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Chapter 1: Detect Distance with the Ping))) Ultrasonic Detector · Page 1

Chapter #1: Detect Distance with the Ping)))

(TM)

Ultrasonic Sensor

WHAT IS THE PING))) SENSOR?

The Ping))) sensor is a device you can use with the BASIC Stamp to measure how far

away an object is. With a range of 3 centimeters to 3.3 meters, it's a shoe-in for any

number of robotics and automation projects. It's also remarkably accurate, easily

detecting an object's distance down to the half centimeter.

Figure 1

The Ping))) Sensor

HOW DOES THE PING))) SENSOR WORK?

Figure 2 shows how the Ping))) sensor sends a brief chirp with its ultrasonic speaker and

makes it possible for the BASIC Stamp to measure the time it takes the echo to return to

its ultrasonic microphone. The BASIC Stamp starts by sending the Ping))) sensor a pulse

to start the measurement. Then, the Ping))) sensor waits long enough for the BASIC

Stamp program to start a

PULSIN command. At the same time the Ping))) sensor chirps

its 40 kHz tone, it sends a high signal to the BASIC Stamp. When the Ping))) sensor

detects the echo with its ultrasonic microphone, it changes that high signal back to low.

The BASIC Stamp's

PULSIN command stores how long the high signal from the Ping)))

sensor lasted in a variable. The time measurement is how long it took sound to travel to

the object and back. With this measurement, you can then use the speed of sound in air

to make your program calculate the object's distance in centimeters, inches, feet, etc...

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The draft material in this Chapter is part of a forthcoming Stamps in Class text by Andy Lindsay.

Summary of content (5 pages)

PAGE 1
Chapter 1: Detect Distance with the Ping))) Ultrasonic Detector · Page 1 Chapter #1: Detect Distance with the Ping)))(TM) Ultrasonic Sensor WHAT IS THE PING))) SENSOR? The Ping))) sensor is a device you can use with the BASIC Stamp to measure how far away an object is. With a range of 3 centimeters to 3.3 meters, it's a shoe-in for any number of robotics and automation projects. It's also remarkably accurate, easily detecting an object's distance down to the half centimeter.
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Page 2 · Smart Sensors and Applications Figure 2 - How the Ping))) Sensor Works The Ping))) sensor's chirps are not audible because 40 kHz is ultrasonic. What we consider sound is our inner ear's ability to detect the variations in air pressure caused by vibration. The rate of these variations determines the pitch of the tone. Higher frequency tones result in higher pitch sounds and lower frequency tones result in lower pitch tones.
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Chapter 1: Detect Distance with the Ping))) Ultrasonic Detector · Page 3 Ping))) Sensor Circuit Figure 3 shows a schematic and wiring diagram you can use to test the Ping))) sensor. √ Build the circuit. Figure 3 - Ping))) Sensor Schematic and Wiring Diagram Testing the Ping))) Sensor As mentioned earlier, the Ping))) sensor needs a start pulse from the BASIC Stamp to start its measurement.
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Page 4 · Smart Sensors and Applications √ √ √ √ √ √ Place an object (like a water bottle, box, or paper target) 15 cm from the front of the Ping))) sensor. Enter, save, and run PingTest.bs2. The Debug Terminal should start reporting a value in the neighborhood of 450. Values of 438 to 466 mean the distance is between 15 and 16 cm. Move the target to a distance of 30 cm from the Ping))) sensor and verify that the value of the time variable doubled.
PAGE 5
Chapter 1: Detect Distance with the Ping))) Ultrasonic Detector · Page 5 √ √ Save PingTest.bs2 as PingCentimeters.bs2. Add the two new lines of code to the program's DO...LOOP between the DEBUG and PAUSE commands. When you're done, the DO...