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The electric drive systems used in industrial applications are

increasingly required to meet higher performance and reliabilityrequirements. The DC motor is an attractive piece of equipment in

many industrial applications requiring variable speed and load

characteristics due to its ease of controllability. Microcontrollers

provide a suitable means of meeting these needs. Certainty, part of

the recent activity on microcontrollers can be ascribed to theirnewness and challenge. In this paper, implementation of the

MC68HC11E9 microcontroller for speed control of DC motor fed by

a DC chopper has been investigated. The chopper is driven by a

high frequency PWM signal. Controlling the PWM duty cycle is

equivalent to controlling the motor terminal voltage, which in turn

adjusts directly the motor speed. Experimental results have been

obtained that show the employment of microcontroller for speed

control and over current protection of a DC motor.

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DC motor: has only a pair of + and leads.Connecting to a DC voltage source, DC motors move in one direction. Byreversing the voltage polarity, they will move in the opposite direction.

DC MotorsDC Motors

Figure 11.7 DC motor rotation

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DC Motors -DC Motors - Bidirectional controlBidirectional control (1/2)(1/2)

With the help of relays or some specially designed chips, the rotationaldirections (forward and backward) of DC motors can be control.

The basic concept is the H-Bridge control of DC motors

Figure 11.8 H-Bridge Motor Configuration Figure 11.9 H-Bridge Motor Clockwise Configuration

P1.0 =0

P1.3=0

P1.1 =1

P1.2 =1

P1.x : 0=on, 1=off

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Figure 11.10 H-Bridge MotorCounter-ClockwiseConfiguration

Figure 11.11 H-Bridge in an Invalid Configuration

H-Bridge control can be created using relays, transistors, or a single IC solution.

When using relays and transistors, make sure that invalid configuration do not occur.

DC Motors -DC Motors - Bidirectional controlBidirectional control (2/2)(2/2)

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DC Motors -DC Motors - Speed controlSpeed control by PWMby PWM (1/2)(1/2)

The speed of DC motor depends on three factors; (a) load, (b) voltage and (c) current

For a fixed load, speed of DC motor can be changed bypulse width modulation (PWM)

PWM is to change the width of the pulse applied to DC motor which lead to an increase or

decrease the amount of power supplied to the motor.

As a result, the motor speed increases or decreases respective to the power supplied.

Although the amplitude of the pulse is fixed at a voltage level, but its duty is varied.

The wider the pulse, the higher speed of motor.

Figure 11.12 Pulse Width Modulation Comparison

Moto

rSpeed

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DC Motors

Only One Winding

Two Connections: + and

Reversing Polarity Reverses Motor Move Continuously

Cannot Determine Position

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Characteristics:

RPM No Load: Maximum RPM With No Load on Shaft

Given in Data Sheets

Loaded: Actual Maximum When Loaded

Not in Most Data Sheets

Voltage Range Speed Increases With Voltage on a Given Motor

Current Draw

Data Sheet Rating Is With Nominal Voltage and No Load Increases With Load

Speed Decreases With Load

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DC Motor Rotation

(Permanent MagnetField)

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Bi-Directional Control

Can Change Polarity With a Little Work

H-Bridge Is Simplest Method

Uses Switches (Relays Will do)

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Controlling Speed

Speed Depends On Load

Voltage

Current

Can Control Power By Changing (Modulating)Width of Pulse to Motor

Wider Pulse Faster Speed

Narrower Pulse Slower Speed

Note: Doesnt Work With AC Motors AC Motor Speed Depends on AC Frequency (CPS)

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#include

sbit inr=P32; //speed increment switch

sbit dcr=P33; //speed decrement switch

main()

{unsigned char i=080; //i has initial speed value=half speed = 80H

P3=0ff; //configure P3 to accept switches

while(1)

{if (!inr) //if increment is pressed{while (!inr); //wait till key is released

if (i>10) //if speed is more than minimum

i=i-10; //increase the DC motor speed, by decreasing the count

} //end of if

if (!dcr) //if decrement is pressed

{while (!dcr); //wait till key is released

if (i

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Hex keypad

Placement of keys on port linesPlacement of keys on port lines Connection of Hex keypad to 8051Connection of Hex keypad to 8051

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#include

#include

#include"lcd.h"

unsigned char rows,columns,result;unsigned char temp = 0;

void delay() //delay subroutine

{unsigned int i;

for(i=0;i0x09)

