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.


The LTR329 sensor has 3 configurable parameters:




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.

// 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

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.

let signal = mbl_mw_als_ltr329_get_illuminance_data_signal(device.board)!
mbl_mw_datasignal_subscribe(signal, bridge(obj: self)) { (context, obj) in
    let illuminance: UInt32 = obj!.pointee.valueAs()
    print(String(format: "%.3f lux", Double(illuminance) / 1000.0))