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LIS3DH 3-Axis Accelerometer

Build Status

The LIS3DH is a three-axis MEMS accelerometer. The LIS3DH application note can be found here. This sensor has extensive functionality and this class has not yet implemented all of it.

This library also supports the LIS2DH12, another widely used three-axis MEMS accelerometer and which can be found on Electric Imp’s impExplorer™ Kit.

The LIS3DH can interface over I²C or SPI. This class addresses only I²C for the time being.

To add this library to your project, add #require "LIS3DH.device.lib.nut:2.0.1" to the top of your device code

Class Usage

Constructor: LIS3DH(i2cBus[, i2cAddress])

The class’ constructor takes one required parameter (a configured imp I²C bus) and an optional parameter (the I²C address of the accelerometer). The I²C address must be the address of your sensor or an I²C error will be thrown.

Parameter Type Default Description
i2cBus hardware.i2c N/A A pre-configured I²C bus
i2cAddress byte 0x30 The I²C address of the accelerometer
i2c <- hardware.i2c89;
i2c.configure(CLOCK_SPEED_400_KHZ);

// Use a non-default I2C address (SA0 pulled high)
accel <- LIS3DH(i2c, 0x32);

Class Methods

reset()

The reset() method resets all control and interrupt registers to datasheet default values. This method need only be called to restore registers to thesedefault conditions.

accel.reset();

setDataRate(rateHz)

The setDataRate() method sets the Output Data Rate (ODR) of the accelerometer in Hertz. Supported datarates are 0 (Shutdown), 1, 10, 25, 50, 100, 200, 400, 1250 (Normal Mode only), 1600 (Low-Power Mode only) and 5000 (Low-Power Mode only). The requested data rate will be rounded up to the closest supported rate and the actual data rate will be returned.

The default data rate is 0 (Shutdown). To take a reading with getAccel() you must set a data rate greater than 0.

local rate = accel.setDataRate(90);
server.log(format("Accelerometer running at %dHz", rate));
// Displays 'Accelerometer running at 100Hz'

setMode(mode)

The setMode() method sets the accelerometer into low power, normal or high resolution mode. The method takes one of three mode constants: LIS3DH_MODE_NORMAL, LIS3DH_MODE_LOW_POWER or LIS3DH_MODE_HIGH_RESOLUTION. The default mode is LIS3DH_MODE_NORMAL.

accel.setMode(LIS3DH_MODE_HIGH_RESOLUTION);

enableADC(state)

The enableADC() method enables the three ADC lines available to the LIS3DH (the LIS2DH does not have these auxiliary lines available). Its input ranges from approximately 0.8-1.6V. By default, the ADC is disabled.

accel.enableADC(true);

readADC(line)

The readADC() method returns a reading from approximately 0.8-1.6V from the specified ADC line. The required line, one of three, is set by providing one the following constants: LIS3DH_ADC1, LIS3DH_ADC2 or LIS3DH_ADC3. The ADC must first be enabled by calling enableADC(true).

accel.enableADC(true);
local reading = accel.readADC(LIS3DH_ADC1);

enable([state])

The enable() method enables or disables all three axes on the accelerometer. The method takes an optional boolean parameter, state. By default state is set to true and the accelerometer is enabled. When state is false, the accelerometer will be disabled.

function goToSleep() {
    imp.onidle(function() {
        // Set data rate to 0 and disable the accelerometer to save power
        accel.setDataRate(0);
        accel.enable(false);

        // Sleep for 1 hour
        server.sleepfor(3600);
    });
}

getAccel([callback])

The getAccel() method reads the latest measurement from the accelerometer. The method takes an optional callback for asynchronous operation — it will block otherwise. The callback should take one parameter: a results table (see below). If the callback is null or omitted, the method will return the results table:

{ "x": <xData>,
  "y": <yData>,
  "z": <zData> }

Synchronous Example

accel.setDataRate(100);
local val = accel.getAccel();
server.log(format("Acceleration (G): (%0.2f, %0.2f, %0.2f)", val.x, val.y, val.z));

Asynchronous Example

accel.setDataRate(100);
accel.getAccel(function(val) {
    server.log(format("Acceleration (G): (%0.2f, %0.2f, %0.2f)", val.x, val.y, val.z));
});

setRange(range)

The setRange() method sets the measurement range of the sensor in Gs. Supported ranges are ± 2, 4, 8 and 16G. The data rate will be rounded up to the closest supported range and the actual range will be returned. The default measurement range is ±2G.

