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Date: Mon, 02 Dec 1996 14:59:34 GMTServer: NCSA/1.4.2Content-type: text/html<html><head><title>CSE477 Laboratory Assignment #3</title></head><h1>CSE477: Digital Systems Design</h1><h3>Steve Burns, Spring 1996 </h3><hr><h2>Lab 1</h3><p><h3>Motors, Motor Driver Circuits, Optical Speed Sensors, and Feedback</h3><p><b>Distributed: April 22 - Complete By: May 2</b><hr><p><H3>Objectives</H3>When you have completed this lab, you should know how to:<UL><LI>Run a DC motor using an H-bridge motor driver circuit and a duty-cyclespeed adjustment.<LI>Determine the speed of a motor shaft using an optical sensor,<LI>Integrate the two systems so that a motor can be run at a predeterminedspeed under a variety of loading conditions.</UL> <H3>Part 1: Setting Up the Motors and Optical Speed Sensors</H3>You will need to fabricate a disk with black and white strips to be usedin conjunction with the optical sensors to determine the speed at which themotor shaft is spinning. I've xeroxed enlarged copies of the disks shown onpage 124 of the Mobile Robots Text. Cut out the one with 16 black stripesand paste it (using a glue stick) to a piece of foam board. Cut outthe combination. Punch a hole in the center using the sharp end of apair of scissors (be careful not to cut yourself) so that the disk pressurefits onto the pully shaft of the motor.<p>You will also need to attach the motor and the sensor together. Scotchtape works well for this. Before you do this though, acquire a sense forhow close the sensor needs to be to the spinning disk for it to obtain agood signal. You can do this by wiring up the sensor: the blue andwhite leads correspond to the anode and cathode, respectively,of the transmiting LED, and the green and purple leads correspond to the collectorand emitter of the receiving phototransistor, respectively.No more than 20 mA should be allowed to flow through the LED. With a 5 voltsupply, an 180 ohm series resistor works well. On the receiving end, a6.8 kiloohm series resistor will make an excellent voltage divider convertingthe current change caused to the presense or absense of a reflecting surfaceinto a voltage change interpretable at CMOS digital levels. To determine howclose the sensor has to be to a reflecting surface, measure the voltage changesbetween the resistor/phototransistor connection and ground as the distancebetween the sensor and the surface varies. I found that the sensor had to bebe about 1/20 of a inch from the surface. Your sensor and circuit might beslightly different.<p>To drive the motor, use the L293D bipolar driver chip. Please note theunusual pinout. There are fouroutput buffers on this chip, so there is enough circuitry for 2 H-Bridges.To vary the speed of the motor, vary the duty-cycle of the enable signal.A larger duty-cycle will result in a higher average voltage and thus ahigher motor speed. Experiment with different duty-cycles and determinethe maximum/minumum no-load speeds of the motor. <H3>Part 2: Connecting the Speed Sensors to the Motors Using Feedback</H3>Since the speed of a motor depends not only on the applied voltage but alsoon the amount of load, feedback from speed sensors is necessaryto accurately control the speed of your motor. Your are to devise a systemto control the speed of your motors using the optical speed sensors asinput and a variation in duty-cycle as output. More on this later.<H3>Part 3: Operate Two Motors Simultaneously</H3>Modify your microcontroller program to control two motors simultaneously.Make sure that both motors have individual speed sensors. <H3>What to Turn In</H3>Demo the two motors spinning in lockstepat three different rates to the TAs.</body><address><hr>burns@cs.washington.edu</address><p></html>⌨️ 快捷键说明
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