micro:bit and MMA8451 accelerometer example

The MMA8451 is a low-power accelerometer with 14 bits of resolution, with the following features:

  • Embedded functions with flexible user-programmable options, configurable to two interrupt pins
  • Embedded interrupt functions for overall power savings relieving the host processor from continuously polling data
  • Access to both low-pass filtered data as well as high-pass filtered data, which minimizes the data analysis required for jolt detection and faster transitions
  • Inertial wake-up interrupt signals from any combination of the configurable embedded functions allowing the MMA8451Q to monitor events and remain in a low-power mode during periods of inactivity

Features

  • 1.95 to 3.6-volt supply voltage
  • 1.6 to 3.6-volt interface voltage
  • ±2g/±4g/±8g dynamically selectable full-scale
  • Output data rates (ODR) from 1.56 Hz to 800 Hz
  • 99 μg/√Hz noise
  • 14-bit and 8-bit digital output
  • I²C digital output interface (operates to 2.25 MHz with 4.7 kΩ pull-up)
  • Two programmable interrupt pins for seven interrupt sources
  • Three embedded channels of motion detection
    • Freefall or motion detection: one channel
    • Pulse detection: one channel
    • Jolt detection: one channel
  • Orientation (portrait/landscape) detection with programmable hysteresis
  • Automatic ODR change for auto-wake and return to sleep
  • 32 sample FIFO
  • High pass filter data available per sample and through the FIFO
  • Self-test

Again due to the size and package of the module its easier to buy a module, here is one that I purchased. All you need to do is solder on the header and then connect using wires from your module to your Wemos Mini, wiring connections later

 

 

Connection

I used the following connection from the module above to my Wemos Mini

micro:bit Connection Module Connection
3v3 VCC_IN
Gnd Gnd
P20 SDA
P19 SCL
microbit and mma8451
microbit and mma8451

 

Code

This requires the Adafruit library from https://github.com/adafruit/Adafruit_MMA8451_Library/archive/master.zip

I had to edit the Adafruit header file called Adafruit_MMA8451.h as my device was address 0x1c (28), I discovered this using an I2C scanner

#define MMA8451_DEFAULT_ADDRESS                 (0x1C)

#include <Wire.h>
#include "Adafruit_MMA8451.h"
#include <Adafruit_Sensor.h>
 
 
Adafruit_MMA8451 mma = Adafruit_MMA8451();
 
void setup(void) {
  Serial.begin(9600);
 
  Serial.println("Adafruit MMA8451 test!");
 
 
  if (! mma.begin()) {
    Serial.println("Couldnt start");
    while (1);
  }
  Serial.println("MMA8451 found!");
 
  mma.setRange(MMA8451_RANGE_2_G);
 
  Serial.print("Range = "); Serial.print(2 << mma.getRange());  
  Serial.println("G");
 
}
 
void loop() {
  // Read the 'raw' data in 14-bit counts
  mma.read();
  Serial.print("X:\t"); Serial.print(mma.x); 
  Serial.print("\tY:\t"); Serial.print(mma.y); 
  Serial.print("\tZ:\t"); Serial.print(mma.z); 
  Serial.println();
 
  /* Get a new sensor event */ 
  sensors_event_t event; 
  mma.getEvent(&event);
 
  /* Display the results (acceleration is measured in m/s^2) */
  Serial.print("X: \t"); Serial.print(event.acceleration.x); Serial.print("\t");
  Serial.print("Y: \t"); Serial.print(event.acceleration.y); Serial.print("\t");
  Serial.print("Z: \t"); Serial.print(event.acceleration.z); Serial.print("\t");
  Serial.println("m/s^2 ");
 
  /* Get the orientation of the sensor */
  uint8_t o = mma.getOrientation();
 
  switch (o) {
    case MMA8451_PL_PUF: 
      Serial.println("Portrait Up Front");
      break;
    case MMA8451_PL_PUB: 
      Serial.println("Portrait Up Back");
      break;    
    case MMA8451_PL_PDF: 
      Serial.println("Portrait Down Front");
      break;
    case MMA8451_PL_PDB: 
      Serial.println("Portrait Down Back");
      break;
    case MMA8451_PL_LRF: 
      Serial.println("Landscape Right Front");
      break;
    case MMA8451_PL_LRB: 
      Serial.println("Landscape Right Back");
      break;
    case MMA8451_PL_LLF: 
      Serial.println("Landscape Left Front");
      break;
    case MMA8451_PL_LLB: 
      Serial.println("Landscape Left Back");
      break;
    }
  Serial.println();
  delay(500);
 
}

 

Output

Open the serial monitor

X: 4686 Y: 2748 Z: 684
X: 10.80 Y: 6.11 Z: 0.21 m/s^2
Landscape Right Front

X: 1314 Y: -3198 Z: 2014
X: 2.01 Y: -7.75 Z: 5.52 m/s^2
Portrait Up Front

X: 2194 Y: 2762 Z: -2530
X: 6.57 Y: 7.33 Z: -2.77 m/s^2
Portrait Down Back

X: 2294 Y: 3182 Z: -392
X: 3.49 Y: 2.23 Z: 0.13 m/s^2
Landscape Right Back

X: 224 Y: 1324 Z: -2844
X: -2.46 Y: 7.03 Z: -9.81 m/s^2
Portrait Down Back

 

Links

Here is a link to the module
GY-45 MMA8451 Module Digital Triaxial Accelerometer High-precision Inclination Module