The MetaWear board can log sensor data and store it in the internal memory of the device using loggers to be retrieved at a later time.

Loggers record data from a data signal and are represented by the MblMwDataLogger struct.

Create an MblMwDataLogger object by calling mbl_mw_datasignal_log with the data signal you want to log.

If successful, the callback function will be executed with a MblMwDataLogger pointer and if creating the logger failed, a null pointer will be returned.

var accSignal = MetaWear.mbl_mw_acc_get_acceleration_data_signal(device.board);

MetaWear.mbl_mw_datasignal_log(accSignal, ref.NULL, MetaWear.FnVoid_VoidP_DataLoggerP.toPointer(function (context, logger) {
    accelLogger = logger;
    callback(logger.address() ? null : new Error('failed to start logging accel'));

MblMwDataLogger objects only interact with the specific data signal, they do not control the logging features. Logging control functions are detailed in the Logging section.


MblMwDataLogger objects are identified by a numerical id.

This id can be used to keep track of loggers when there is considerable time between the start of a log and the download of a log. It is also useful to get the state of the device (i.e is my device still downloading?).

You can retrieve the id by calling mbl_mw_logger_get_id.

The id is used to retrieve existing loggers from the API with the mbl_mw_logger_lookup_id function.

Handling Data

Like a data signal, you can subscribe to an MblMwDataLogger to process the downloaded data.

Call mbl_mw_logger_subscribe to attach a callback function to the MblMwDataLogger which handles all received data.

// Subscribe to the accelerometer data
MetaWear.mbl_mw_logger_subscribe(accelLogger, ref.NULL, MetaWear.FnVoid_VoidP_DataP.toPointer(function onSignal(context, dataPtr) {
    var data = dataPtr.deref();
    var pt = data.parseValue();
    console.log(data.epoch + ' ' + pt.x + ',' + pt.y + ',' + pt.z);


When you no longer want to log the values from a data signal, call mbl_mw_logger_remove to remove the logger.