Ambient Light Sensor

Light sensors measure illuminance, which can be used to measure more than the brightness of a light source.

MetaWear RPro and Cpro, and MetaDetector board come with a Lite-On LTR-329ALS ambient light sensor that can measure light from 0.01 lux to 64k lux.

Functions interacting with the light sensor are defined in the ambientlight_ltr329.h header file.

Configuration

The LTR329 sensor has 3 configurable parameters:

Parameter	Description
Gain	Controls data range and resolution
Integration Time	Measurement time for each cycle
Measurement Rate	How frequently to update illuminance data

Possible values for each of these parameters are defined in their respective enums. After configuring the API with the desired settings, call mbl_mw_als_ltr329_write_config. to write the settings to the sensor.

#include "metawear/sensor/ambientlight_ltr329.h"

void configure_als(MblMwMetaWearBoard* board) {
    // Set sensor gain to 96x
    mbl_mw_als_ltr329_set_gain(board, MBL_MW_ALS_LTR329_GAIN_96X);

    // Set the integration time to 400ms
    mbl_mw_als_ltr329_set_integration_time(board, MBL_MW_ALS_LTR329_TIME_400MS);

    // Set the measurement rate to 1000ms
    mbl_mw_als_ltr329_set_measurement_rate(board, MBL_MW_ALS_LTR329_RATE_1000MS);

    // Write the configuration to the sensor
    mbl_mw_als_ltr329_write_config(board);
}

Illuminance Measurement

To start measuring illuminance, call mbl_mw_als_ltr329_start. Illuminance data is represented as an unsigned integer and is in units of milli lux.

#include "metawear/core/datasignal.h"

void setup_illuminance_stream(MblMwMetaWearBoard* board) {
    auto data_handler = [](const MblMwData* data) -> void {
        // Cast value to uint32_t*
        printf("%dmlx\n", *((uint32_t*) data->value));
    };
    auto acc_signal= mbl_mw_als_ltr329_get_illuminance_data_signal(board);

    mbl_mw_datasignal_subscribe(acc_signal, data_handler);
    mbl_mw_als_ltr329_start(board);
}