Matthew Shoemaker
main.cpp@0:504353f35956, 2010-01-03 (annotated)
- Committer:
- mshoemaker
- Date:
- Sun Jan 03 13:11:03 2010 +0000
- Revision:
- 0:504353f35956
Who changed what in which revision?
| User | Revision | Line number | New contents of line |
|---|---|---|---|
| mshoemaker | 0:504353f35956 | 1 | #include "mbed.h" |
| mshoemaker | 0:504353f35956 | 2 | |
| mshoemaker | 0:504353f35956 | 3 | Serial pc(USBTX,USBRX); |
| mshoemaker | 0:504353f35956 | 4 | |
| mshoemaker | 0:504353f35956 | 5 | DigitalInOut pingPin(p18); |
| mshoemaker | 0:504353f35956 | 6 | |
| mshoemaker | 0:504353f35956 | 7 | Timer tmr; |
| mshoemaker | 0:504353f35956 | 8 | |
| mshoemaker | 0:504353f35956 | 9 | long microsecondsToInches(long microseconds); |
| mshoemaker | 0:504353f35956 | 10 | long microsecondsToCentimeters(long microseconds); |
| mshoemaker | 0:504353f35956 | 11 | |
| mshoemaker | 0:504353f35956 | 12 | int main() { |
| mshoemaker | 0:504353f35956 | 13 | while (1) { |
| mshoemaker | 0:504353f35956 | 14 | // establish variables for duration of the ping, |
| mshoemaker | 0:504353f35956 | 15 | // and the distance result in inches and centimeters: |
| mshoemaker | 0:504353f35956 | 16 | long duration, inches, cm; |
| mshoemaker | 0:504353f35956 | 17 | |
| mshoemaker | 0:504353f35956 | 18 | // The PING))) is triggered by a HIGH pulse of 2 or more microseconds. |
| mshoemaker | 0:504353f35956 | 19 | // Give a short LOW pulse beforehand to ensure a clean HIGH pulse: |
| mshoemaker | 0:504353f35956 | 20 | pingPin.output(); |
| mshoemaker | 0:504353f35956 | 21 | pingPin = 0; |
| mshoemaker | 0:504353f35956 | 22 | wait_us(2); |
| mshoemaker | 0:504353f35956 | 23 | pingPin = 1; |
| mshoemaker | 0:504353f35956 | 24 | wait_us(5); |
| mshoemaker | 0:504353f35956 | 25 | pingPin = 0; |
| mshoemaker | 0:504353f35956 | 26 | |
| mshoemaker | 0:504353f35956 | 27 | // The same pin is used to read the signal from the PING))): a HIGH |
| mshoemaker | 0:504353f35956 | 28 | // pulse whose duration is the time (in microseconds) from the sending |
| mshoemaker | 0:504353f35956 | 29 | // of the ping to the reception of its echo off of an object. |
| mshoemaker | 0:504353f35956 | 30 | pingPin.input(); |
| mshoemaker | 0:504353f35956 | 31 | |
| mshoemaker | 0:504353f35956 | 32 | // pulseIn |
| mshoemaker | 0:504353f35956 | 33 | while (!pingPin); // wait for high |
| mshoemaker | 0:504353f35956 | 34 | tmr.start(); |
| mshoemaker | 0:504353f35956 | 35 | while (pingPin); // wait for low |
| mshoemaker | 0:504353f35956 | 36 | duration = tmr.read_us(); |
| mshoemaker | 0:504353f35956 | 37 | |
| mshoemaker | 0:504353f35956 | 38 | // convert the time into a distance |
| mshoemaker | 0:504353f35956 | 39 | inches = microsecondsToInches(duration); |
| mshoemaker | 0:504353f35956 | 40 | cm = microsecondsToCentimeters(duration); |
| mshoemaker | 0:504353f35956 | 41 | |
| mshoemaker | 0:504353f35956 | 42 | pc.printf("in=%4d, cm=%4d\n", inches, cm); |
| mshoemaker | 0:504353f35956 | 43 | wait_ms(100); |
| mshoemaker | 0:504353f35956 | 44 | } |
| mshoemaker | 0:504353f35956 | 45 | } |
| mshoemaker | 0:504353f35956 | 46 | |
| mshoemaker | 0:504353f35956 | 47 | long microsecondsToInches(long microseconds) { |
| mshoemaker | 0:504353f35956 | 48 | // According to Parallax's datasheet for the PING))), there are |
| mshoemaker | 0:504353f35956 | 49 | // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per |
| mshoemaker | 0:504353f35956 | 50 | // second). This gives the distance travelled by the ping, outbound |
| mshoemaker | 0:504353f35956 | 51 | // and return, so we divide by 2 to get the distance of the obstacle. |
| mshoemaker | 0:504353f35956 | 52 | // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf |
| mshoemaker | 0:504353f35956 | 53 | return microseconds / 74 / 2; |
| mshoemaker | 0:504353f35956 | 54 | } |
| mshoemaker | 0:504353f35956 | 55 | |
| mshoemaker | 0:504353f35956 | 56 | long microsecondsToCentimeters(long microseconds) { |
| mshoemaker | 0:504353f35956 | 57 | // The speed of sound is 340 m/s or 29 microseconds per centimeter. |
| mshoemaker | 0:504353f35956 | 58 | // The ping travels out and back, so to find the distance of the |
| mshoemaker | 0:504353f35956 | 59 | // object we take half of the distance travelled. |
| mshoemaker | 0:504353f35956 | 60 | return microseconds / 29 / 2; |
| mshoemaker | 0:504353f35956 | 61 | } |