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GPS logger with accelerometer assistance
Moderators: adafruit_support_bill, adafruit

GPS logger with accelerometer assistance

by jcraig on Sun Feb 17, 2013 4:00 pm


First of all, thank you for making such an outstanding product! I

I was hoping I could get some help adding my MMA8452 accelerometer data to my version 1.0 GPS Logging shield. I have successfully tested the GPS module, and the accelerometer independently. I am currently using the GPS basic logging sketch with an Arduino UNO and it works perfectly. It looks like I should be using the CSV logging sketch to add the sensor values, but I get an error:

"As of Arduino 1.0, the 'BYTE' keyword is no longer supported.
Please use Serial.write() instead."

I also see that the sketch is set up for temperature values, and not accelerometer data.

Ideally I would like to be able to parse the data along with the gps data to be shown on google earth

This project is to record data from our rally car as it flies down the road : )

Here is the code I'm using for the accelerometer... Sorry if i've attached it in an annoying way, I'm new to this.

All the very best!


MMA8452Q Basic Example Code
Nathan Seidle
SparkFun Electronics
November 5, 2012
License: This code is public domain but you buy me a beer if you use this and we meet someday (Beerware license).
This example code shows how to read the X/Y/Z accelerations and basic functions of the MMA5842. It leaves out
all the neat features this IC is capable of (tap, orientation, and inerrupts) and just displays X/Y/Z. See
the advanced example code to see more features.
Hardware setup:
MMA8452 Breakout ------------ Arduino
3.3V --------------------- 3.3V
SDA -------^^(330)^^------- A4
SCL -------^^(330)^^------- A5
GND ---------------------- GND
The MMA8452 is 3.3V so we recommend using 330 or 1k resistors between a 5V Arduino and the MMA8452 breakout.
The MMA8452 has built in pull-up resistors for I2C so you do not need additional pull-ups.

#include <Wire.h> // Used for I2C

// The SparkFun breakout board defaults to 1, set to 0 if SA0 jumper on the bottom of the board is set
#define MMA8452_ADDRESS 0x1D // 0x1D if SA0 is high, 0x1C if low

//Define a few of the registers that we will be accessing on the MMA8452
#define OUT_X_MSB 0x01
#define XYZ_DATA_CFG 0x0E
#define WHO_AM_I 0x0D
#define CTRL_REG1 0x2A

#define GSCALE 2 // Sets full-scale range to +/-2, 4, or 8g. Used to calc real g values.

void setup()
  Serial.println("MMA8452 Basic Example");

  Wire.begin(); //Join the bus as a master

  initMMA8452(); //Test and intialize the MMA8452

void loop()
  int accelCount[3]; // Stores the 12-bit signed value
  readAccelData(accelCount); // Read the x/y/z adc values

  // Now we'll calculate the accleration value into actual g's
  float accelG[3]; // Stores the real accel value in g's
  for (int i = 0 ; i < 3 ; i++)
    accelG[i] = (float) accelCount[i] / ((1<<12)/(2*GSCALE)); // get actual g value, this depends on scale being set

  // Print out values
  for (int i = 0 ; i < 3 ; i++)
    Serial.print(accelG[i], 4); // Print g values
    Serial.print("\t"); // tabs in between axes

  delay(10); // Delay here for visibility

void readAccelData(int *destination)
  byte rawData[6]; // x/y/z accel register data stored here

  readRegisters(OUT_X_MSB, 6, rawData); // Read the six raw data registers into data array

  // Loop to calculate 12-bit ADC and g value for each axis
  for(int i = 0; i < 3 ; i++)
    int gCount = (rawData[i*2] << 8) | rawData[(i*2)+1]; //Combine the two 8 bit registers into one 12-bit number
    gCount >>= 4; //The registers are left align, here we right align the 12-bit integer

    // If the number is negative, we have to make it so manually (no 12-bit data type)
    if (rawData[i*2] > 0x7F)
      gCount = ~gCount + 1;
      gCount *= -1; // Transform into negative 2's complement #

    destination[i] = gCount; //Record this gCount into the 3 int array

// Initialize the MMA8452 registers
// See the many application notes for more info on setting all of these registers:
// http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MMA8452Q
void initMMA8452()
  byte c = readRegister(WHO_AM_I); // Read WHO_AM_I register
  if (c == 0x2A) // WHO_AM_I should always be 0x2A
    Serial.println("MMA8452Q is online...");
    Serial.print("Could not connect to MMA8452Q: 0x");
    Serial.println(c, HEX);
    while(1) ; // Loop forever if communication doesn't happen

  MMA8452Standby(); // Must be in standby to change registers

  // Set up the full scale range to 2, 4, or 8g.
  byte fsr = GSCALE;
  if(fsr > 8) fsr = 8; //Easy error check
  fsr >>= 2; // Neat trick, see page 22. 00 = 2G, 01 = 4A, 10 = 8G
  writeRegister(XYZ_DATA_CFG, fsr);

  //The default data rate is 800Hz and we don't modify it in this example code

  MMA8452Active(); // Set to active to start reading

// Sets the MMA8452 to standby mode. It must be in standby to change most register settings
void MMA8452Standby()
  byte c = readRegister(CTRL_REG1);
  writeRegister(CTRL_REG1, c & ~(0x01)); //Clear the active bit to go into standby

// Sets the MMA8452 to active mode. Needs to be in this mode to output data
void MMA8452Active()
  byte c = readRegister(CTRL_REG1);
  writeRegister(CTRL_REG1, c | 0x01); //Set the active bit to begin detection

// Read bytesToRead sequentially, starting at addressToRead into the dest byte array
void readRegisters(byte addressToRead, int bytesToRead, byte * dest)
  Wire.endTransmission(false); //endTransmission but keep the connection active

  Wire.requestFrom(MMA8452_ADDRESS, bytesToRead); //Ask for bytes, once done, bus is released by default

  while(Wire.available() < bytesToRead); //Hang out until we get the # of bytes we expect

  for(int x = 0 ; x < bytesToRead ; x++)
    dest[x] = Wire.read();

// Read a single byte from addressToRead and return it as a byte
byte readRegister(byte addressToRead)
  Wire.endTransmission(false); //endTransmission but keep the connection active

  Wire.requestFrom(MMA8452_ADDRESS, 1); //Ask for 1 byte, once done, bus is released by default

  while(!Wire.available()) ; //Wait for the data to come back
  return Wire.read(); //Return this one byte

// Writes a single byte (dataToWrite) into addressToWrite
void writeRegister(byte addressToWrite, byte dataToWrite)
  Wire.endTransmission(); //Stop transmitting

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