Switches Displays Solenoids Motors - h Ac

1Dr. Martin LandPeripheral InterfacingEmbedded Systems — Hadassah College — Spring 2011

Hello PhysicalWorldSwitches

Displays

Solenoids

Motors


Inputs + Switches

Power supplySupply voltage (VDD) = logic 1Ground = logic 0

Switch Open — disconnectClosed — connect

Switch with pull-up resistorOpen switch

Input pin = +voltage = logic 1Resistor does nothing

Closed switchInput pin = ground = logic 0Resistor prevents short circuit of VDD to ground

PIC configurable with internal pull-up resistors

InputPin

VDD

0 RSwitch

1

Physical abstraction model

InputPin

0

InputPin

VDD

1


Light Emitting Diode (LED)

Output pin → resistor → LED → groundOutput pin = logic 1

Current through LED LED emits light

Output pin = logic 0 No current through LEDLED off

VDD → resistor → LED → output pinOutput pin = logic 0

Current through LED to output pinLED emits light

Output pin = logic 1 No current through LEDLED off

OutputPin

VDD

Physical abstraction model

OutputPin

Controller with Switch and LEDInput

Port B pin RB<k>TRISB<k> = 1

Connected to VDD = logical 1 through switch KSwitch K open ⇒ RB<k> = 1 Switch K closed ⇒ RB<k> = 0

OutputsPort B pins RB and RB<j>

TRISB = TRISB<j> = 0

LED1 emits when RB = 0LED2 emits when RB<j> = 1


Switch BounceReal physical switch

Cannot open / close instantaneouslyVoltage "bounces" or "rings" on transitionsIdeal input

Measured input

Input from a bouncy switch

Switch Input CodeTEMP equ 0x20 ; Temp data storagek equ 3 ; switch connected to RB<3> READ_K:

btfss PORTB, k ; Skip next if (RB<k> == 1)goto K0movlw 1 ; W ← 1movwf TEMP ; TEMP ← 1goto K1

K0: clrf TEMP ; TEMP ← 0K1: call wait20 ; RB<k> measured → wait 20 ms

btfss PORTB, k ; Skip next if (RB<k> == 1)goto K2movlw 1 ; W ← 1goto K3

K2: clrw ; W ← 0K3: xorwf TEMP, W ; W ← !(TEMP == W) with Z set

btfss STATUS,Z ; Skip next if (TEMP == W)goto READ_K ; Start over

K4: movf TEMP, W ; W ← TEMP


KeypadSwitch matrix

Key press closes switch at row + columnExploration lines

MCU output pins Return lines

MCU input pins = 0 No key press ⇒ return lines = 1

Sequential explorationKey (i,j) pressedExploration lines ← 0 sequentially j = 0, 1, 2, 3Return line i ← 0 when exploration line j ← 0

Parallel explorationKey (i,j) pressedAll exploration lines ← 0 ⇒ exploration line j ← 0 Swap exploration / return lines ⇒ new return line i ← 0


Press Key 6Sequential read

11113

11112

10 111

11110

3210

Rtrn

Expl

3

2

1

0

3210


Read 1Exploration lines on rows

All rows ← 0

Return lines on columnsColumn 2 ← 0

Read 2Exploration lines on columns

All columns ← 0

Return lines on rowsRow 1 ← 0

Press Key 6Parallel read

3

2

1

0

3210

Switch Matrix on PIC Port BExploration lines

RB<3:0>

Return linesRB<7:4>

Internal pull-up resistorsConfigurable on Port BRB<7:4>

Default to 1External switch can

pull down to 0

VDD

0 RSwitch

1

InputPin

PICMCU

Subroutine for Keyboard Read — 1

list p = 16f873

#include <p16f873.inc>

; Declaration temporary register names

TEMP equ 0x20

ROW equ 0x21

COLUMN equ 0x22

INITKEY: ; Configure port B

clrf STATUS ; Bank 0

bcf INTCON,INTE ; Disable external interrupt by RB0

bcf INTCON, RBIE ; Disable interrupt by changes in RB<7:4>

movlw 0FFh ; Store value in PORTB

movwf PORTB ; Set all outputs in port B to 1

bsf STATUS, RP0 ; Bank 1

movlw F0h ; TRISB W ← 1111 0000 movwf TRISB ; RB<3:0> — outputs and RB<7:4> — inputs

