EBB Notes 1
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Rachel & Mike, March 29(?)
Some functional if rough arduino code for a Parallax Ping))) module has been produced. It blinks an LED once per half second, with a larger duty cycle the closer an object is to the sensor. The Ping))) module is large and somewhat cumbersome, and appears to be quite inaccurate at distances greater than about 2-3 feet. There is a pair of MaxSonar-EZ1 modules in the Cyborg parts bin which look interesting to try as well.
Code:
/* * Based on code found at http://arduino.cc/en/Tutorial/Ping */ int pin = 13; int pingPin = 12; int ledPin = 11; double periodFactor = .5; // percent of one second void setup() // run once, when the sketch starts { // pinMode(pin, OUTPUT); // sets the digital pin as output Serial.begin(9600); pinMode(ledPin, OUTPUT); } void loop() // run over and over again { long duration, inches, cm; // The PING))) is triggered by a HIGH pulse of 2 or more microseconds. // We give a short LOW pulse beforehand to ensure a clean HIGH pulse. pinMode(pingPin, OUTPUT); digitalWrite(pingPin, LOW); delayMicroseconds(2); digitalWrite(pingPin, HIGH); delayMicroseconds(5); digitalWrite(pingPin, LOW); delayMicroseconds(2); // 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. pinMode(pingPin, INPUT); duration = pulseIn(pingPin, HIGH); // convert the time into a distance inches = microsecondsToInches(duration); cm = microsecondsToCentimeters(duration); Serial.print(inches); Serial.print("in, "); Serial.print(cm); Serial.print("cm"); Serial.println(); pwm(duration); } void pwm(long microseconds) { Serial.print(microseconds); Serial.println("ms"); long offCycle = microseconds / 18; long onCycle = 1000 - offCycle; digitalWrite(ledPin, HIGH); delay(onCycle * periodFactor); digitalWrite(ledPin, LOW); delay(offCycle * periodFactor); } 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; }