Motion intelligence on the edge leads to lower power consumption

27 April 2016

Some of the biggest challenges with IoT-systems and wearable technologies are power consumption and battery life.

By using SensorBeat technology, we can lower power consumption and extend the battery life. This is because the SensorBeat software runs on the device, and that the device understands motion (motion intelligence on the edge). This reduces the need to transmit data over Bluetooth LE or other methods (2G/3G/4G/WiFi) which all are very power hungry.

Motion intelligence on the edge gives us a number of distinct benefits:

Less data to transmit
Less frequent transmitting of data
Better quality in the transmitted data
Lower costs for data transmission
Less need for central data storage and analytics
These benefits leads to lower power consumption and extended battery life.

We have calculated the power consumption of the SensorBeat software running on the device. The calculations are theoretical and are based on how SensorBeat works and the technical specifications from the manufacturers of the components in our device.

We are well aware of that these calculations are a little bit simplified, but they can still be used as a guideline.

Microprocessor: ARM-Cortex M0
Accelerometer: Invensense MPU-9250
Resolution: 14-bit
Frequency: 10 Hz
Range: +/- 8G
FIFO-depth: 32 samples

Power consumption when running SensorBeat
Device in extended sleep and wake on motion activated: 9.2 µA
Device in motion with ARM-Cortex M0 @16 Mhz + Invensense MPU-9250 @ 10 Hz: 70 µA -130 µA
Voltage: 1,8 V

Example: A device that is in sleep 60 % of the time and in motion 40 % of the time will have a power consumption of: 0.6 * 9,2 µA + 0.4 * 100 µA (average consumption when in motion) = 5,5 µA + 40 µA = 45,5 µA

Power consumption when transmitting via Bluetooth
Device when transmitting: 5 mA

Example: Transmitting 0,1 % of the time (=3,6 seconds/hour) : 0,001* 5 mA = 5 µA
A device that is in sleep mode 60 % of the time, in motion 40 % of the time and transmitting 0,1 % of the time: 45,5 µA + 5 µA = 50,5 µA

How to calculate battery time
Assume battery with 3,7 V, 510 mAh
Consumption (from example above): 50,5 µA * 1,8 V = 90,9 µW
Battery: 3,7 V * 510 mAh = 1 887 mWh
Battery time: 1 887 mWh/90,9 µW = 29 months