// Set sensor range to +/- 8G
local range = accel.setRange(8);
server.log(format("Range set to +/- %dG", range));

getRange()

The getRange() method returns the current measurement range of the sensor in Gs.

server.log(format("Current Sensor Range is +/- %dG", accel.getRange()));

configureFifoInterrupt(state[, fifomode][, watermark])

This method configures an interrupt when the FIFO buffer reaches the set watermark:

Parameter Type Default Value Description
state Boolean N/A true to enable, false to disable
fifomode bitfield LIS3DH_FIFO_STREAM_MODE See table below
watermark Integer 28 Number of buffer slots filled to generate
interrupt (buffer has 32 slots)

This example sets the FIFO buffer to Stream Mode and reads the data from the buffer whenever the watermark is reached:

// Function to read from FIFO buffer
function readBuffer() {
    if (wakePin.read() == 0) return;

    // Read buffer
    local stats = accel.getFifoStats();
    for (local i = 0 ; i < stats.unread ; i++) {
        local data = accel.getAccel();
        server.log(format("Accel (x,y,z): [%d, %d, %d]", data.x, data.y, data.z));
    }

    // Check if we are now over-run
    local stats = accel.getFifoStats();
    if (stats.overrun) {
        server.error("Accelerometer buffer over-run");

        // Set FIFO mode to bypass to clear the buffer and then return to stream mode
        accel.configureFifoInterrupt(true, LIS3DH_FIFO_BYPASS_MODE);
        accel.configureFifoInterrupt(true, LIS3DH_FIFO_STREAM_MODE, 30);
    }

}

i2c  <- hardware.i2cAB;
i2c.configure(CLOCK_SPEED_400_KHZ);
accel <- LIS3DH(i2c);

// Configure interrupt pin
wakePin <- hardware.pinW;
wakePin.configure(DIGITAL_IN_PULLDOWN, readBuffer);

// Configure accelerometer
accel.init();
accel.setDataRate(100);

// Configure the FIFO buffer in Stream Mode and set interrupt generator
// to generate an interrupt when there are 30 entries in the buffer
accel.configureFifoInterrupt(true, LIS3DH_FIFO_STREAM_MODE, 30);

FIFO modes

Mode Description
LIS3DH_FIFO_BYPASS_MODE Disables the FIFO buffer (only the first address is used for each channel)
LIS3DH_FIFO_FIFO_MODE When full, the FIFO buffer stops collecting data from the input channels
LIS3DH_FIFO_STREAM_MODE When full, the FIFO buffer discards the older data as the new arrive
LIS3DH_FIFO_STREAM_TO_FIFO_MODE When full, the FIFO buffer discards the older data as the new arrive.
Once trigger event occurs, the FIFO buffer starts operating in FIFO mode

configureInertialInterrupt(enable[, threshold][, duration][, options])

This method configures the inertial interrupt generator.

Parameter Type Default Value Description
enable Boolean N/A true to enable, false to disable
threshold Float 2.0 Inertial interrupts threshold in Gs
duration Integer 5 Number of samples exceeding threshold
required to generate interrupt
options bitfield LIS3DH_X_HIGH | LIS3DH_Y_HIGH | LIS3DH_Z_HIGH See table below
// Configure the Inertial interrupt generator to generate an interrupt
// when acceleration on all three exceeds 1G.
accel.configureInertialInterrupt(true, 1.0, 10, LIS3DH_X_LOW | LIS3DH_Y_LOW | LIS3DH_Z_LOW | LIS3DH_AOI)

The default configuration for the Intertial Interrupt generator is to generate an interrupt when the acceleration on any axis exceeds 2G. This behavior can be changed by OR-ing together any of the following flags:

Flag Description
LIS3DH_X_LOW Generates an interrupt when the x-axis acceleration goes below the threshold
LIS3DH_X_HIGH Generates an interrupt when the x-axis acceleration goes above the threshold
LIS3DH_Y_LOW Generates an interrupt when the y-axis acceleration goes below the threshold
YLIS3DH__HIGH Generates an interrupt when the y-axis acceleration goes above the threshold
LIS3DH_Z_LOW Generates an interrupt when the z-axis acceleration goes below the threshold
LIS3DH_Z_HIGH Generates an interrupt when the z-axis acceleration goes above the threshold
LIS3DH_AOI Sets the AOI flag (see ‘Inertial Interrupt Modes’ below)
LIS3DH_SIX_D Sets the 6D flag (see ‘Inertial Interrupt Modes’ below)

Inertial Interrupt Modes

The following is taken from the from LIS3DH Datasheet (section 8.21):

AOI 6D Interrupt Mode
0 0 OR combination of interrupt events
0 1 6-direction movement recognition
1 0 AND combination of events
1 1 6-direction position recognition

Movement Recognition (01) An interrupt is generate when orientation move from unknown zone to known zone. The interrupt signal stay for a duration ODR.

