1. PING))) Ultrasonic Distance Sensor living with the lab ultrasonic pressure waves from PING))) speaker The PING))) sensor emits short bursts of sound and listens for this sound to echo off of nearby objects. The frequency of the sound is too high for humans to hear (it is ultrasonic). The PING))) sensor measures the time of flight of the sound burst. A user then computes the distance to an object using this time of flight and the speed of sound (1,126 ft/s). sound wave reflects off object and returns to PING))) “microphone”

2. living with the lab 2 Computing Distance

3. living with the lab 3 measurement range: 0.8 in to 120 inches supply voltage: 5V supply current: 30mA Specifications www.parallax.com/Portals/0/Downloads/docs/prod/acc/28015-PING-v1.6.pdf sensing distance (feet) as a function of angle

4. living with the lab 4 AREF GND 13 12 PMW 11 PMW 10 PMW 9 8 7 PMW 6 PMW 5 4 PMW 3 2 TX 1 RX 0 RESET 3V3 5V GND GND Vin 0 1 2 3 4 5 DIGITAL ANALOGPOWER Connection to an Arduino

5. living with the lab 5 Arduino Sketch void setup() { Serial.begin(9600); } void loop() { long duration, inches; pinMode(7, OUTPUT); // send a 5 microsecond pulse out pin 7 digitalWrite(7, LOW); delayMicroseconds(2); digitalWrite(7, HIGH); delayMicroseconds(5); digitalWrite(7, LOW); pinMode(7, INPUT); // make pin 7 an input duration = pulseIn(7, HIGH); // measure the time of flight of sound wave inches = duration / 74 / 2; // 1130 ft/s * 12in/ft * 1s/1,000,000us = 74 // factor of 2 since sound travels out and back Serial.print(inches); // display distance in inches Serial.print("in "); Serial.println(); } The Arduino triggers the PING))) by sending a 5ms pulse to the sensor through pin 7, which is initially configured as an Arduino OUTPUT. Immediately after sending this pulse, pin 7 is switched to an INPUT. When the PING))) receives the 5ms pulse from the Arduino, it sends a 40kHz (ultrasonic) burst of sound out its “speaker” and sets pin 7 to HIGH. The PING))) then waits for the sound burst to reflect off of something and return to the “microphone” where it is detected; the PING))) then sets pin 7 to LOW. The Arduino uses the pulseIn command to measure the time of flight of the sound wave in microseconds (the time that pin 7, when configured as an input, is HIGH). The “time of flight” of the sound wave in ms is stored in the variable “duration.”

6. living with the lab 6 Example Application void setup() {pinMode(8, OUTPUT); } void loop() { long duration, inches, tone_freq; pinMode(7, OUTPUT); // make pin 7 an output digitalWrite(7, LOW); // send wakeup pulse delayMicroseconds(2); digitalWrite(7, HIGH); delayMicroseconds(5); digitalWrite(7, LOW); pinMode(7, INPUT); // make pin 7 an input duration = pulseIn(7, HIGH); // time of flight of wave inches = duration / 74 / 2; // compute distance in inches tone_freq = inches*100; // a freq of 100*inches is good tone(8,tone_freq); // send a tone out of pin 8 } The picture shows how stiff wire (such as a coat hanger) can be used to mount the PING))) to an aluminum plate. An Arduino and breadboard are also mounted to the plate, and a piezospeaker is installed on the breadboard to allow the device to output an irritating noise whose frequency is proportional to the distance from the PING))) to a target.