bcf OPTION_REG, 7 ; Enable internal pull-ups in port B

bcf STATUS, RP0 ; Bank 0

return

; Configure port B

READKEY: movlw F0h movwf PORTB ; Set all rows to 0 ⇒ write RB<3:0> nop KEY10: ; Wait for no key presses (KB free) movf PORTB, W ; Read all columns ⇒ read RB<7:4> ; Key press ⇒ WH = 1 except key line xorlw F0h ; All bits of WH = 0 except key line ; Z ← 1 if no key pressed btfss STATUS, Z ; Skip next if (Z == 1) key press goto KEY10

Wait for inactive keypadIgnore previous key presses

RB<3:0> — outputsRB<7:4> — inputs



KEY20: movlw F0h ; Repeat reading of input lines movwf PORTB ; testing of lines nop ; waiting for key press movf PORTB, W xorlw F0h btfsc STATUS, Z ; Skip next if !(Z == 1) ⇒ key press goto KEY20 KEY30: ; Continue on key press call DELAY20 ; 20 ms delay for debouncing KEY40: ; Explore keypad row by row movlw FFh ; All rows to 1 movwf PORTB nop ROW0: ; Explore row 0 movlw 0 ; W ← 0 movwf ROW ; ROW ← W bcf PORTB, 0 ; Row 0 ← 0 (RB0) nop movf PORTB, W ; Read all columns simultaneously call IDENTIFY ; Subroutine to identify column btfsc STATUS, C ; Skip next if (C == 1) goto KEY50 ; Finish exploration bsf PORTB, 0 ; Row 0 ← 1 (RB0) nop

Explore Row 0

Wait for key press



Explore Rows 1 – 3ROW1: ; Explore row 1 movlw 1 ; W ← 1 movwf ROW ; ROW ← W bcf PORTB, 0 ; Row 1 ← 0 (RB0) nop movf PORTB, W ; Read all columns simultaneously call IDENTIFY ; Subroutine to identify column btfsc STATUS, C ; Skip next if (C == 1) goto KEY50 ; Finish exploration bsf PORTB, 0 ; Row 1 ← 1 (RB0) nop ROW2: ; Explore row 2 movlw 2 ; W ← 2 movwf ROW ; ROW ← W bcf PORTB, 0 ; Row 2 ← 0 (RB0) nop movf PORTB, W ; Read all columns simultaneously call IDENTIFY ; Subroutine to identify column btfsc STATUS, C ; Skip next if (C == 1) goto KEY50 ; Finish exploration bsf PORTB, 0 ; Row 2 ← 1 (RB0) nop ROW3: ; Explore row 3 movlw 3 ; W ← 3 movwf ROW ; ROW ← W bcf PORTB, 0 ; Row 3 ← 0 (RB0) nop movf PORTB, W ; Read all columns simultaneously call IDENTIFY ; Subroutine to identify column btfsc STATUS, C ; Skip next if (C == 1) goto KEY50 ; Finish exploration bsf PORTB, 0 ; Row 3 ← 1 (RB0) nop

Routines Row 0 – Row 3Return row number in

temp register ROWCalls IDENTIFY to

locate COLUMN

Temp registers (ROW, COLUMN) ← row, column

00000000 ≤ ROW ≤ 00000011

00000000 ≤ COLUMN ≤ 00000011

goto KEY20 ; False key pressed — start over

KEY50: ; Build 4-bit exploration code from ROW: COLUMN

rlf ROW, f ; ROW<2:1> ← row number rlf ROW, W ; W<3:2> ← row number andlw FCh ; W<1:0> ← 0 iorwf COLUMN, W ; W<1:0> ← COLUMN andlw 0Fh ; W<7:4> ← 0 return ; Return exploration code in W<3:0>

