09 chapter 8 - human physical interface

7/31/2019 09 Chapter 8 - Human Physical Interface

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Chapter8

Sections1 9

Dr.IyadJafar

TheHuman

and

Physical

Interface


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Outline

Introduction

From

Switches

to

Keypads LEDDisplays

SimpleSensors

Actuators

Summary

2


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Introduction

Humansneedto

interfacewith

embeddedsystems;

inputdataandseeresponse

Inputdevices:switches,

pushbuttons,keypads,sensors

Outputdevices:LEDs,

sevensegmentdisplays,liquidcrystaldisplays,

motors,actuators

3

EmbeddedComputer

Hardware

Software

Input

Variables

Output

Variables

Linktoother

systems

UserInteraction


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Introduction Examples

FridgeControlPanel

PhotocopierControl4


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Introduction

Examples

CarDashboard

5


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MovingFromSwitchestoKeypads

Switchesaregoodforconveyinginformationofdigitalnature

Theycanbeusedinmultiples;eachconnectedtooneportpin

Incomplexsystems,itmightnotbefeasibletokeepadding

switches?! Usekeypads!

Canbeusedtoconveyalphanumericvalues

Agroupofswitchesarrangedinmatrixform

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InternalStructureofKeypad

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Howto

Determine

the

Pressed

Key

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UsingKeypad

in

aMicrocontroller

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Example

Aprogramtoreadaninputfroma4x3keypadanddisplaysthe

equivalentdecimalnumberon4LEDs.Ifthepressedkeyisnot

anumber,

then

the

LEDs

should

be

all

on.

ThekeypadwillbeconnectedtoMCasfollows

Rows0to3connectedtoRB7toRB4respectively.

Columns0to2connectedtoRB3toRB1

UseportBchangeinterrupt

connecttheLEDstoRA0RA3

basedonthepressedkey,converttherowandcolumnvaluesto

binaryusingalookuptable

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KeypadInterfacingExample#INCLUDE PIC16F84A.INC

ROW_INDEX EQU 0X20COL_INDEX EQU 0X21

ORG 0X0000

GOTO START

ORG 0X0004GOTO ISR

START BSF STATUS,RP0

MOVLW B11110000

MOVWF TRISB ;SETRB1RB3ASOUTPUTAND;RB4RB7ASINPUT

MOVLW B00000000

MOVWF TRISA ;SETRA0RA3ASOUTPUT

BCF STATUS,RP0

CLRF PORTB ;INITIALIZEPORTBTOZERO

MOVF PORTB,W ;CLEARRBIFFLAG

BCF INTCON,RBIF

BSF INTCON,

RBIEBSF INTCON,GIE ;ENABLEPORTbCHANGEINTERRUPT

LOOP GOTO LOOP ;WAITFORPRESSEDKEY11


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KeypadInterfacingExampleISR MOVF PORTB,W ;READROWNUMBER

MOVWF ROW_INDEX

BSF STATUS,RP0 ;READCOLUMNNUMBER

MOVLW B00001110

MOVWF TRISB

BCF STATUS,RP0CLRF PORTB

MOVF PORTB,W

MOVWF COL_INDEX

CALL CONVERT ;CONVERTHEROWANDCOLUMN

RST_PB_DIRC BSF STATUS,RP0 ;PUTTHEPORTBACKTOINITIALSETTINGS

MOVLW B11110000

MOVWF TRISB ;SETRB1RB3ASOUTPUTAND

MOVLW B00000000 ;RB4RB7ASINPUT


BCF STATUS,RP0

CLRF PORTB

MOVF PORTB,W ;REQUIREDTOCLEARRBIFFLAG

BCF INTCON,RBIFRETFIE

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KeypadInterfacingExample

CONVERT BTFSS COL_INDEX,3 ; IF 1ST COLUMN,COL_INDEX=0MOVLW 0

BTFSS COL_INDEX,2; IF2ND COLUMN,COL_INDEX=1

MOVLW 1

BTFSS COL_INDEX,1;

