Help with HM55B Compass

as of right hm55b compass printing constant data processing -180 0n 180.  how modify following code output 8 directions. n, ne, e, se, s, sw, w, nw?

code: [select]


#include <math.h> // (no semicolon)
//// vars
byte clk_pin = 8;
byte en_pin = 9;
byte dio_pin = 10;
byte led = 13;

int zerooffset = 0;        // calibrate compass, run in uncalibrated mode [section 1],
                          // point sensor due north, , record value sensed.  
                          // enter value here , run in calibrated mode [section 2]
int x_data = 0;
int y_data = 0;
int angle, status;
float delta, xprime, yprime;


//// functions

void shiftout(int value, int bitscount) {
 for(int = bitscount; >= 0; i--) {
   digitalwrite(clk_pin, low);
   if ((value & 1 << i) == ( 1 << i)) {
     digitalwrite(dio_pin, high);
     //serial.print("1");
   }
   else {
     digitalwrite(dio_pin, low);
     //serial.print("0");
   }
   digitalwrite(clk_pin, high);
   delaymicroseconds(1);
 }
}

int shiftin(int bitscount) {
 int shiftin_result;
   shiftin_result = 0;
   pinmode(dio_pin, input);
   for(int = bitscount; >= 0; i--) {
     digitalwrite(clk_pin, high);
     delaymicroseconds(1);
     if (digitalread(dio_pin) == high) {
       shiftin_result = (shiftin_result << 1) + 1;
       //serial.print("x");
     }
     else {
       shiftin_result = (shiftin_result << 1) + 0;
       //serial.print("_");
     }
     digitalwrite(clk_pin, low);
     delaymicroseconds(1);
   }
 //serial.print(":");

// below difficult understand:
// if bit 11 set value negative
// representation of negative values you
// have add b11111000 in upper byte of
// integer.
// see: http://en.wikipedia.org/wiki/two%27s_complement
 if ((shiftin_result & 1 << 11) == 1 << 11) {
   shiftin_result = (b11111000 << 8) | shiftin_result;
 }


 return shiftin_result;
}

void hm55b_reset() {
 pinmode(dio_pin, output);
 digitalwrite(en_pin, low);
 shiftout(b0000, 3);
 digitalwrite(en_pin, high);
}

void hm55b_startmeasurementcommand() {
 pinmode(dio_pin, output);
 digitalwrite(en_pin, low);
 shiftout(b1000, 3);
 digitalwrite(en_pin, high);
}

int hm55b_readcommand() {
 int result = 0;
 pinmode(dio_pin, output);
 digitalwrite(en_pin, low);
 shiftout(b1100, 3);
 result = shiftin(3);
 return result;
}


void setup() {
 serial.begin(9600);
 pinmode(en_pin, output);
 pinmode(clk_pin, output);
 pinmode(dio_pin, input);
 serial.println();
 hm55b_reset();
}

void loop() {
 hm55b_startmeasurementcommand(); // necessary!!
 delay(40); // data 40ms later ready
 status = hm55b_readcommand(); // read data
 x_data = shiftin(11); // field strength in x
 y_data = shiftin(11); // , y direction
 digitalwrite(en_pin, high); // deselect chip

//  [section 1: simple angle calculation]
//  to determine angle using raw sensor data, can calculate
//  the inverse tangent of y_data/x_data.  uncomment following line , comment
//  all of [section 2]

//  angle = (180 * (atan2(-1 * y_data , x_data) / m_pi)); // angle atan( -y/x) !!!

//  [end section 1]


//  [section 2: offset-compensated angle calculation]
//  to better match compass readings known values of true north,
//  you can use following calculations rotate value of tangent
//  before determining angle.  to this, first need run program
//  with code in [section 1] uncommented , note angle value when we
//  point sensor true north.  enter value recorded @ top of
//  this program in variable "zerooffset", comment code in [section 1],
//  and uncomment code below.

 delta = (zerooffset/180.0)*m_pi;                      // calculate radians degrees
 xprime = x_data*cos(delta) - y_data*sin(delta);       // translate x_data value based on
                                                       // rotating original angle "delta" rads.
 yprime = y_data*cos(delta) + x_data*sin(delta);       // translate y_data value based on
                                                       // rotating original angle "delta" rads.
 angle = (180 * (atan2(-1 * yprime , xprime) / m_pi)); // angle still atan(-y/x)

//  [end section 2]

 if (abs(angle) < 10) {
   digitalwrite (led, high);
 } else {
   digitalwrite (led, low);
 }    
 
 serial.println(angle); // print angle
 delay(100);

}


assuming angle contains value between 0 , 359:

code: [select]

char* directions[]={"n", "ne", "e", "se", "s", "sw", "w", "nw"};

serial.println(directions[((angle+22)/45)%8]);

beware, though, haven't been able try it.

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