reading is taken it will return stale data.

pressureSensor.enable(true);    // Enable the sensor

read([callback])

The read() method returns a pressure reading in hPa. The reading result is in the form of a table with the field pressure. If an error occurs during the reading the pressure field will be null, and the reading table will contain an additional field, err, with a description of the error.

If a callback parameter is provided, the reading executes asynchronously, and the results table will be passed to the supplied function as the only parameter. If no callback is provided, the method blocks until the reading has been taken and then returns the results table.

Asynchronous example

pressureSensor.read(function(result) {
    if ("err" in result) {
        server.error("An Error Occurred: " + result.err);
    } else {
        server.log(format("Current Pressure: %0.2f hPa", result.pressure));
    }
});

Synchronous example

function hpaToHg(hpa) {
    return (1.0 * hpa) / 33.8638866667;
}

local result = pressureSensor.read();

if ("err" in result) {
    server.error("An Error Occurred: " + result.err);
} else {
    server.log(format("Current Pressure: %0.2f in. Hg", hpaToHg(result.pressure));
}

getTemp()

Returns the temperature in degrees Celsius.

server.log("Current Temperature: " + pressure.getTemp() + "C");

setReferencePressure(pressure)

Set the reference pressure for differential pressure measurements and interrupts (see configureInterrupt). Reference Pressure is in hectopascals (hPa). Negative pressures are supported. Reference Pressure range is ± 2046hPa.

server.log("Internal Reference Pressure Offset = " + pressure.getReferencePressure());

getReferencePressure()

Get the reference pressure for differential pressure measurements and interrupts (see configureInterrupt). Reference Pressure is in hectopascals (hPa).

server.log("Internal Reference Pressure Offset = " + pressure.getReferencePressure());

setDataRate(dataRate)

Sets the output data rate (ODR) of the pressure sensor in Hz. The nearest supported data rate less than or equal to the requested rate will be used and returned. Supported data rates are 0 (one shot configuration), 1, 7, 12.5 and 25Hz. The default value is 0Hz.

local dataRate = pressureSensor.setDataRate(7);
server.log(dataRate);

getDataRate()

Returns the output data rate (ODR) of the pressure sensor in Hz.

local dataRate = pressureSensor.getDataRate();
server.log(dataRate);

configureInterrupt(enable[, threshold][, options])

This method configures the interrupt pin driver, threshold, and sources. The device starts with this disabled by default.

Parameters

Parameter	Type	Default	Description
enable	boolean	N/A	Set true to enable the interrupt pin.
threshold	Integer	null	Interrupts are generated on differential pressure events; a high differential pressure interrupt occurs if (Absolute Pressure - Reference Pressure) > Threshold; a low differential pressure interrupt occurs if (Absolute Pressure - Reference Pressure) < (-1.0 * Threshold). The threshold is expressed in hectopascals (hPa).
options	Bitfield	0x00	Configuration options combined with the bitwise OR operator. See the ‘Options’ table below.

Options

Option Constant	Description
INT_ACTIVELOW	Interrupt pin is active-high by default. Use to set interrupt to active-low.
INT_OPENDRAIN	Interrupt pin driver push-pull by default.Use to set interrupt to open-drain.
INT_LATCH	Interrupt latching mode is disabled by default. Use to enable interrupt latching mode. To clear a latched interrupt pin call getInterruptSrc()
INT_LOW_PRESSURE	Interrupt is disabled by default. Use to enable interrupt when pressure below threshold
INT_HIGH_PRESSURE	Interrupt is disabled by default. Use to enable interrupt when pressure above threshold

// Enable interrupt, configure as push-pull, active-high, latched. Fire interrupt if (absolute pressure - reference pressure) > 10 hPa
pressureSensor.configureInterrupt(true, 10, LPS25H.INT_LATCH | LPS25H.INT_HIGH_PRESSURE);

// Enable interrupt, configure as open-drain, active-low, latched. Fire interrupt if (absolute pressure - reference pressure) < -20 hPa
pressureSensor.configureInterrupt(true, 20, LPS25H.INT_ACTIVELOW | LPS25H.INT_OPENDRAIN | LPS25H.INT_LATCH | LPS25H.INT_LOW_PRESSURE);

getInterruptSrc()

Determine what caused an interrupt, and clear latched interrupt. This method returns a table with three keys to provide information about which interrupts are active.

key	Description
int_active	true if an interrupt is currently active or latched
high_pressure	true if the active or latched interrupt was due to a high pressure event
low_pressure	true if the active or latched interrupt was due to a low pressure event

// Check the interrupt source and clear the latched interrupt
local intSrc = pressureSensor.getInterruptSrc();
if (intSrc.int_active) {
    // interrupt is active
    if (intSrc.high_pressure) server.log("High Pressure Interrupt Occurred");
    if (intSrc.low_pressure) server.log("Low Pressure Interrupt Occurred");
} else {
    server.log("No Interrupts Active");
}

setPressNpts(numberOfReadings)

Set the number of readings taken and then internally averaged to produce a pressure result. The value provided will be rounded up to the nearest valid value: 8, 32, 128 or 512. The actual value used is returned.

// Fastest readings, lowest precision
pressureSensor.setPressNpts(8);

// Slowest readings, highest precision
pressureSensor.setPressNpts(512);

// Rounding and checking result
local actualNpts = pressureSensor.setPressNpts(30);
// prints "Actual Pressure Npts = 32"
server.log("Actual Pressure Npts = " + actualNpts);

setTempNpts(numberOfReadings)

Set the number of readings taken and internally averaged to produce a temperature result. The value provided will be rounded up to the nearest valid value: 8, 16, 32 or 64. The actual value used is returned.

// Fastest readings, lowest precision
pressureSensor.setTempNpts(8);

// Slowest readings, highest precision
pressureSensor.setTempNpts(64);

softReset()

Reset the LPS25H from software. Device will come up disabled.

pressureSensor.softReset();

getDeviceID()

Returns the value of the device ID register, 0xBD.

Release History

The Electric Imp Dev Center documents the latest version of the library. For past versions, please see the Electric Imp public GitHub repos listed below.

Version	Source Code	Notes
1.0.0	GitHub	Initial release
2.0.0	GitHub	Major update — check your code
2.0.1	GitHub	Minor code changes

License

The LPS25H library is licensed under the MIT License.