IF3

RD

COLUMN,COL_INDEX=2

MOVLW 2

MOVWF COL_INDEX ; STORETHECOLUMNINDEX

FIND_ROW BTFSS ROW_INDEX,7 ; IF 1ST ROW,ROW_INDEX=0

MOVLW 0

BTFSS ROW_INDEX,6 ; IF 2ND ROW,ROW_INDEX=1

MOVLW 1

BTFSS ROW_INDEX,5 ; IF 3RD ROW,ROW_INDEX=2

MOVLW 2

BTFSS ROW_INDEX,4; IF 4TH ROW,ROW_INDEX=3

MOVLW 3

MOVWF ROW_INDEX

; CONTINUEDONNEXTPAGE13


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COMPUTE_VALUE MOVF ROW_INDEX,W ; KEY#=ROW_INDEX*3+COL_INDEX

ADDWF ROW_INDEX,W

ADDWF ROW_INDEX,W

ADDWF COL_INDEX,W ;THEVALUEISINW

CALL TABLE

MOVWF PORTA ;DISPLAYTHENUMBERONPORTA

RETURN

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TABLE ADDWF PCL,F

RETLW 0X01

RETLW 0X02

RETLW 0X03RETLW 0X04

RETLW 0X05

RETLW 0X06

RETLW 0X07

RETLW 0X08

RETLW 0X09

RETLW 0X0F ;ERRORCODE

RETLW 0X00

RETLW 0X0F ;ERRORCODE

END

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LEDDisplays

Lightemittingdiodesaresimpleandeffectiveinconveyinginformation

However,incomplex

systems

itbecomes

hard

to

deal

with

individualLEDs

Alternatives Sevensegmentdisplays

Bargraph

Dotmatrix

Starburst

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SevenSegmentDisplay

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SevenSegmentDisplay

Multiplexingof

seven

segment

digits

18

Connection PortBit

Segment a RB7

Segment b RB6

Segment c RB5

Segment d RB4

Segment e RB3

Segment f RB2

Segment g RB1

Segment dp RB0

Digit1drive RA0

Digit2drive RA1

Digit3drive RA2

Digit4drive RA3


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SevenSegmentDisplay

Multiplexingof

seven

segment

digits

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SevenSegmentDisplay

Example

Aprogramtocountcontinuouslythenumbers0through99

anddisplaythemontwosevensegmentdisplays.Thecount

shouldbe

incremented

every

1sec.

Oscillator

frequency

is

3

MHz.

connectthesevensegmentinputsa throughg toRB0throughRB6

respectively

connectthegatesofthecontrollingtransistorstoRA0(LSD)andRA1

(MSD) themainprogramwillberesponsiblefordisplayandmultiplexing

every5ms

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SevenSegmentDisplayExample

#INCLUDE PICF84A.INCLOW_DIGIT EQU 0X20

HIGH_DIGIT EQU 0X21

COUNT EQU 0X22

ORG

0X0000GOTO START

ORG 0X0004

ISR GOTO ISR

START BSF STATUS,RP0

MOVLW B00000000 ;setportBasoutput

MOVWF TRISB

MOVLW B0000000


BCF STATUS,RP0

CLRF PORTB

CLRF PORTA

CLRF LOW_DIGIT ;CLEARTHECOUNTVALUE

CLRF HIGH_DIGIT

CLRF COUNT21


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DISPLAY BCF STATUS,RP0MOVF LOW_DIGIT,W ;DISPLAYLOWERDIGIT

CALL TABLE ;GETTHESEVENSEGMENTCODE

MOVWF PORTB

BCF PORTA,1 ;enabledigit0

BSF PORTA,0

CALL DELAY_5MS ;KEEPITONFOR5MS

MOVF HIGH_DIGIT,W ;DISPLAY HIGHDIGIT

CALL TABLE ;GETTHESEVENSEGMENTCODE

MOVWF PORTBBCF PORTA,0

BSF PORTA,1

CALL DELAY_5MS ;KEEPITONFOR5MS

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SevenSegmentDisplayExample;CHECKIF 1SECELAPSED

INCF COUNT,F ;INCREMENTTHECOUNTVALUEIFTRUE

MOVF COUNT,W

SUBLW D100

BTFSS STATUS,Z

GOTO DISPLAY ;DISPLAYTHESAMECOUNT

INCF LOW_DIGIT,F ;INCREMENTLOWDIGITANDCHECKIF>9

MOVF LOW_DIGIT,W

SUBLW 0X0ABTFSS STATUS,Z

GOTO DISPLAY

CLRF LOW_DIGIT

INCF HIGH_DIGIT,F;INCREMENTHIGHDIGITANDCHECKIF>9

MOVF HIGH_DIGIT,W

SUBLW 0X0A

BTFSS STATUS,Z

GOTO DISPLAY

CLRF HIGH_DIGIT

GOTO DISPLAY23


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DELAY_5MS MOVLW D250

MOVWF 0X40

REPEAT NOP

NOP

NOP

NOP

NOP

NOP

NOP

NOP

NOP

NOP

NOPNOP

DECFSZ 0X40,1

GOTO REPEAT

RETURN

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TABLE ADDWF PCL, 1

RETLW B'00111111' ;'0'

RETLW B'00000110' ;'1'

RETLW B'01011011' ;'2'

RETLW B'01001111' ;'3'

RETLW B'01100110' ;'4'

RETLW B'01101101' ;'5'

RETLW B'01111101' ;'6'

RETLW B'00000111' ;'7'

RETLW B'01111111' ;'8'

RETLW B'01101111' ;'9'

END

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Embeddedsystemsneedtointerfacewiththe

physicalworld

Mustbeabletodetectthestateofthephysical

variablesandcontrolthem

Inputtransducersorsensorsareusedtoconvertphysicalvariablesintoelectricalvariables

Lightsensors

Temperaturesensors

Outputtransducersconvertelectricalvariablesto

physical;actuators

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Sensors


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27

Sensors

The

Microswitch


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Alightdependentresistor(LDR)is

madefrom

apiece

of

exposed

semiconductormaterial

Whenlightfallsonit,itcreates

holeelectronpairsinthematerial,whichimprovesthe

conductivity.

