So we finally finished putting the polish on our latest Arduino library designed for use with the MMA8453Q Accelerometer and its siblings the MMA8451 and MMA8452. This library gets you going with the basics on this accelerometer and it also allows you to dig in a little deeper in to some of the advanced features, like motion detection and shake detection without much effort. This little QFN chip is not only cheap but its packed with 3 Axis’ of flavorful features. It’s on board 10 bit ADC coupled to the I2C interface means fast and accurate 3 axis measurements as well as built in free fall, pulse and jolt detection on programmable interrupt pins. As illustrated below, it’s a 3.3 volt part requiring additional level shifting to interface a 5 volt Arduino, this can be accomplished with a logic level N channel FET and a schottky diode:
So lets first get the library setup. Go ahead and download it from our github repo. The next thing you will need to do is download the wonderful and necessary i2c master library which our library depends on. This library is not only faster then the regular Arduino Wire library, it also follows the proper I2C specifications and allows for the sending of a repeated start bit which is required by the MMA845x family. So after you got both those libraries downloaded place them in your Arduino Libraries folder, and we are ready to get started.
When you fire up your Arduino app you will notice a new set of 4 examples in your examples menu. The first example we will take a look at is the ultra simple DataMode example. When you up up this sketch you will see right away just how simple it is, lets break it down anyway though, just in case.
At the top you will see the include of the library and its dependency library, the i2C lib, and the instantiation of the accel object.
#include <I2C.h> #include <MMA8453_n0m1.h> MMA8453_n0m1 accel;
In the setup function, you call the function dataMode to set the accelerometer into raw data output mode. This function has 2 parameters. A boolean, which is true for high resolution mode (10bit), and false for low resolution mode (8bit). The next parameter is to set the range of gravitational force the accelerometer will be sensitive to. These values, are +/-2g(waving your project around in your hand), +/-4g(your drag racing project), or +/-8g(your atmosphere re-entry vehicle project).
After that there is almost nothing left to do. Just call the update function at the top of your loop, which retrieves the latest values from the accelerometer, then use those values however you feel.
accel.update(); Serial.println(accel.x()); Serial.println(accel.y()); Serial.println(accel.z());
Well that’s it! Expecting some fancy complex gravitational voodoo, matrix math or pointer arithmetic? Sorry to disappoint. I’ll try to step it up a little in the next example then…however there’s a good chance it will be almost as simple.