{result += 0x37; //if value is greater than 9, add 37H

WriteChar(result);}else

{result += 0x30; //if value is between 0 to 9, add 30H

WriteChar(result);}

} //end of display subroutine

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void KeyScan() //Keypad subroutine

{again:columns = 0x0e; //make P1.0 low

rows = 0x04; //4 rows to check

result = 0x0; //Key value starts at 0next: P1 = columns; //output columns

CY = 1; //make CY = 1 for next rotation

columns = 1;

if(!CY)

{ClrLcd(); //key foundreturn;}

else

{result += 1; //next column; key value is incremented

goto rot;}}

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else

{result += 0x04; //for next row; 4 is added to key value

rows - -; //decrement number of rows

if(rows = = 0)

goto again; //start from beginningelse

{goto next; }

}}

void main(){P0 = 0xff; //make as input port

P1 = 0x00;

InitLcd(); //initialize LCD

WriteString("KEY PRESSED=")

while(1)

{KeyScan(); //call keypad subroutine

WriteString("KEY PRESSED=")

Display(); //display the value

} }

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ELEVATOR INTERFACE TO 8051ELEVATOR INTERFACE TO 8051

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#i l d 1 d2

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#include

void delay(unsigned int);

main()

{unsigned char Flr[9] = {0xff,0x00,0x03,0xff,0x06,0xff,0xff,0xff,0x09}

unsigned char ReqFlr,CurFlr = 0x01,i,j;P0 = 0x00;

P0 = 0xf0;

while(1)

{P1 = 0x0f;ReqFlr = P1|0xf0;

while(ReqFlr == 0xff)

ReqFlr = P1|0xf0; //Read Request Floor from P1

ReqFlr = ~ ReqFlr;

if(CurFlr == ReqFlr) //If request floor is equal to current floor

{P0 = Flr[CurFlr]; //Clear Floor Indicator

P0 = P0|0xf0; //Enable again

continue; //Go up to read again

}

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else if (CurFlr > ReqFlr) //If current floor is > request floor

{

i = Flr[CurFlr] - Flr[ReqFlr]; //Get the no of floors to travel

j = Flr[CurFlr];for(; i>0; i- -) //Move the indicator down

{P0 = 0x0f0 | j;

j- -;

delay(25000);

}}

else //If Current floor is < request floor

{i = Flr[ReqFlr] - Flr[CurFlr]; //Get the no of floors to travel

j = Flr[CurFlr];

for(; i>0; i- -) //Move the indicator Up{P0=0f0 | j;

j++;

delay(25000);

}}

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CurFlr = ReqFlr; //Update current floor

P0 = Flr[CurFlr]; //Clear the request indicator

P0 = P0|0xf0;

} //end of while} //end of main

void delay(unsigned int x)

{for(; x>0; x- -);}

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What is PWM

Pulse-width modulation (PWM), orpulse-duration modulation

(PDM), is a commonly used technique forcontrolling power to inertial electricaldevices, made practical by modern

electronic power switches. The average value of voltage (and current)

fed to the load is controlled by turning theswitch between supply and load on and off

at a fast pace. The longer the switch is oncompared to the off periods, the higher thepower supplied to the load is.

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What is PWM

The PWM switching frequency has to bemuch faster than what would affect theload, which is to say the device that usesthe power. Typically switchings have to bedone several times a minute in an electricstove, 120 Hz in a lamp dimmer, from fewkilohertz (kHz) to tens of kHz for a motordrive and well into the tens or hundreds ofkHz in audio amplifiers and computerpower supplies.

http://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Hertz

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What is PWM

The main advantage of PWM is that powerloss in the switching devices is very low. Whena switch is off there is practically no current,and when it is on, there is almost no voltagedrop across the switch. Power loss, being theproduct of voltage and current, is thus in bothcases close to zero. PWM also works well with

digital controls, which, because of their on/offnature, can easily set the needed duty cycle.

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Controlling Motor DirectionControlling Motor Direction

To change the direction of rotation:

Simply switch the polarity of the battery leads

going to the motor (that is, switch the + and

battery leads)

+

-

-

+

CW CCW

Direction of

Rotation

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Inside a Toy MotorInside a Toy Motor

(Similar to TekBot Motor)(Similar to TekBot Motor)