Direction Recognition (11) An interrupt is generate when orientation is inside a known zone. The interrupt signal stay until orientation is inside the zone.

configureFreeFallInterrupt(enable[, threshold][, duration])

This method configures the intertial interrupt generator to generate interrupts when the device is in free fall (acceleration on all axis approaches 0). The default threshold is 0.5G. The default duration is five samples.

accel.configureFreeFallInterrupt(true);

Note This method will overwrite any settings configured with the configureInertialInterrupt().

configureClickInterrupt(enable[, clickType][, threshold][, timeLimit][, latency][, window])

This method configures the click interrupt generator.

Parameter Type Default Value Description
enable Boolean N/A true to enable, false to disable
clickType Constant LIS3DH_SINGLE_CLICK LIS3DH_SINGLE_CLICK or LIS3DH_DOUBLE_CLICK
threshold Float 1.1 Threshold that must be exceeded to be considered a click
timeLimit Float 5 Max time in milliseconds the acceleration can spend above the threshold to be considered a click
latency Float 10 Min time in milliseconds between the end of one click event and the start of another to be considered a LIS3DH_DOUBLE_CLICK
window Float 50 Max time in milliseconds between the start of one click event and end of another to be considered a LIS3DH_DOUBLE_CLICK

Single Click Example

// Configure a single click interrupt
accel.configureClickInterrupt(true, LIS3DH_SINGLE_CLICK);

Double Click Example

// configure a double click interrupt
accel.configureClickInterrupt(true, LIS3DH_DOUBLE_CLICK);

configureDataReadyInterrupt(enable)

This method enables (enable is true) or disables (enable is false) data-ready interrupts on the sensor’s INT1 line. The data-ready signal rises to 1 when a new set of acceleration data has been generated and it is available for reading. The interrupt is reset when the higher part of the data of all the enabled channels has been read.

accel.setDataRate(1); // 1Hz
accel.configureDataReadyInterrupt(true);

configureInterruptLatching(enable)

This method enables (enable is true) or disables (enable is false) interrupt latching. If interrupt latching is enabled, the interrupt signal will remain asserted until the interrupt source register is read by calling getInterruptTable(). If latching is disabled, the interrupt signal will remain asserted as long as the interrupt-generating condition persists.

Interrupt latching is disabled by default.

For an example, see the sample code under getInterruptTable(), below.

getInterruptTable()

The getInterruptTable() method reads the LIS3DH’s INT1_SRC and CLICK_SRC registers, and returns the result as a table with the following keys:

Key Type Description
int1 Bool true if INT1 created the interrupt
xLow Bool true if a xLow condition is present
yLow Bool true if a yLow condition is present
zLow Bool true if a zLow condition is present
xHigh Bool true if a xHigh condition is present
yHigh Bool true if a yHigh condition is present
zHigh Bool true if a zHigh condition is present
click Bool true if any click created the interrupt
singleClick Bool true if a single click created the interrupt
doubleClick Bool true if a double click created the interrupt

In the following example we setup an interrupt for double-click detection:

function interruptHandler() {
    if (int.read() == 0) return;

    // Get + clear the interrupt + clear
    local data = accel.getInterruptTable();

    // Check what kind of interrupt it was
    if (data.doubleClick) server.log("Double Click");
}

i2c <- hardware.i2c89;
i2c.configure(CLOCK_SPEED_400_KHZ);
accel <- LIS3DH(i2c, 0x32);

int <- hardware.pinB;
int.configure(DIGITAL_IN, interruptHandler);

// Configure accelerometer
accel.setDataRate(100);

// Set up a double-click interrupt
accel.configureClickInterrupt(true, LIS3DH_DOUBLE_CLICK);

In the following example we setup an interrupt for free-fall detection:

function sensorSetup() {
    // Configure accelerometer
    accel.setDataRate(100);
    accel.configureInterruptLatching(true);

    // Setup a free fall interrupt
    accel.configureFreeFallInterrupt(true);
}

// Put imp to Sleep
function sleep(timer) {
    server.log("going to sleep for " + timer + " sec");
    if (server.isconnected()) {
        imp.onidle(function() { 
           server.sleepfor(timer); 
        });
    } else {
        imp.deepsleepfor(timer);
    }
}

