Diff: main.cpp

Revision:

0:504353f35956

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Sun Jan 03 13:11:03 2010 +0000
@@ -0,0 +1,61 @@
+#include "mbed.h"
+
+Serial pc(USBTX,USBRX);
+
+DigitalInOut pingPin(p18);
+
+Timer tmr;
+
+long microsecondsToInches(long microseconds);
+long microsecondsToCentimeters(long microseconds);
+
+int main() {
+    while (1) {
+        // establish variables for duration of the ping,
+        // and the distance result in inches and centimeters:
+        long duration, inches, cm;
+
+        // The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
+        // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
+        pingPin.output();
+        pingPin = 0;
+        wait_us(2);
+        pingPin = 1;
+        wait_us(5);
+        pingPin = 0;
+
+        // The same pin is used to read the signal from the PING))): a HIGH
+        // pulse whose duration is the time (in microseconds) from the sending
+        // of the ping to the reception of its echo off of an object.
+        pingPin.input();
+
+        // pulseIn
+        while (!pingPin); // wait for high
+        tmr.start();
+        while (pingPin); // wait for low
+        duration = tmr.read_us();
+
+        // convert the time into a distance
+        inches = microsecondsToInches(duration);
+        cm = microsecondsToCentimeters(duration);
+
+        pc.printf("in=%4d, cm=%4d\n", inches, cm);
+        wait_ms(100);
+    }
+}
+
+long microsecondsToInches(long microseconds) {
+    // According to Parallax's datasheet for the PING))), there are
+    // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
+    // second).  This gives the distance travelled by the ping, outbound
+    // and return, so we divide by 2 to get the distance of the obstacle.
+    // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
+    return microseconds / 74 / 2;
+}
+
+long microsecondsToCentimeters(long microseconds) {
+    // The speed of sound is 340 m/s or 29 microseconds per centimeter.
+    // The ping travels out and back, so to find the distance of the
+    // object we take half of the distance travelled.
+    return microseconds / 29 / 2;
+}
\ No newline at end of file