Joystick.cpp

00001 #include "Joystick.h"
00002 
00003 Joystick::Joystick(PinName vertPin,PinName horizPin,PinName clickPin)
00004 {
00005     vert = new AnalogIn(vertPin);
00006     horiz = new AnalogIn(horizPin);
00007     click = new InterruptIn(clickPin);
00008 }
00009 
00010 void Joystick::init()
00011 {
00012     // read centred values of joystick
00013     _x0 = horiz->read();
00014     _y0 = vert->read();
00015 
00016     // this assumes that the joystick is centred when the init function is called
00017     // if perfectly centred, the pots should read 0.5, but this may
00018     // not be the case and x0 and y0 will be used to calibrate readings
00019 
00020     // turn on pull-down for button -> this assumes the other side of the button
00021     // is connected to +3V3 so we read 1 when pressed and 0 when not pressed
00022     click->mode(PullDown);
00023     // we therefore need to fire the interrupt on a rising edge
00024     click->rise(callback(this,&Joystick::click_isr));
00025     // need to use a callback since mbed-os5 - basically tells it to look in this class for the ISR
00026     _click_flag = 0;
00027 
00028 }
00029 
00030 Direction Joystick::get_direction()
00031 {
00032     float angle = get_angle();  // 0 to 360, -1 for centred
00033 
00034     Direction d;
00035     // partition 360 into segments and check which segment the angle is in
00036     if (angle < 0.0f) {
00037         d = CENTRE;   // check for -1.0 angle
00038     } else if (angle < 22.5f) {  // then keep going in 45 degree increments
00039         d = N;
00040     } else if (angle < 67.5f) {
00041         d = NE;
00042     } else if (angle < 112.5f) {
00043         d = E;
00044     } else if (angle < 157.5f) {
00045         d = SE;
00046     } else if (angle < 202.5f) {
00047         d = S;
00048     } else if (angle < 247.5f) {
00049         d = SW;
00050     } else if (angle < 292.5f) {
00051         d = W;
00052     } else if (angle < 337.5f) {
00053         d = NW;
00054     } else {
00055         d = N;
00056     }
00057 
00058     return d;
00059 }
00060 
00061 // this method gets the magnitude of the joystick movement
00062 float Joystick::get_mag()
00063 {
00064     Polar p = get_polar();
00065     return p.mag;
00066 }
00067 
00068 // this method gets the angle of joystick movement (0 to 360, 0 North)
00069 float Joystick::get_angle()
00070 {
00071     Polar p = get_polar();
00072     return p.angle;
00073 }
00074 
00075 // get raw joystick coordinate in range -1 to 1
00076 // Direction (x,y)
00077 // North     (0,1)
00078 // East      (1,0)
00079 // South     (0,-1)
00080 // West      (-1,0)
00081 Vector2D Joystick::get_coord()
00082 {
00083     // read() returns value in range 0.0 to 1.0 so is scaled and centre value
00084     // substracted to get values in the range -1.0 to 1.0
00085     float x = 2.0f*( horiz->read() - _x0 );
00086     float y = 2.0f*( vert->read() - _y0 );
00087 
00088     // Note: the x value here is inverted to ensure the positive x is to the
00089     // right. This is simply due to how the potentiometer on the joystick
00090     // I was using was connected up. It could have been corrected in hardware
00091     // by swapping the power supply pins. Instead it is done in software so may
00092     // need to be changed depending on your wiring setup
00093 
00094     Vector2D coord = {-x,y};
00095     return coord;
00096 }
00097 
00098 // This maps the raw x,y coord onto a circular grid.
00099 // See:  http://mathproofs.blogspot.co.uk/2005/07/mapping-square-to-circle.html
00100 Vector2D Joystick::get_mapped_coord()
00101 {
00102     Vector2D coord = get_coord();
00103 
00104     // do the transformation
00105     float x = coord.x*sqrt(1.0f-pow(coord.y,2.0f)/2.0f);
00106     float y = coord.y*sqrt(1.0f-pow(coord.x,2.0f)/2.0f);
00107 
00108     Vector2D mapped_coord = {x,y};
00109     return mapped_coord;
00110 }
00111 
00112 // this function converts the mapped coordinates into polar form
00113 Polar Joystick::get_polar()
00114 {
00115     // get the mapped coordinate
00116     Vector2D coord = get_mapped_coord();
00117 
00118     // at this point, 0 degrees (i.e. x-axis) will be defined to the East.
00119     // We want 0 degrees to correspond to North and increase clockwise to 359
00120     // like a compass heading, so we need to swap the axis and invert y
00121     float x = coord.y;
00122     float y = coord.x;
00123 
00124     float mag = sqrt(x*x+y*y);  // pythagoras
00125     float angle = RAD2DEG*atan2(y,x);
00126     // angle will be in range -180 to 180, so add 360 to negative angles to
00127     // move to 0 to 360 range
00128     if (angle < 0.0f) {
00129         angle+=360.0f;
00130     }
00131 
00132     // the noise on the ADC causes the values of x and y to fluctuate slightly
00133     // around the centred values. This causes the random angle values to get
00134     // calculated when the joystick is centred and untouched. This is also when
00135     // the magnitude is very small, so we can check for a small magnitude and then
00136     // set the angle to -1. This will inform us when the angle is invalid and the
00137     // joystick is centred
00138 
00139     if (mag < TOL) {
00140         mag = 0.0f;
00141         angle = -1.0f;
00142     }
00143 
00144     Polar p = {mag,angle};
00145     return p;
00146 }
00147 
00148 bool Joystick::button_pressed()
00149 {
00150     // ISR must have been triggered
00151     if (_click_flag) {
00152         _click_flag = 0;  // clear flag
00153         return true;
00154     } else {
00155         return false;
00156     }
00157 }
00158 
00159 void Joystick::click_isr()
00160 {
00161     _click_flag = 1;
00162 }