; End of main program



Subroutine IDENTIFYReturns COLUMN

IDENTIFY: movwf TEMP ; TEMP ← W btfsc TEMP, 4 ; Skip next if (column0 == 0) goto COL1 ; Next column movlw 0 ; W ← 0 movwf COLUMN ; COLUMN ← W goto IDENT_FIN ; Finish subroutine COL1: btfsc TEMP, 5 ; Skip next if (column1 == 0) goto COL2 ; Next column movlw 1 ; W ← 1 movwf COLUMN ; COLUMN ← W goto IDENT_FIN ; Finish subroutine COL2: btfsc TEMP, 6 ; Skip next if (column2 == 0) goto COL3 ; Next column movlw 2 ; W ← 2 movwf COLUMN ; COLUMN ← W goto IDENT_FIN ; Finish subroutine COL3: btfsc TEMP, 7 ; Skip next if (column3 == 0) goto COL4 ; Next column movlw 3 ; W ← 3 movwf COLUMN ; COLUMN ← W goto IDENT_FIN ; Finish subroutine COL4: bcf STATUS, C ; Return "key not pressed" as C = 0 return ; Return IDENT_FIN: bsf STATUS, C ; Return "key pressed" as C = 1 return ; Return DELAY20 ; 20 ms delay subroutine return end


Alphanumeric DisplayLED (light emitting diode)

7 segment display Segments a – g separately controlled0 to 9, A, B, C, d, E, F, decimal point

Configurations Common anode

All anodes (+ side) connected to VDD

Active segment ← logic 0 from MCU output pinCommon cathode

All cathodes (– side) connected to ground Active segment ← logic 1 from MCU output pin

LCD (liquid crystal display)Pixel-based display of various resolutionsDedicated driver chip

Converts character to pixel pattern

Seven‐Segment LED4 digit display

Port B RB<7:0> controls 7 segments + decimal RB = 0 activates segmentRB<0> → a , ... , RB<6> → g , RB<7> → dp

Port A RA<3:0> selects digit to activateTransistor arrangement → RA = 0 selects common anode iEach digit activated at f > 40 Hz (faster than human eye)

RA3

RA2

RA1

RA0

< 25 ms

RB7

RB6

RB5

RB4

RB3

RB2

RB1

RB0

RA3

RA2

RA1

RA0

Outline of LED Display RoutineData

Data register ← data byteKeypad, measurement, calculation

Conversions3 decimal character registers ← data byte (hexadecimal value)

Calculation or ROM look-up

For each character, 7-bit string to activate segmentsROM look-up

OutputsPort A RA<2:0> provides character activation patterns

Divide 24 ms refresh interval into 3 sub-intervals of 8 msCycle through 3 data words — 11111110, 11111101, 11111011

Port B RB<6:0> provides segment activation patterns from ROM


MagnetsPermanent ferromagnet

Metal (typically iron) with permanent magnetic fieldCompass aligns with earth's magnetic field

Mechanical forcesOpposite poles (N ↔ S) attract

Like poles (N ↔ N / S ↔ S) repel

ElectromagnetElectric current in wire coil (winding) → magnetic field

Field configuration — like permanent bar magnet

Current level + direction → field strength + polarity

N

S

http://hyperphysics.phy‐astr.gsu.edu/hbase/magnetic/elemag.html

NSSN

SNNS

SNSN

NSNS


SolenoidSolenoid actuator

Iron core moves in wire coilNo current

Spring pushes core out of coil

Current → magnetic fieldField pulls core into coil

Current → lateral motion

ApplicationValves

Irrigation, washing machine, industrial

LocksLinear motion

Video tape, DVD drive

Switches / relayshttp://boomeria.org/physicslectures/secondsemester/electricity/electromagnetism/electromag.htmlhttp://parts.digikey.com

Magnetic Force

spring

Electric Current


DC Electric MotorsRotor (armature)

Rotating central axis Stator

Static frame Mechanical force

Fixed magnet Permanent magnet or coil with constant current

Variable electromagnetCoil with varying currentAlways rotates rotor away from like pole / toward opposite pole

Basic typesBrushed DC motor — variable magnet on rotorBrushless DC motor (stepping motor) — variable magnet on stator

