A Guide for Online Information About:

UltraSonic Ranging

by Rick Prescott

Let me begin by discussing some of the pertinent details of what an Ultrasonic Ranging System is and its basic principal of operation. Ultrasonic is a word meaning essentially "high frequency sound," applying to sounds that are just above the range of human hearing. The Ultrasonic frequency range is typically considered to be 20 to 500 KHz, or just below the AM Broadcast band. Sounds at these frequencies are much more directional than lower frequency sounds. The higher the frequency, the more focused the sound.

Sound travels at approximately 1065 feet/s at sea level. The actual speed will vary depending on actual altitude, humidity, and barometric pressure. An Ultrasonic Ranging System allows the measurement of distance between two points by taking advantage of these two facts. It operates simply by emitting a short burst of high frequency sound and then listening for an echo. When an echo is received, the distance can be computed by dividing the time measured between the emission and reception by 2. This division is necessary to take into account the time the sound travels towards an object from the transmitter and the time the reflected sound takes to travel from the object back to the receiver. Homebrew Sonar Ranging System by John Whitten, Jr.

What is an Ultrasonic Ranging System? An Ultrasonic Ranging System is a unit that detects the presence of an object and calculates the distance to that object. This is accomplished by transmitting an ultrasonic (high frequency) sound. This sound is above the range of normal human hearing. Sound travels at a known speed and when the sound strikes an object it is reflected back to the source. This reflected sound is called the "echo." All that is required to calculate the distance to an object is to measure the time between the transmitting of the sound and the return echo. Sound travels at the rate of 1' every 0.0009 s. Therefore, an object 10' away from the transmitter would take approximately 0.018 s to detect (2 × 10 × 0.0009). Notice that the 10' was multiplied by 2. The sound actually travels 20'—10' out to the object and 10' back as the echo.

EXAMPLE PROJECTS

Sonar Ranging
This project describes how to reuse ultrasonic transducers and electronics taken from a Polaroid 670AF instant camera as sonar distance ranging sensors. The documentation also describes the difference between the board taken from the camera and a board that can be bought at robot supply stores (Polaroid series 6500 module). In this example, the ranging module is controlled by a MCU compatible to the MCS-51 series. The circuit described herein could be connected to other MCUs/CPUs as well.

Polaroid 6500 Series Sonar Ranging Module PID #615077
The 6500 Series is an economical sonar ranging module that can drive all Polaroid electrostatic transducers without additional interface. This module, with a simple interface, is able to measure distances from 6" to 35'. The typical absolute accuracy is ý 1% of the reading over the entire range.

The Minibot's Sonar Sensors by Kam Leang (1999)

Error Eliminating Rapid Ultrasonic Firing—A PDF file describing high-tech, expensive Ultrasonic Robot navigation designed for a fire fighting robot.

Gadget - Machine Intelligence Platform with an Ultrasonic ranging system included.

YO! Guide Your Vehicle
The Yo! Guided Vehicle (YGV) follows a wire that may be buried in the floor or simply taped to the floor surface. The YGV Track Controller generates the signal carried by the wire.

Ultrasonic Ranging in the Undergraduate Laboratory
Scott Goodchild, 1994 Supervisor: E. Sternin: "There are many experiments in an undergraduate mechanics lab where a compact ranging system can be of great benefit. The Ultrasonic Ranging System (URS) developed by Polaroid to automatically focus cameras is ideally suited to such applications. The system is composed of an electrostatic transducer, which acts as both transmitter and receiver, and a single electronic module containing the drive, receiving, and processing circuitry. To determine the distance to an object, the interval time between the transmitted ultrasonic pulse and the received echo from the object is measured With an appropriate clock rate, a resolution of approximately 1mm can be obtained."

Interfacing the the Polaroid Sonar Units to the BSII—A complete application note. You will also find some more general info on using the 6500 Boards.

AN597 - Implementing Ultrasonic Ranging
Object ranging is essential in many types of systems. One of the most popular ranging techniques is ultrasonic ranging. Ultrasonic ranging is used in a wide variety of applications including auto focus cameras, motion detection, robotics guidance, proximity sensing, and object ranging. This application note describes a method of interfacing PIC16Cxx microcontrollers to the Polaroid 6500 Ranging Module. This implementation uses a minimum of microcontroller resources, a CCP module, and two I/O pins. The two major components of the system are the microcontroller and the Polaroid 6500 Ranging Module. The microcontroller performs the intelligence and arithmetic functions for ultrasonic ranging, and the Polaroid 6500 Ranging Module performs the ultrasonic signal transmissions and echo detection.

An Ultrasonic Ranging System for the Blind
In this design project, a mobile ultrasonic ranging system was developed for the blind.

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