Matthew Shoemaker
/
PingRangeFinder
main.cpp
- Committer:
- mshoemaker
- Date:
- 2010-01-03
- Revision:
- 0:504353f35956
File content as of revision 0:504353f35956:
#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; }