OperationSpeed = constant × voltageReverse voltage ⇒ reverse direction http://www.midwestsalon.com

rotor

stator

N SN

SStator

Rotor


Brushed DC MotorStator

Fixed magnetic fieldRotor

Rotating coil magnetCoil winding

Front to backRight to left

BrushesConnect coils to current

CommutationGap between brushes

Swaps current direction when rotor rotates

Current always Enters on right side of coilLeaves on left side of coil

Field always opposes stator

N S

current stator

rotor

brushes

http://www.cvel.clemson.edu/auto/actuators/motors‐dc‐brushed.html


Brushed DC Motor Rotation Phases


Types of Brushed DC Motors

Stator field Permanent magnets

Advantages Most common Least complexLeast expensiveSpeed linear in voltage

DisadvantageMagnets weaken over time

Permanent magnet brushed DC (PMDC) motors



Stator field Coil in parallel (shunt) with armature

Advantage Speed linear in voltage

DisadvantageNot suited to varying loadHigher load → higher current → overheating

Shunt‐wound brushed DC (SHWDC) motors



Stator field Coil in series with armature

Advantage Suited to varying loadHigher load → speed drops → higher current → higher torque

DisadvantageSpeed depends on load

Series‐wound brushed DC (SWDC) motors


Control Circuits for DC MotorsPower

Supplied separately to MCU + motorMotor ← higher voltage / current than MCU

ControlMCU output signals

Sets motor speed + direction

Amplified by control circuit Power to motor determined by control signals

FeedbackMeasure motor speed → MCU MCU adjusts control signal

Responds to goal + measured result

Power

PowerSpeed

indication

Control

Feedback

MCU

PowerSupply

ControlCircuit

Motor

Control Circuit Output→MCU Output


Elementary Control Theory

Physical stateVariables (functions of time) required to describe systemExamples — motor speed, direction, current, torqueNot all state variable are measured

Target stateDesired values of state variables

Physical modelMathematical description of system dynamics How system responds to external stimulusExample — relationship of voltage + motion for motor under load

ControlIndependently inputs to physical systemExternal stimulus applied by user

ControllabilityCan bring system to any desired state with appropriate control

Definitions

PhysicalState

PhysicalModel

measuredstatecontrol

Physical System


FeedbackDevices

Amplifier A — amplifies Input → OutputSampler B — samples Output → SampleFeedback ⊕ — combines Sample + Control → Input

Feedback Sample of output state "fed back" to controllerControl loop

Control → sample → feedback (compare sample + target)

Control Input Output

Sample

http://en.wikipedia.org/wiki/Feedback


Open Loop ControlOpen loop = no loop

ExampleSimple (ideal) permanent magnet motor

Model Voltage = k × Speed

Target state Speed = S0Control Voltage = k × S0

PhysicalState

PhysicalModel


Physical System

Calculator

MathematicalModel

targetstate

Controller

( ) ( ) ( )( )( ) ( )( )n+1 n n

n+1 n

state t = F state t , control t

control t = G target state t


Closed Loop ControlClosed loop = sampling feedback loop

ExampleSimple permanent magnet motor

Model Voltage = k × Speed

Target state Speed = S0Control Voltage = function (k × S0 , measured speed)

PhysicalState

PhysicalModel


Physical System

Calculator

MathematicalModel

Sampler

targetstate

Controller

feedback

( ) ( ) ( )( )( ) ( ) ( )( )n+1 n n

n+1 n n

state t = F state t , control t

control t = meG tar asurget stat ed stae , te tt


ControllabilityState controllable

Some control signal can bring system to arbitrary stateOutput controllable

Some control signal can bring output to arbitrary stateSome unmeasured state variables not controllableExample

Permanent magnet motorSpeed measured and controllableElectromagnetic noise not measured or controlled

Examples of non-fully-controllable systemShunt-wound motor

Speed controllable under reasonable loadCannot control speed, current, and temperature under varying load

Series-wound motorOperates under varied loadCannot achieve target speed under any load


Abstraction Model for Brushed DC Motor

Motor parametersMechanical friction BElectrical resistance R

External sourceInput voltage VIN

Motor speedS rotations per minute

Back electromotive force (BEMF)Voltage generated by motor rotationDepends on speed of motorBEMF = V1 – V2 = k × S

