JSN_SR04.cpp

00001 #include "mbed.h"
00002 #include "JSN_SR04.h"
00003 
00004 JSN_SR04::JSN_SR04(PinName echoPin, PinName triggerPin) : echo(echoPin), trigger(triggerPin) {
00005     init();
00006 }
00007 
00008 void JSN_SR04::init() {
00009     distance = -1;                                      // Default distance
00010     minDistance = 2;                                        // Default min boundary
00011     maxDistance = 400;                                  // Default max boundary
00012     newDataReady = timerStarted = false;            // Indicators are false by default
00013 }
00014 
00015 void JSN_SR04::startTimer() {
00016     // Check if the timer started
00017    if (!timerStarted) {
00018          // start the timer
00019        timer.start();
00020        timerStarted = true;
00021 
00022          // Call the stopTimer() method after a predefined timeout (> 25 ms signal duration indicates that there is no obstacle)
00023        echoTimeout.attach_us(this, &JSN_SR04::stopTimer, SENSOR_TIMEOUT);
00024 
00025          // Stop measurement and
00026        echo.fall(this, &JSN_SR04::stopTimer);
00027        echo.rise(NULL);
00028     }
00029 }
00030 
00031 void JSN_SR04::calculateDistance() {
00032     int timer_state;        // Current timer state (ticks amount)
00033 
00034     // Check if timer was even started
00035     if (timerStarted) {
00036         timer_state = timer.read();
00037 
00038         // If timeout occured (no obstacle)
00039         if (timer_state >= SENSOR_TIMEOUT) distance = -1;
00040 
00041         // If there is no timeout (an obstacle detected)
00042         else {
00043             // Calculate distance (duration of the signal * constant used in datasheet)
00044             distance = timer.read() * 1e6 / 58;
00045 
00046             // Set distance to the minimum if it's lower
00047             if (distance < minDistance)
00048                 distance = minDistance;
00049 
00050                 // Set distance to the maximum if it's higher
00051             if (distance > maxDistance)
00052                 distance = maxDistance;
00053         }
00054 
00055         // Indicate that new data is ready
00056         newDataReady = true;
00057      }
00058 }
00059 
00060 void JSN_SR04::stopTimer() {
00061     // Stop the timer
00062    timer.stop();
00063 
00064     // Call the calculation function
00065     calculateDistance();
00066 
00067     // Reset the timer
00068    timer.reset();
00069    timerStarted = false;
00070 
00071     // Switch off the timeout timer event
00072    echoTimeout.detach();
00073    echo.fall(NULL);
00074 }
00075 
00076 void JSN_SR04::turnOffTrigger() {
00077     // Switch off the trigger
00078    trigger = 0;
00079 }
00080 
00081 void JSN_SR04::startMeasurement() {
00082     // Trigger the sensor (by a signal described in the datasheet)
00083    trigger = 1;
00084    triggerTimeout.attach_us(this, &JSN_SR04::turnOffTrigger, 100); 
00085 
00086     // Start to measure a response
00087    echo.rise(this, &JSN_SR04::startTimer);
00088 
00089     // Outdate current response
00090    newDataReady = false;
00091 }
00092 
00093 float JSN_SR04::getDistance_cm() {
00094     // Indicate that the data was read
00095    newDataReady = false;
00096 
00097     // Return the data
00098    return distance;
00099 }
00100 
00101 float JSN_SR04::getDistance_mm() {
00102     // Indicate that the data was read
00103    newDataReady = false;
00104 
00105     // Return the data
00106     if (distance != -1)
00107         return distance * 10;
00108 
00109     else return distance;
00110 }
00111 
00112 bool JSN_SR04::isNewDataReady() {
00113     // Return the indicator
00114    return newDataReady;
00115 }
00116 
00117 void JSN_SR04::setRanges(float minRange, float maxRange) {
00118     // Set new boundaries that are in range of a sensors reading ability (datasheet)
00119     if (minRange < maxRange) {
00120         if (minRange >= 2 && minRange < 400) // bug from revs. 4 and 5 corrected
00121             minDistance = minRange;
00122         if (maxRange <= 400)
00123             maxDistance = maxRange;
00124     }
00125 }
00126 
00127 float JSN_SR04::getMinRange() {
00128     // Return a lower boundary
00129    return minDistance;
00130 }
00131 
00132 float JSN_SR04::getMaxRange() {
00133     // Return an upper boundary
00134    return maxDistance;
00135 }