AN597 Datasheet, PDF(1/8 Page) Microchip Technology – Implementing Ultrasonic Ranging

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AN597 Datasheet, PDF (1/8 Pages) Microchip Technology – Implementing Ultrasonic Ranging

AN597

Implementing Ultrasonic Ranging

Author:

Robert Schreiber

Logic Products Division

INTRODUCTION

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:

â¢ Auto focus cameras

â¢ Motion detection

â¢ Robotics guidance

â¢ Proximity sensing

â¢ 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:

â¢ Microcontroller

â¢ Polaroid 6500 Ranging Module

The microcontroller performs the intelligence and

arithmetic functions for ultrasonic ranging, while the

Polaroid 6500 Ranging Module performs the ultrasonic

signal transmissions and echo detection.

FIGURE 1: RANGING MODULE INTERFACE

THEORY OF OPERATION

Ultrasonic ranging entails transmitting a sound wave

and measuring the time that it takes for the sound wave

to reï¬ect off of an object and back to the origin. The

reï¬ection time is proportional to the distance that the

object is from the source. In this implementation, the

sound wave is transmitted and received from the same

transducer. Therefore, a blanking interval is required

between signal transmission and reception to eliminate

false echoes (i.e., a transmitted signal being detected

as its own echo).

CIRCUIT CONFIGURATION

In this implementation, a PIC16C74 is connected to the

ranging module as shown in Figure 1. The RE0 and

RE1 I/O pins are conï¬gured as digital outputs and are

tied to INIT and BINH, respectively. The CCP1 pin is

conï¬gured as a digital input and is tied to ECHO

through a pull-up resistor. The pull-up resistor is

needed since the ECHO signal is an open-collector

output. The CCP1 pin is conï¬gured for capture mode

(CCP1CON). Figure 2 shows the timing relationship for

VDD and the three signal lines (INIT, BINH, and ECHO).

Note: The ranging module requires 5.0 millisec-

onds to stabilize during power-up.

RE1

RE0

CCP1

PIC16C74

BINH

INIT

TRANSMIT

ECHO

POLAROID 6500 RANGING MODULE

TRANSDUCER

Thi d

t d ith F M k 4 0 4

DS00597A-page 1

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