MotorV1

V2

RVIN

IM

Parameters


Abstraction Model for Brushed DC Motor

Steady state motion

General case

Ideal caseFriction B → 0 ⇒

( )IN M 1 2

d d d dV S I V V 0

dt dt dt dt= = = − =

Equations of motion

MotorV1

V2

RVIN

IM

( )

IN2

M IN2

1 2 IN2

kMotor speed S V

k RBB

Electric current I Vk RB

1BEMF V V k S V

1 RB/k

=−

=−

− = × =−

IN

M

1 2 IN

1Motor speed S V

kElectric current I 0

BEMF V V V

→

→− →


Open Loop Brushed DC Motor Control

Ideal linear controlSpeed = VIN / k

Pulse Width Modulation (PWM)Control signal with PERIOD T and DUTY CYCLE D

Voltage averagingRotor coil ⇒ low pass filter

Unidirectional control

TDVmax

0

( )IN

max max

max

1 DD V T D 0 V

T TD

Speed Vk T

⎡ ⎤= × + − × = ×⎣ ⎦

= ××

Motor voltage = time average of control voltage V

control voltage VIN Motor


Open Loop Brushed DC Motor Control

Ideal direction controlSpeed = (V1 – V2) / k

H-Bridge circuitMCU controls 4 independent output voltagesIdeal control abstraction

Controli = switchi for i = 1, 2, 3, 4

Bidirectional control

MotorV1

V2

Motor

Vsupply

Control1

Control2

Control3

Control4

V1

V2


Open Loop Brushed DC Motor ControlControl signals to H‐bridge

Motor

Vsupply

Control1

Control2

Control3

Control4

V1

V2

ONOFFONOFFBrake

OFFOFFOFFOFFCoast

OFFONONOFFReverse

ONOFFOFFONForward

CTRL4CTRL3CTRL2CTRL1

Motor

Vsupply

Control1

Control2

Control3

Control4

V1

V2

Motor

Vsupply

Control1

Control2

Control3

Control4

V1

V2

Motor

Vsupply

Control1

Control2

Control3

Control4

V1

V2

Forward

Reverse

Coast

Brake


Closed Loop Brushed DC Motor Control

Optical encoderSlotted wheel attached to motorLED → slotted wheel → photo transistorFrequency of light pulses → motor speed

Hall effect sensorMagnets on wheel attached to motorSensor generates pulse when magnet passes

Feedback sensors

Hall effect

Metal conductor in magnetic field

Current flows through conductor

Metal generates voltage

Voltage ⊥ current ⊥ fieldhttp://en.wikipedia.org/wiki/Hall_effect


Closed Loop Brushed DC Motor Control

Realistic model of motorElectrical resistance motor and switches Friction in motor V1 – V2 ≠ Vsupply

Speedmeasured = [(V1 – V2)measured] / k

BEMF speed controlMeasure + amplify V1 – V2

Read measurement with MCU A/D

Back electromotive force (BEMF) sensing

Motor

Vsupply

Control1

Control2

Control3

Control4

MCU

Control1, Control

2,

Control3, Control

4

A/D a(V1 ‐ V

2)

V1

V2


STMicroelectronics L293D Dual H‐BridgeElectrical connections

VS Motor supply voltage VSS Logic supply voltageGND Ground

Truth table

HHH

LHL

ZLH

ZLL

OutputEnableInput

Z = high impedance = equivalent to disconnected

10 V

Example5 V

Ground Ground

motorA

BE

Coastxx0

1

1

1

1

E

Brake11

Reverse10

Forward01

Brake00

MotorBA

Brushless DC MotorsCommon applications

Automated machines, printers, volumetric pumpsAdvantages

Brushless Fewer failures

No electrical arcs — undesirable / dangerous in some environments

Speed independent of load (< torque rating for motor)

