Base Data Streams

The following page contains details of all base streams. These streams are not derived from any other streams and can be turned on independently of one another unless otherwise noted. Enabling/disabling these streams automatically turns on/off the required sensors.


Signal

Detects whether an EEG signal is present. When present, this stream emits a value of 1 and a value of 0 if not. Note that this doesn't necessarily indicate that Aurora is being worn on the head, rather it is just an indication that some voltage difference is present between the sensor leads. Enabling this stream automatically powers on Aurora's EEG/ECG bio-sensor.

Id Name Sample Rate Type Description
0 signal 1 sec/sample uint8 0 = no signal, 1 = signal present

Configuration Options

Config Id Option Default Value Values
0 Output Buffer Size 1 >= 1 (limited by available RAM)
1 File Buffer Size 128 bytes >= 128 (limited by available RAM)
2 Sample Rate 1 sec/sample >= 1*
3 Sync Interval 5000ms >= 0

* Sample rates > 1 are estimated using an average of samples taken at 1 second intervals.



EEG

This is the raw EEG value as measured by the Aurora bio-sensor's ADC after undergoing amplification (gain = 128) and minor filtering. The sensor employs a notch filter to reduce 50hz and 60hz power supply noise and a low-pass filter with stable band pass (0.5Hz – 100Hz). Montage used is FP1-FP2, (FPz reference). When there is no signal present, this value is considered noise/undefined.

Id Name Sample Rate Type Description
1 eeg 128 Hz int16 Raw EEG value* [-32768, 32767]

* Voltage at the input can be calculated by multiplying the raw EEG value by 0.143uV.

Configuration Options

Config Id Option Default Value Values
0 Output Buffer Size 12 >= 12 (limited by available RAM)
1 File Buffer Size 1024 bytes >= 512 (limited by available RAM)
2 Sample Rate 128 Hz 32,64,128,256,512*
3 Sync Interval 500ms >= 0

* Sample rates < 512 Hz are estimated by dropping samples at regular intervals, i.e. at 128 Hz, the bio-sensor continues to sample at 512 Hz but discards every 3rd sample.



Heart Rate

Estimated heart rate as calculated by Aurora's bio-sensor. For various reasons, this value should be considered experimental/unreliable and is provided mainly in the hopes of improving its accuracy in the future using more sophisticated techniques rather than relying on the sensor's output directly.

Id Name Sample Rate Type Description
2 heart 15 sec/sample uint8 Heart rate (BPM) [24, 200]

Configuration Options

Config Id Option Default Value Values
0 Output Buffer Size 1 >= 1 (limited by available RAM)
1 File Buffer Size 128 bytes >= 128 (limited by available RAM)
2 Sample Rate 15 sec/sample [1, 300]*
3 Sync Interval 5000ms >= 0

* Sample rates > 1 are estimated using an average of samples taken at 1 second intervals.



Accelerometer

Accelerometer X,Y,Z values as measured by Aurora's 6-axis accelerometer/gyroscope motion-sensor with a sensitivity of +-2g. In perfect conditions with the Aurora worn normally during sleep while laying on one's back, X and Y values should be close to zero, while the Z value should be close to -16384, or -1g.

Additionally, accelerometer magnitude and standard deviation are provided as derived streams accel-mag and accel-std respectively.

Id Name Sample Rate Type Description
3 accel-x 125 Hz int16 X-axis value, +-2g [-32768, 32767]*
4 accel-y 125 Hz int16 Y-axis value, +-2g [-32768, 32767]*
5 accel-z 125 Hz int16 Z-axis value, +-2g [-32768, 32767]*

* Actual acceleration (in terms of gravity) can be calculated by dividing the raw values by 16384.

Configuration Options

Config Id Option Default Value Values
0 Output Buffer Size 12 >= 12 (limited by available RAM)
1 File Buffer Size 1024 bytes >= 512 (limited by available RAM)
2 Sample Rate* 125 hz 125, 250, 500, 1000
3 Sync Interval 768ms >= 0

* Because the accelerometer and gyroscope data is generated from a single sensor, sample rate configuration applies to all accelerometer and gyroscope streams. i.e. setting the accel-x sample rate to 125Hz will also set the sample rate of the gyro-z stream (and all other accel/gyro streams).



Gyroscope

Gyroscope X,Y,Z values (aka angular velocity) as measured by Aurora's 6-axis motion-sensor with a sensitivity of +-250dps. If perfectly still, X,Y, and Z values should all be close to zero.

Additionally, gyroscope magnitude and 3d roll/pitch are provided as derived streams gyro-mag and 3d-roll/3d-pitch respectively.

Id Name Sample Rate Type Description
6 gyro-x 125 Hz int16 X-axis value, +-250dps [-32768, 32767]*
7 gyro-y 125 Hz int16 Y-axis value, +-250dps [-32768, 32767]*
8 gyro-z 125 Hz int16 Z-axis value, +-250dps [-32768, 32767]*

* Actual angular velocity (in degrees per second) can be calculated by dividing the raw values by 32768 / 250 or approximately 131.

Configuration Options

Config Id Option Default Value Values
0 Output Buffer Size 12 >= 12 (limited by available RAM)
1 File Buffer Size 1024 bytes >= 512 (limited by available RAM)
2 Sample Rate* 125 Hz 125, 250, 500, 1000
3 Sync Interval 768ms >= 0

* Because the accelerometer and gyroscope data is generated from a single sensor, sample rate configuration applies to all accelerometer and gyroscope streams. i.e. setting the gyro-x sample rate to 125Hz will also set the sample rate of the accel-z stream (and all other accel/gyro streams).



Temperature

Estimated internal temperature of Aurora as reported by the onboard temperature sensor built-in to the 6-axis acceleromter/gyroscope motion sensor. Theoretically this could be used to estimate ambient temperature, however because the Aurora's CPU will warm up with extended use this would need to be compensated for before such values could be considered reliable. Enabling this stream will enable the motion sensor, albeit in a lower power mode than if any accelerometer or gyroscope streams were also enabled.

Id Name Sample Rate Type Description
9 temperature 30 sec/sample float Aurora's internal temperature in degrees Celsius.

Configuration Options

Config Id Option Default Value Values
0 Output Buffer Size 1 >= 1 (limited by available RAM)
1 File Buffer Size 128 bytes >= 128 (limited by available RAM)
2 Sample Rate 30 sec/sample [1, 3600]*
3 Sync Interval N/A Not supported

* Sample rates > 1 are estimated using an average of samples taken at 1 second intervals.



Battery

Id Name Sample Rate Type Description
10 batt 1 min/sample uint16 Current battery voltage, in mV.

Configuration Options

Config Id Option Default Value Values
0 Output Buffer Size 1 >= 1 (limited by available RAM)
1 File Buffer Size 128 bytes >= 128 (limited by available RAM)
2 Sample Rate 30 min/sample [1, 60]*
3 Sync Interval N/A Not supported

* Sample rates > 1 are estimated using an average of samples taken at 1 minute intervals.



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