How does an Android process sense motion?

The Android 4.4 Operating System from Google is able to track your motion in real-time. You can test this with the Google-map application when traveling – your current position as shown on the map will shift as you move. Although this was feature available earlier as well, Google has mandated that 4.4 version onwards, Android will be using this function in the background while it has turned the application processor off. Google has introduced this change to save battery life.

To comply with this mandate, manufacturers will now have to offload this function from the application processor and transfer it to a sensor hub. In anticipation of this mandate from Google, InvenSense has already transferred those functions into their patented DMP or Digital Motion Processor, which they have announced as their six-axis MEMS combo processor for an accelerometer and a gyroscope. Therefore, smart sensors will be providing the real-time contextual awareness functions in the background of your smartphone, while its screen is switched off.

This can be done in one of two ways. One of them may be to allow several new sensor functions to be run in a sensor hub. However, this has the disadvantage of adding cost to the product. A much better way, followed by InvenSense, is to include the processing within the sensor itself, which means smartening up the sensors. The MPU-8515 is a six-axis digital motion processor developed by InvenSense for this purpose.

Inside the MPU-6515, there is a three-axis gyroscope along with a three-axis accelerometer housed within the same package. With an enhanced version of their DMP built into their MPU, InvenSense is able to handle the specific functions that the Android operating system mandates running external to the application processor. With the MPU-6515, sensors can remain on for more time and supply more real-time data for location and context awareness yet reduce battery consumption.

In practice, the Android operating system shuts down the application processor when there is no activity input from the screen. It wakes up only when it receives a significant motion interrupt while rejecting false triggers to switch the application processor back on. Significant motions include pedometric functions such as detecting and counting steps while running in the background.

Processing information accurately when the application processor is turned off involves inertial location tracking. That requires processing rotation vectors involving six axes. The MPU-6515 does this by amalgamating the outputs of three axes from the gyroscope and three axes from the accelerometer sensors and buffering them periodically between the significant motion interrupts using a new batch mode.

The MPU-6515 can work in both modes – with a hub or in a hub less mode. This additional functionality is helpful for situations where the Android operating system has turned off both the application processor and the hub. Using this combo gyroscope and accelerometer chip with enhanced digital motion processor, InvenSense has been able to enhance its handling of contextual awareness for the Android operating system.

Manufacturers can easily use the MPU-6515, measuring a mere 3x3x0.9 mm, in smartphones, wearables, tablets and in devices for Internet of Things. Those using the earlier device from InvenSense, the MPU-6500 can easily replace the older chip as both are pin-compatible.