Use the AWT function to realize the function of raising the screen and turning the screen with a simple hardware register configuration.

Recently, gesture recognition has been increasingly valued by mobile phones and smart wearable device manufacturers, and the functions of raising the screen and turning the wrist screen are gradually becoming the basic functions of many mobile phones and watch products.

There is no doubt that sensor data and software algorithms can be used to achieve similar functions, but this requires the sensor hub to work continuously (alwayson), resulting in additional power consumption. For some smart wearable products, it is limited by the battery capacity, which is very Hard to accept. ST has added AWT (AbsoluteWrist Tilt) function on LSM6DSL/M, which can realize the function of raising the screen and turning the screen with simple hardware register configuration, and the overall power consumption is only 20-30 microamperes, which is relative to sensor. The similar power of the hub is almost negligible compared to the power consumption of a few milliamps.

The AWT function uses accelerometer data with a sampling rate of 26 Hz. The user can define a half-axis threshold (which can be converted into an angle) and duration. When the accelerometer rotates its output for more than the threshold and exceeds the specified time, the output interrupts to wake up the host. The host can be illuminated according to its own definition. Screen and other operations. Because different product definitions and patch orientations are different, AWT allows the user to choose to detect a half-axis signal or to monitor multiple half-axes simultaneously.

More specifically, using the AWT function is very simple, only 6 steps, 1) turn on the accelerometer, 2) start AWT, 3) configure the AWT interrupt pin, 4) configure the sense axis, 5) configure the threshold, 6 ) Configuration duration.

Among them, since the unit of acceleration is g or mg, the following formula is needed to convert it into an angle, as follows:

For example, the default initial threshold of LSM6DSL is 20h, which is 500mg, and its corresponding angle is 30 degrees .

The above figure is an example of the use of the AWT function. The example configuration detects the positive rotation of the X axis. It can be seen that the trigger condition is met each time, that is, when the X axis positive tilt angle exceeds 30 degrees and continues for a while, the sensor will generate an interrupt. When other interference signals appear, no interrupt signal is generated.

Finally, there are currently three 6-axis sensors that support the AWT function, namely LSM6DSL, LSM6DSM and LSM6DS3-C. In addition, for users who only need an accelerometer, consider using LIS3DSH to achieve similar functionality. Although the LIS3DSH itself does not have AWT functionality, it has two programmable state machines that can be implemented by configuring a hardware state machine.