hardware lec2

8/8/2019 Hardware Lec2

1/40

Hardware Design

Amr Mokhtar


2/40

Agenda

Introduction

I/O ports: LED, Switch and Relay

Keypad

7-Seg. Display

LCD Display DC Motor

Stepper Motor

Sensors

RS-232

I2C

Copyright 2009 Embedded

Systems Committee


3/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


4/40

Basic Control System


Systems Committee

Plant

Process

Sensor

Actuator

Controller


5/40

Microcontroller Peripherals

Power - Vcc, GND, AVcc, Aref, AGND

Reset - RESET

Crystal - XTAL1, XTAL2

I/O Port - PA[7;0], PB[7:0], PC[7:0],

External interrupts - INT0, INT1,

Timer sources - T0, T1,

Timer/Counters with Prescalers, Compare Modes and Capture Mode

PWM Channels

ADC

Two-wire Serial Interface (TWI or I2C) - SDA, SCL

Programmable Serial USART - RXD, TXD

Master/Slave SPI Serial Interface - MISO, MOSI, SCK, CS Programmable Watchdog Timer

On-chip Analog Comparator


Systems Committee


6/40

Power Supply Circuit


Systems Committee


7/40

Basic Circuit


Systems Committee

Reset Circuit

Oscillator Circuit


8/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


9/40

I/O PORTS: LED


Systems Committee

Switch Interfacing Power LED InterfacingLow power LED


10/40

I/O PORTS: SWITCH


Systems Committee

Reading digital signal (using Opto-Isolation)


11/40

I/O PORTS: RELAY


Systems Committee

RELAY ON I/O PORT USING ULN

fly-back diode


12/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


13/40

KEYPAD


Systems Committee

A switch cannot change state in less than 200 ms A periodic scan is performed, each row is enabled in turn, and the

four buttons of a row are scanned Debouncing also must be carried out (software in 99% of the cases) The solution clearly saves 50% of I/O pins !

Row outputs

Row enables


14/40

Switch Debouncing

Could be done in software or hardware

It relies on the fact that bouncing takes amaximum period of 20-30 ms

The basic idea is to implement a delay after thefirst detected edge, during which no scanning forthe switch is done

After the delay period is finished, scanning canproceed

This way the bouncing can be avoided


Systems Committee


15/40

Switch Debouncing..

Switch bouncing effect

Charging eq. discharging eq.

&

MC14490 Hex Contact Bounce Eliminator ChipMAX6816-MAX6818 Switch Debouncers


Systems Committee


16/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


17/40

7-segment display

LED displays are

1. Power-hungry (10mA per LED)

2. Pin-hungry (8 pins per 7-seg display)


Systems Committee


18/40

7-segment display..

Segment number pin number

a PA.0

b PA.1

c PA.2

d PA.3

e PA.4

f PA.5

g PA.6

dp PA.7


Systems Committee

Digit Seg. h Seg. g Seg. f Seg. e Seg. d Seg. c Seg. b Seg. a HEX

0 1 1 0 0 0 0 0 0 C0

1 0 0 0 0 0 1 1 0 06

2 1 0 1 0 0 1 0 0 A4

3 1 0 1 1 0 0 0 0 B0

4 1 0 0 1 1 0 0 1 99

Using software


19/40

7-segment display..


Systems Committee

Using 7-segment decoder


20/40

Multiplexed 7-seg display


Systems Committee

A normal human eye recognizes about 25 images persecond

A LED flashing at a faster rate (> 50) is recognized assteady and not flashing

Instead, the eye recognizes the average light emittedas steady light

7-seg current supply and number ofsegments.. Tradeoff & limited !


21/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


22/40

LCD

8 data pins D7:D0Bi-directional data/command pins.

RS: Register SelectRS = 0 -> Command Register is selected

RS = 1 -> Data Register is selected

R/W: Read or Write0 -> Write, 1 -> Read

E: Enable (Latch data)To latch the data present on the data pins.

Vo : contrast control


Systems Committee


23/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


24/40


25/40

2. PWM Control of DC Motor


Systems Committee

PWM means how fast we turn the motor ON and OFF

The motor will take the average current

Lower frequency PWM gives better efficiency

Using as high a frequency as possible is better for the

motor

BUT, too high frequency, the H-bridge efficiency starts to

suffer

Usually, 1 to 4 kilohertz is good even though the motorswill make an irritating whine

Big capacitors across the motor terminals help a littlespecially for higher PWM frequencies


26/40

2. PWM Control of DC Motor..


Systems Committee


27/40

Bidirectional DC Motor Control


Systems Committee

DUAL FULL-BRIDGE DRIVER (L298)


28/40

Shaft Encoders

Absolute encoder

The encoder is 3-bits, meaning that it

divides the circle into 8-sectors

Differential encoder How to determine direction of rotation ?


Systems Committee

A pair of LEDs is used having a 90phase difference between them


29/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


30/40

Stepper Motor

Basic Sequence: 0001

0010

0100

1000

Half-Stepping sequence: 0001

0011

0010

0110

0100

1100

1000

1001

The frequency of the sequence determines the speed

of the motor The order of the sequence determines the direction of

rotation


Systems Committee


31/40

Stepper Motor..


Systems Committee


32/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


33/40

Sensors


Systems Committee

LM335 Vs. LM35as analog temperature sensors


34/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


35/40

UART

The tasks of serial communications needs a dedicated hardware

circuit

The circuit needs good synchronization between Tx and Rx so

standard baud rates exist in order to standardize serialcommunications, as:

100, 200, 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200bps


Systems Committee

MCU Device

TX

RX

RX

TX


36/40

RS-232


Systems Committee

Standard serial interfacing of

microcontroller (TTL) with PCor any RS232C Standarddevice , requires TTL to RS232

Level converter

RS-232 Voltage levels

1. +3 to +25 volts to signify a"Space" (Logic 0)

2. -3 to -25 volts for a "Mark"(logic 1)

3. Any voltage in between theseregions (i.e. between +3 and-3 Volts) is undefined.

MAX232 is used


37/40

Agenda

Introduction


Keypad

7-Seg. Display

LCD Display

DC Motor

Stepper Motor

Sensors

RS-232

I2C


Systems Committee


38/40

Inter Integrated Circuit I2C


Systems Committee


39/40

Thank you for coming, listening &

pat ie nce . !


40/40

info@ e scommit t e e . com

e ducat ion@e scommit t e e . com
mailto:[email protected]:[email protected]:[email protected]:[email protected]

hardware lec2

Documents