Open loop positioning Move in quantized steps

Position of rotor known without feedback mechanism

Holding Torque Can hold rotor stationary

Excellent response Controllable start, stop, reverse


Types of Stepping MotorVariable reluctance motor

Soft iron rotor with teethTeeth attracted to magnetic coils on stator

Permanent magnet motorRotor constructed from magnetic stripsAttracted / repulsed by magnetic coils on statorWiring types

Unipolar winding — 3 contacts per coilBipolar winding — 2 contacts per coilBifilar winding — twin coils in parallel

Hybrid stepping motorCombines aspects of permanent magnet and variable reluctance

www.solarbotics.net/library/pdflib/pdf/motorbas.pdf


Variable Reluctance Motor — 1

Voltage to A / A' Voltage to D / D' Voltage to C / C'

Voltage to B / B' Voltage to A / A' Voltage to D / D'


Variable Reluctance Motor — 215o rotation per step

Tooth 1 from pole A to pole C = 90o = 6 steps24 steps for full rotation

Control sequences for full counterclockwise rotation

0100 0100 0100 0100 0100 0100D / D'

0010 0010 0010 0010 0010 0010C / C'

0001 0001 0001 0001 0001 0001B / B'

1000 1000 1000 1000 1000 1000A / A'


Permanent Magnet Motor

Two windings with center tapCenter taps wired to power supply Ends of coils alternately grounded

Current direction Depends on half winding energized

SteppingsHalf power

1 coil energized per step

Full Power2 coils energized per step

Half-steppingCombined half / fullRotor moves half step

MicrosteppingPWM modulation of coils

Unipolar winding

Pole

Coil

NS——2b

SN——2a

——NS1b

——SN1a

2 2'1'1

1

1'

2 2'


Permanent Magnet MotorUnipolar winding steppings

001110000011100000111000

000000111000001110000011

000011100000111000001110

111000001110000011100000

Half‐SteppingFull PowerHalf Power

011001100110

100110011001

001100110011

110011001100

0100010001002b

0001000100012a

0010001000101b

1000100010001a


Permanent Magnet Motor

Two windings with no center tapPowered by H-bridge control circuitCoil attracts / repels rotor poles

Current direction Depends V1 and V2 in H-bridge

Bipolar winding

2b–

2b–

1b+

1b–

Pole

Coil

NS——2a+

SN——2a+

——NS1a–

——SN1a+

2 2'1'1

1

1'

2 2'

Full PowerHalf Power

+--++--++--+

-++--++--++-

--++--++--++

++--++--++--

0-0+0-0+0-0+2b

0+0-0+0-0+0-2a

-0+0-0+0-0+01b

+0-0+0-0+0-01a


MicrosteppingProblems with single stepping

Jerky motor movement at low speedNoisy

Advantage of microstepping Smoother transition

Increase step resolution Reduce noise

Microstepping techniquePulse width modulate coils voltages

Duty cycle of signal to coil lowered Duty cycle of signal to next winding raised

Sine-cosine microstepping

1 MAXmicrosteps

2 MAXmicrosteps

π θI I sin

2 N

π θI I cos

2 N

⎛ ⎞= ⎜ ⎟⎜ ⎟

⎝ ⎠⎛ ⎞

= ⎜ ⎟⎜ ⎟⎝ ⎠ Nmicrosteps = microsteps per step

I1

I2

θ = angular position of rotor


Microstepping ControllerControl inputs for coil x = 1, 2

MCU binary output port pinsCTRLx1, CTRLx2

MCU PWM output pinsP1x on duty cycle D

Sine / cosine valuesGenerate look-up table using

Coil 1

Vsupply

V1

V2

Coil 2

Vsupply

V1

V2

CTRLA1 P1A⋅

CTRLA2

CTRLA2

CTRLA1

CTRLB1 P1B⋅

CTRLB2

CTRLB2

CTRLB1

10Reverse

01Forward

CTRLx2CTRLx1

Modulation

IMAX × DIMAX

IMAX × DIMAX

P1x = PWMP1x = 1

( )step bit‐resolution

microsteps

ND cos π 2 1

N 1

⎛ ⎞= × −⎜ ⎟⎜ ⎟+⎝ ⎠

Switches Displays Solenoids Motors - h Ac

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Transcript of Switches Displays Solenoids Motors - h Ac