ADXL362 + Arduino: Using Interrupts to Implement Motion-Activated Sleep

This tutorial details, step-by-step, how to use an ADXL362 to put an Arduino in a low-power state when the circuit is not moving, and then power it back up when motion is detected.

Before you get started:

If you haven't already, make sure you are able to successfully complete the ADXL362 Arduino How-To tutorial, which will guide you through hookup, ADXL362 Arduino library installation, and uploading/executing the "ADXL362_SimpleRead" example. Any unresolved issues you have while working through the first tutorial will cause you trouble in this one.

Download the Rocket Scream Low Power Arduino Library:

I'm sure there are many good examples/libraries for putting your Arduino to sleep, but I have had good luck with Rocket Scream's Low Power Arduino library - download zip file here.

In my examples, I renamed the "Low-Power" top level library directory to "LowPower". (My environment doesn't like the hyphen... I'm not sure if it's an OS issue, or perhaps the hyphen worked fine on an older version of the Arduino software? Either way... please remove the hyphen to make the library work with my example code.)

Remember lessons learned while installing the ADXL362 Arduino library in previous tutorial. "LowPower" library folder should be placed in your <sketchbook>/libraries folder.

You libraries directory structure should look like the picture below. Go to ADXL362 Arduino How-To for a more detailed description of how to install Arduino libraries.

If you have it installed successfully, The Rocket Scream LowPower library will show up under Sketch -> Import Library -> LowPower (See image below):

Add interrupt connection between ADXL362 and Arduino:

This sleep example utilizes the INT1 pin of the ADXL362, and the Interrupt 0 (digital pin 2) on the Arduino. So, adding to the connections that were made on the previous tutorial, add a wire to connect INT1 pin on the ADXL362 to DP2 pin on the Arduino. See image below for an illustration of required connections:

More information about Arduino interrupts can be found at http://arduino.cc/en/Reference/AttachInterrupt

Upload ADXL362_MotionActivatedSleep sketch to Arduino:

Once you have completed steps above, uploading the ADXL362_MotionActivatedSleep example to your Arduino should be simple and straightforward. The Motion activated sleep example requires the LowPower library to be properly installed.

Open the example by clicking File -> Examples -> ADXL362 -> ADXL362_MotionActivatedSleep, as shown in image below:

Make sure you have the correct board and serial port selected (see previous tutorial) and click the Upload button, as illustrated below:

Observe awake/asleep activity on Serial Monitor:

Open the serial monitor, and watch as your circuit goes to sleep and wakes up, depending on if it's being shaken or moved.

In the example code, the circuit stays "on" for two seconds after it's been motionless, then shuts off. The on/off timing, as well as the motion threshold, can be changed by tweaking the activity/inactivity interrupt settings, which I've set with the setupDCActivityInterrupt and setupDCInactivityInterrupt functions.

Or, Observe awake/Asleep activity with a multimeter:

To measure overall current, I disconnected the Pro Mini Arduino from my PC and FTDI Basic, and connected a multimeter in series with a 4.5V battery supply - I connected the battery supply to the RAW pin of my Pro Mini Arduino. My quick observation was that the overall circuit consumes a little over 4mA while awake, and roughly 270uA while asleep.

This tutorial does not include a thorough investigation of what portions of the circuit are consuming what portion of the overall power dissipation. But in this example, the ADXL362 consumes less than 3uA while on, and 300nA while the circuit is "sleeping." (The ADXL362 current consumption varies slightly with output data rate, input voltage, and mode) Therefore, most of the overall current, awake or asleep, is being consumed by the Pro Mini Arduino. I'll leave it to the reader to conduct their own experiments regarding power consumption.

Images below - Current consumption while Pro Mini Arduino + ADXL362 circuit is "awake," and "asleep."

And, for even lower sleep power, use a Rocket Scream Ultra Mini Arduino-compatible

So, as much as I love, love, love the Pro Mini, I wasn't completely satisfied with the sleep current of my overall circuit. And, I probably could have hacked my Pro Mini to make a few improvements (removing the 10K resistor across VCC comes to mind), I instead decided to purchase a Rocket Scream Mini Ultra Arduino-compatible board, especially since I'm using their handy Arduino library for sleep modes.