// Take reading
function takeReading() {
    accel.getAccel(function(result) {
        if ("err" in result) {
            // Check for error
            server.log(result.err);
        } else {
            // Add timestamp to result table
            result.ts <- time();
            // Log reading
            foreach(k, v in result) {
                server.log(k + ": " + v);
            }
        }
    });
}

function interruptHandler() {
    if (int.read() == 0) return;

    // Get + clear the interrupt + clear
    local data = accel.getInterruptTable();

    // Check what kind of interrupt it was
    if (data.int1) server.log("Free Fall");
    
    sleep(30);
}

i2c <- hardware.i2c89;
i2c.configure(CLOCK_SPEED_400_KHZ);
accel <- LIS3DH(i2c, 0x32);

int <- hardware.pinB;
wake <- hardware.pin1;

int.configure(DIGITAL_IN);
wake.configure(DIGITAL_IN_WAKEUP);

// Handle WakeUp
switch(hardware.wakereason()) {
    case WAKEREASON_TIMER:
        server.log("WOKE UP B/C TIMER EXPIRED");
        takeReading();
        imp.wakeup(2, function() { sleep(30); })
        break;
    case WAKEREASON_PIN:
        server.log("WOKE UP B/C PIN HIGH");
        interruptHandler();
        break;
    default:
        server.log("WOKE UP B/C RESTARTED DEVICE, LOADED NEW CODE, ETC");
        sensorSetup();
        takeReading();
        imp.wakeup(2, function() { sleep(30); })
}

getFifoStats()

This method returns information about the state of the FIFO buffer in a Squirrel table with the following keys:

Key Type Description
watermark Boolean true if watermark has been set
overrun Boolean true if data has been overwritten without being read
empty Boolean true if buffer is empty
unread Integer Number of unread slots in buffer

configureHighPassFilter(filters[, cutoff][, mode])

This method configures the high-pass filter.

Parameter Type Default Value Description
filters Constant N/A Select the filter(s) to enable/disable by OR-ing together any of the constants found in the filters table below
cutoff Constant LIS3DH_HPF_CUTOFF1 See high-pass filter cut-off frequency table below
mode Constant LIS3DH_HPF_DEFAULT_MODE See modes table below

Filters

Filter Constant Description
LIS3DH_HPF_AOI_INT1 High-pass filter enabled for AOI function on interrupt 1
LIS3DH_HPF_AOI_INT2 High-pass filter enabled for AOI function on interrupt 2
LIS3DH_HPF_CLICK High-pass filter enabled for CLICK function
LIS3DH_HPF_FDS Filtered data selection. Enables data from internal filter sent to output register and FIFO
LIS3DH_HPF_DISABLED Disables all filters

High-pass Filter Cut-off Frequencies

Cut-off Constant f@1Hz f@10Hz f@25Hz f@50Hz f@100Hz f@200Hz f@400Hz f@1600Hz f@5000Hz
LIS3DH_HPF_CUTOFF1 0.02 0.2 0.5 1 2 4 8 32 100
LIS3DH_HPF_CUTOFF2 0.008 0.08 0.2 0.5 1 2 4 16 50
LIS3DH_HPF_CUTOFF3 0.004 0.04 0.1 0.2 0.5 1 2 8 25
LIS3DH_HPF_CUTOFF4 0.002 0.02 0.05 0.1 0.2 0.5 1 4 12

Modes

Mode Constant Description
LIS3DH_HPF_DEFAULT_MODE Normal mode (reset reading HP_RESET_FILTER)
LIS3DH_HPF_REFERENCE_SIGNAL Reference signal for filtering
LIS3DH_HPF_NORMAL_MODE Normal mode
LIS3DH_HPF_AUTORESET_ON_INTERRUPT Autoreset on interrupt event

Example

// Enable high-pass filter on click and intertial interrupt 1 with auto reset on interrupt event
accel.configureHighPassFilter(LIS3DH_HPF_AOI_INT1 | LIS3DH_HPF_CLICK, null, LIS3DH_HPF_AUTORESET_ON_INTERRUPT);

// Disable high pass filter
accel.configureHighPassFilter(LIS3DH_HPF_DISABLED);

getDeviceId()

Returns the one-byte device ID of the sensor (from the WHO_AM_I register). The getDeviceId() method is a simple way to test if your LIS3DH sensor is correctly connected.

server.log(format("Device ID: 0x%02X", accel.getDeviceId()));

License

The LIS3DH class is licensed under MIT License.

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Driver library for the LIS3DH MEMS Accelerometer

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