Ruben Laguna’s blog

Arduino Library for MMA7260Q (Tilt Sensor)

In the past days I published a couple of arduino libraries. All coming from by XBee sensor development. I’m still waiting for the MAX756 to arrive from Futurlec, I need the MAX756 to power the xbee sensor with batteries and mount it in its final position. So in the meanwhile I’m cleaning a little bit the code, moving thing to libraries, etc. Now it’s the turn of the MMA7260Q, (see other posts about MMA7260q) .

I created an Arduino library to use MMA7260Q as a Tilt Sensor that does autozero calibration.

The library contains an example that can be accessed through the File ⇒ Sketchbook ⇒ Examples ⇒ Library-Mma7260q ⇒ SimpleTiltSensor.

SimpleTiltSensor library

The example looks like this (also available as gist):

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<span class='line'>#include "mma7260q.h"
</span><span class='line'>
</span><span class='line'>//set up MMA7260Q
</span><span class='line'>Mma7260q mma7260q = Mma7260q(0,1,2);
</span><span class='line'>
</span><span class='line'>long time = millis();
</span><span class='line'>
</span><span class='line'>void setup()  {  
</span><span class='line'>  
</span><span class='line'>  Serial.begin(9600);
</span><span class='line'>  delay(100);
</span><span class='line'>  
</span><span class='line'>  
</span><span class='line'>  //initial calibration of the MMA7260q 
</span><span class='line'>  // you can get the correct values for your MMA7260q
</span><span class='line'>  // by running this program and copying the max and min values
</span><span class='line'>  // after rotating the mma7260q 360degrees around all axis
</span><span class='line'>  mma7260q.autoZeroCalibration(173,192,258);
</span><span class='line'>  mma7260q.autoZeroCalibration(766,720,914);
</span><span class='line'>  
</span><span class='line'>  
</span><span class='line'>  Serial.print("RST\r\n");delay(100);  
</span><span class='line'>}
</span><span class='line'>
</span><span class='line'>
</span><span class='line'>void loop() 
</span><span class='line'>{
</span><span class='line'>     float rho, phi,theta;
</span><span class='line'>     mma7260q.readTilt(&rho,&phi,&theta);
</span><span class='line'>     
</span><span class='line'>     if ((millis()-time)>2000)
</span><span class='line'>     {
</span><span class='line'>       time = millis();
</span><span class='line'>       Serial.print("rho : ");
</span><span class='line'>       printFloat(rho,3);
</span><span class='line'>       Serial.print(" phi : ");
</span><span class='line'>       printFloat(phi,3);
</span><span class='line'>       Serial.print(" the: ");
</span><span class='line'>       printFloat(theta,3);
</span><span class='line'>       Serial.print("\r\n");    
</span><span class='line'> 
</span><span class='line'>       int minx,miny,minz,maxx,maxy,maxz;
</span><span class='line'>       mma7260q.getMinValues(&minx,&miny,&minz);
</span><span class='line'>       mma7260q.getMaxValues(&maxx,&maxy,&maxz);
</span><span class='line'>       Serial.print("minx: ");
</span><span class='line'>       Serial.print((int)minx,DEC);
</span><span class='line'>       Serial.print(" miny: ");
</span><span class='line'>       Serial.print((int)miny,DEC);
</span><span class='line'>       Serial.print(" minz: ");
</span><span class='line'>       Serial.print((int)minz,DEC);
</span><span class='line'>       Serial.print("\r\n");
</span><span class='line'>  
</span><span class='line'>       Serial.print("maxx: ");
</span><span class='line'>       Serial.print((int)maxx,DEC);
</span><span class='line'>       Serial.print(" maxy: ");
</span><span class='line'>       Serial.print((int)maxy,DEC);
</span><span class='line'>       Serial.print(" maxz: ");
</span><span class='line'>       Serial.print((int)maxz,DEC);
</span><span class='line'>       Serial.print("\r\n");
</span><span class='line'> 
</span><span class='line'>     }
</span><span class='line'>}
</span><span class='line'>
</span><span class='line'>void printFloat(float value, int places) {
</span><span class='line'>   // this is used to cast digits
</span><span class='line'>   int digit;
</span><span class='line'>   float tens = 0.1;
</span><span class='line'>   int tenscount = 0;
</span><span class='line'>   int i;
</span><span class='line'>   float tempfloat = value;
</span><span class='line'>
</span><span class='line'>   // if value is negative, set tempfloat to the abs value
</span><span class='line'>   // make sure we round properly. this could use pow from  
</span><span class='line'>   //&lt;math.h>, but doesn't seem worth the import
</span><span class='line'>   // if this rounding step isn't here, the value  54.321 prints as  
</span><span class='line'>   //54.3209
</span><span class='line'>
</span><span class='line'>   // calculate rounding term d:   0.5/pow(10,places)
</span><span class='line'>   float d = 0.5;
</span><span class='line'>   if (value &lt; 0)
</span><span class='line'>     d *= -1.0;
</span><span class='line'>   // divide by ten for each decimal place
</span><span class='line'>   for (i = 0; i &lt; places; i++)
</span><span class='line'>     d/= 10.0;
</span><span class='line'>   // this small addition, combined with truncation will round our  
</span><span class='line'>   // values properly
</span><span class='line'>   tempfloat +=  d;
</span><span class='line'>
</span><span class='line'>   // first get value tens to be the large power of ten less than value
</span><span class='line'>   // tenscount isn't necessary but it would be useful if you wanted  
</span><span class='line'>   // to know after this how many chars the number will take
</span><span class='line'>
</span><span class='line'>   if (value &lt; 0)
</span><span class='line'>     tempfloat *= -1.0;
</span><span class='line'>   while ((tens * 10.0) &lt;= tempfloat) {
</span><span class='line'>     tens *= 10.0;
</span><span class='line'>     tenscount += 1;
</span><span class='line'>   }
</span><span class='line'>
</span><span class='line'>
</span><span class='line'>   // write out the negative if needed
</span><span class='line'>   if (value &lt; 0)
</span><span class='line'>     Serial.print('-');
</span><span class='line'>
</span><span class='line'>   if (tenscount == 0)
</span><span class='line'>     Serial.print(0, DEC);
</span><span class='line'>
</span><span class='line'>   for (i=0; i&lt; tenscount; i++) {
</span><span class='line'>     digit = (int) (tempfloat/tens);
</span><span class='line'>     Serial.print(digit, DEC);
</span><span class='line'>     tempfloat = tempfloat - ((float)digit * tens);
</span><span class='line'>     tens /= 10.0;
</span><span class='line'>   }
</span><span class='line'>
</span><span class='line'>   // if no places after decimal, stop now and return
</span><span class='line'>   if (places &lt;= 0)
</span><span class='line'>     return;
</span><span class='line'>
</span><span class='line'>   // otherwise, write the point and continue on
</span><span class='line'>   Serial.print('.');
</span><span class='line'>
</span><span class='line'>   // now write out each decimal place by shifting digits one by one  
</span><span class='line'>   // into the ones place and writing the truncated value
</span><span class='line'>   for (i = 0; i &lt; places; i++) {
</span><span class='line'>     tempfloat *= 10.0;
</span><span class='line'>     digit = (int) tempfloat;
</span><span class='line'>     Serial.print(digit,DEC);
</span><span class='line'>     // once written, subtract off that digit
</span><span class='line'>     tempfloat = tempfloat - (float) digit;
</span><span class='line'>   }
</span><span class='line'>}</span>


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