memsic 2125

Forum 2005-2010 (read only) Hardware Interfacing
#1

Hi,

I am trying to read the acceleration data from the memsic 2125, and the code from here doesn’t work the way I expect, so I’ve borrowed and modified some other code to get what I want:

int xPin = 5;      //  x-axis input (pin 5 from memsic)
int yPin = 4;      //  y-axis input (pin 2 from memsic)


unsigned long xDuration;
unsigned long yDuration;
unsigned long xLow;
unsigned long yLow;



unsigned long xAccel;
unsigned long yAccel;

/* (int) Operate Acceleration
* function to calculate acceleration
* returns a float so that precision isn't lost
* by dividing time2 by 1000.0 puts the overall value on a 1000.0 point scale.
*/
float operateAcceleration(int time1,int time2) {
  //Serial.print(time1);
return 8.0 * ((float)time1 / ((float)time2/1000.0) - 500.0);
}


void setup() {
  beginSerial(9600);
  pinMode(xPin, INPUT);
  pinMode(yPin, INPUT);
}

void loop(){
  
  yDuration = pulseIn(yPin, HIGH); // pulseIn gives the time in microseconds
 yLow = pulseIn(yPin,LOW);

  xDuration = pulseIn(xPin, HIGH);
xLow = pulseIn(xPin,LOW); 

  xAccel = (int)operateAcceleration(xDuration,xDuration+xLow); // estimate time2 for x
  yAccel = (int)operateAcceleration(yDuration,yDuration+yLow); // estimate time2 for y
  

  
  //serialWrite('Y');
  //serialWrite('-');
  Serial.print("Y,X: ");
  //printInteger(yDuration);
  //Serial.print(" LOW:");
 // printInteger(yLow);
  //Serial.print("ms ");
//Serial.print(" Total: ");
 // printInteger(yDuration+yLow);
 // serialWrite(' ');
   
  printInteger(yAccel);
 // Serial.print(" accel");
  //printByte(10);
 
 

 
Serial.print(",");
  //printInteger(xDuration);
  //Serial.print(" LOW:");
  //printInteger(xLow);
  //Serial.print(" Total: ");
  //printInteger(xDuration+xLow);
  //serialWrite('X');
  //serialWrite(' ');
  //printInteger(xDuration);
  //Serial.print("ms ");
  printInteger(xAccel);
  //Serial.print(" accel");
  printByte(10);
  delay(100);
  
}

I have followed the instructions from page 70-71 of this document to test if the code is working, except the difference is that the X and Y values should be from -1000 to 1000 instead of from 1875 to 3125.

I get the following results:

When tilting the x axis, I get values around -1000, 0 , and 1000 (+/- around 100)
When tilting the y axis, I get values around -3000 (+/- 1000), as I approach level the values sometimes approach 0, and as I tilt up, I get values around 1000 (+/- 500).

I can’t figure out why I would be getting such noisy values for y but not for x.

Any ideas?

thanks.

David

#2