© 1995 Microchip Technology Inc.

DS00597A-page 1

FIGURE 1:

RANGING MODULE INTERFACE

BINH

INIT

ECHO

TRANSMIT

POLAROID 6500 RANGING MODULE

RE1

RE0

CCP1

PIC16C74

TRANSDUCER

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:

• Auto focus cameras

• Motion detection

• Robotics guidance

• Proximity sensing

• 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:

• Microcontroller

• 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.

Author:

Robert Schreiber

Logic Products Division

THEORY OF OPERATION

Ultrasonic ranging entails transmitting a sound wave

and measuring the time that it takes for the sound wave

to reflect off of an object and back to the origin. The

reflection 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 configured as digital outputs and are

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

configured 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 configured for capture mode

(CCP1CON). Figure 2 shows the timing relationship for

Note:

The ranging module requires 5.0 millisec-

onds to stabilize during power-up.

AN597

Implementing Ultrasonic Ranging

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