28

Sensors

Light

dependent

Resistors

Illumination(lux) RLDR (Ohms) Vo

Dark 2M 5

10 9000 2.36

1000 400 0.19


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Usefulinsensingthepresenceorclosenessofobjects

Thepresenceofobjectcanbedetected

Ifitbreaksthelightbeam

Ifitreflectsthelightbeam

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Sensors

Optical

Object

Sensing


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Usefulinmeasuringdistanceandspeed

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Sensors

Opto

sensor

as

a

Shaft

Encoder


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Basedonreflectiveprincipleofultrasonicwaves

Anultrasonictransmittersendsoutaburstof

ultrasonicpulsesandthenthereceiverdetectstheecho

Ifthetimetoechoismeasured,distancecanbe

measured

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Sensors

Ultrasonic

Object

Sensor


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Embeddedsystemsneedtocausephysicalmovement

Linearorrotarymotion

Mostactuatorsareelectricalinnature

Solenoids(linearmotion)

Servomotors(rotarymotion)

DCorsteppermotors(rotarymotion)

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Actuators:motorsandservos


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DCMotors

Rangefrom

the

extremely

powerful

to

the

very

small

Widespeedrange

Controllablespeed

Goodefficiency Canprovideaccurateangularpositioningwithangular

shafts

Onlythearmaturewindingneedstobedriven
http://en.wikipedia.org/wiki/File:Electric_motor_cycle_1.png


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StepperMotors

Asteppermotor (orstep

motor)isasynchronouselectric

motorthatcandivideafullrotationintoalargenumberof

steps.


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StepperMotors

Features

Simpleinterfacewithdigitalsystems

Cancontrolspeedandposition Awkwardstartupcharacteristics

Losetorqueathighspeed

Limitedtopspeed

Lessefficient

Morecomplextodrive


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ServoMotors

Allowspreciseangular

motion

Theoutputisashaftthat

cantakeanangular

positionoverarangeof

180o

Theinputtotheservois

apulsestreamwhose

widthdeterminesthe

angularpositionofthe

shaft


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InterfacingtoActuators

Microcontrollerscandriveloadswithsmall

electricalrequirements

Somedevices,likeactuators,requirehighcurrents

or

supply

voltages

Useswitchingdevices

SimpleDCswitchingusingBJTsorMOSFETs

ReversibleDCswitchingusingHbridge


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SimpleDC

interfacing


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SimpleDC

interfacing

Resistiveload Inductiveload


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SimpleDC

interfacing

Characteristicsoftwopopularlogiccompatible

MOSFETs


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Interfacing to ActuatorsDrivingPiezo SounderandOptosensors

Piezo sounderratings:9mA,320V

Theoptosensorfoundtooperatewellwith91Ohmresistor.Thediode

forwardvoltageis1.7V.Therequiredcurrentisabout17.6mA


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Interfacing to ActuatorsReversibleDCSwitching

DCswitchingallowsdrivingloadswithcurrentflowinginone

direction

Someloadsrequirestheappliedvoltagetobereversible;DC

motorsrotationdependsondirectionofcurrent

UseHbridge!


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Interfacing to ActuatorsReversibleDCSwitching

L293D

Dual

H

bridgePeakoutputcurrent1.2Aperchannel


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More on Digital Input

Whenacquiringdigitalinputsintothemicrocontroller,itisessentialthattheinputvoltageiswithinthe

permissibleandrecognizablerangeoftheMC

Voltagerangedependsonthelogicfamily;TTL,CMOS,

Interfacingwithinthesamefamilyissafe

Whatforthecase Interfacingtodigitalsensors

Signalcorruption

Interference


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PIC16F873APortCharacteristics


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FormsofSignalCorruption

Spikesinthesignal

Slowedge DCOffsetinthesignal


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ClampingVoltageSpikes

Allportsareusuallyprotectedbyapairof

diodes

Anoptionalcurrent

limitingresistorcanbe

addedifhighspikesare

expected

IfRprot =1K andthemaximumdiodecurrentis20mAwhenVd=0.3v,thenwhatisthemaximumpositivevoltagespikethatcanbesuppressed?


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AnalogInput

Filtering

CanuseSchmitttriggerforspeedingupslowlogicedges.

SchmitttriggerwithRCfiltercanbeusedtofiltervoltage

spikes.


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SwitchDebouncing

Mechanicalswitchesexhibitbouncingbehavior

Theswitchcontactbouncesbetweenopenandclosed

Aseriousproblemfordigitaldevices?!

Switchdebouncing!!

hardware

and/or

software

techniques


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SwitchDebouncing


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SwitchDebouncing


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09 chapter 8 - human physical interface

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