I have the MMA8452Q accelerometer [breakout board and I’m using it with a Leonardo. I started out testing the [Basic Example sketch which seems to work okay, but I can’t get it to work with my sketch, which is very similar. The main difference is I’m not converting the accelerometer outputs to G values, but printing the raw numbers. The Leonardo keeps locking up after a few seconds. It will usually (not always) start out working, but after a few seconds to a minute, it locks up. The same sketch seems to run fine on the Duemilanove. I have the I2C wired as suggesting in the example sketch with 330 ohm resistors in-line on the SDA and SCL lines. They are not wired like pull-ups, but inline to reduce the voltage. The breakout board already has pull-ups. I’ve only made changes in setup() and loop(), all the other functions are the same as the MMA8452Q_BasicExample.ino sketch. On the Duemilanove I have I2C on pins A4 and A5, on the Leonardo, I have it connected to the dedicated SDA/SCL pins.
Here’s the sketch that’s giving me problems:
#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 PCBLED 13
#define GSCALE 2 // Sets full-scale range to +/-2, 4, or 8g. Used to calc real g values.
uint32_t heartBeatTmr;
void setup()
{
Serial.begin(9600);
while (!Serial && millis() < 8000) {}
Serial.println(F("MMA8452 Basic Example"));
pinMode(PCBLED, OUTPUT);
digitalWrite(PCBLED, LOW);
Wire.begin(); // Join the bus as a master
initMMA8452(); // Test and intialize the MMA8452
heartBeatTmr = millis() + 5000;
}
void loop()
{
int accelCount[3]; // Stores the 12-bit signed value
readAccelData(accelCount); // Read the x/y/z adc values
if(accelCount[0] < -400 || accelCount[0] > 400 || accelCount[1] < -400 || accelCount[1] > 400 )
{
// Print out values
Serial.print(accelCount[0]);
Serial.print("\t");
Serial.print(accelCount[1]);
Serial.print("\t");
Serial.println(accelCount[2]);
// Flash PCB LED
digitalWrite(PCBLED, HIGH);
delay(200);
digitalWrite(PCBLED, LOW);
heartBeatTmr = millis() + 5000;
}
if ((long)(millis() - heartBeatTmr) > 0)
{
Serial.print("Heartbeat ");
heartBeatTmr = millis() + 5000;
}
} // end loop()
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...");
}
else
{
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.beginTransmission(MMA8452_ADDRESS);
Wire.write(addressToRead);
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.beginTransmission(MMA8452_ADDRESS);
Wire.write(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.beginTransmission(MMA8452_ADDRESS);
Wire.write(addressToWrite);
Wire.write(dataToWrite);
Wire.endTransmission(); //Stop transmitting
}
](http://github.com/sparkfun/MMA8452_Accelerometer/tree/master/Firmware/MMA8452Q_BasicExample)](Triple Axis Accelerometer Breakout - MMA8452Q - SEN-10955 - SparkFun Electronics)