Introduction to Embedded System I : Chapter 2 (3rd portion)

Introduction to
EMBEDDED SYSTEM
(2nd Edition)
SHIBU K V
Dr Moe Moe Myint
Department of Computer Engineering & Information Technology
Mandalay Technological University
www.slideshare.net/MoeMoeMyint
moemoemyint@moemyanmar.ml
moe2myint.mdy@gmail.com
drmoemoemyint.blogspot.com

Agenda
2.1 Core of the Embedded System
2.2 Memory
2.3 Sensors and Actuators
2.4 Communication Interface
2.5 Embedded Firmware
2.6 Other System Components
2.7 PCB and Passive Components
2
Department of Computer Engineering and Information Technology

Learning Objectives
 Learn the building blocks of a typical Embedded System
 Learn about General Purpose Processors (GPPs), Application
Specific Instruction Set Processors (ASIPs), Microprocessors,
Microcontrollers, Digital Signal Processors, RISC & CISC
processors, Harvad and Von-Neumann Processor Architecture, Big-
endian v/s Little endian processors, Load Store operation and
Instruction pipelining
 Learn about different PLDs like Complex Programmable Logic
Devices (CPLDs), Field Programmable Gate Arrays (FPGAs), etc.
3

Cont’d
 Learn about the different memory technologies and memory types used in
embedded system development
 Learn about Masked ROM (MROM), PROM, OTP, EPROM, EEPROM, and
FLASH memory for embedded firmware storage
 Learn about Serial Access Memory (SAM), Static Random Access Memory
(SRAM), Dynamic Random Access Memory (DRAM) and Nonvolatile
SRAM (NVRAM)
 Understand the different factors to be considered in the selection of memory
for embedded systems
 Understand the role of sensors, actuators and their interfacing with the I/O
subsystems of an embedded system
4

Cont’d
 Learn about the interfacing of LEDs, 7-segment LED Displays, Piezo Buzzer,
Stepper Motor, Relays, Optocouplers, Matrix keyboard, Push button switches,
Programmable Peripheral Interface Device (e.g. 8255 PPI), etc. with the I/O
subsystem of the embedded system
 Learn about the different communication interfaces of an embedded system
 Understand the various chip level communication interfaces like I2C, SPI,
UART, 1-wire, parallel bus, etc
 Understand the different wired and wireless external communication interfaces
like RS-232C, RS-485, Parallel Port, USB, IEEE1394, Infrared (IrDA),
Bluetooth, Wifi, ZigBee, GPRS, etc.
 Know what embedded firmware is and its role in embedded systems
5

Cont’d
 Understand the different system components like Reset Circuit,
Brown-out protection circuit, Oscillator Unit, Real-Time Clock
(RTC) and Watchdog Timer unit
 Understand the role of PCB in embedded systems
6

2.3 Sensors and Actuators
 A sensor is a transducer device that converts energy from one form to another
for any measurement or control purpose.
 The changes in system environment or variables are detected by the sensors
connected to the input port of the embedded system.
 Actuator is a form of transducer device (mechanical or electrical) which
converts signals to corresponding physical action (motion). Actuator acts as an
output device.
 If the embedded system is designed for any controlling purpose, the system will
produce some changes in the controlling variable to bring the controlled variable to
the desired value.
 It is achieved through an actuator connected to the output port of the embedded
system.
7

Cont’d
 If the embedded system is designed for monitoring purpose only, then
there is no need for including an actuator in the system.
 For example, take the case of an ECG machine. It is designed to monitor
the heart beat status of a patient and it cannot impose a control over the
patient’s heart beat and its order. The sensors used here are the different
electrode sets connected to the body of the patient. The variations are
captured and presented to the user (may be a doctor) through a visual
display or some printed chart.
8

I/O Subsystem
 The I/O subsystem of the embedded system facilitates the interaction of the
embedded system with the external world.
 The interaction happens through the sensors and actuators connected to the input
and output ports respectively of the embedded system.
 The sensors may not be directly interfaced to the input ports, instead they may be
interfaced through signal conditioning and translating systems like ADC,
optocouplers, etc.
9

Cont’d
 Light Emitting Diode (LED)
 7-Segment LED Display
 Optocoupler
 Stepper Motor
 Relay
 Piezo Buzzer
 Push Button Switch
 Keyboard
 Programmable Peripheral Interface (PPI)
10

Light Emitting Diode (LED)
 LED is an important output device for visual indication in any embedded
system. LED can be used as an indicator for the status of various signals or
situations. Typical examples are indicating the presence of power
conditions like ‘Device ON’, ‘Battery low’ or ‘Charging of battery’ for a
battery operated handheld embedded devices.
 LED is a p-n junction diode and it contains an anode and a cathode. For
proper functioning of the LED, the anode of it should be connected to +ve
terminal of the supply voltage and cathode to the –ve terminal of the
supply voltage. The current flowing through the LED must be limited to a
value below the maximum current that it can conduct. A resistor is used in
series between the power supply and the LED to limit the current through
the LED.
11

Cont’d12
Figure. LED Interfacing
𝑅 =
(𝑉 − 𝑉𝐿𝐸𝐷)
𝐼

7- Segment LED Display
 The 7-segment LED display is an output device for displaying
alphanumeric characters. It contains 8 light-emitting diode (LED)
segments arranged in a special form. Out of the 8 LED segments, 7 are
used for displaying alphanumeric characters and 1 is used for representing
‘decimal point’ in decimal number display.
 The LED segments are named A to G and the decimal point LED segment
is named as DP.
13

Cont’d14
Figure Common anode and cathode configurations
of a 7-segment LED Display
 The 7-segment LED displays are available in two different configurations,
namely; Common Anode and Common Cathode. In the common anode
configuration, the anodes of the 8 segments are connected commonly
whereas in the common cathode configuration, the 8 LED segments share a
common cathode line.

Cont’d
15
 7-segment LED display is a popular choice for low cost embedded
applications like, Public telephone call monitoring devices, point of sale
terminals, etc.

Optocoupler
 Optocoupler is a solid state device to isolate two parts of a circuit.
 Optocoupler combines an LED and a photo-transistor in a single housing
(package). Figure illustrates the functioning of an optocoupler device.
 Figure illustrates the functioning of an optocoupler device.
16
Figure. An optocoupler device

Cont’d
17
Figure. Optocoupler in Input and Output Circuit
 In electronic circuits, an optocoupler is used for suppressing
interference in data communication, circuit isolation, high voltage
separation, simultaneous separation and signal intensification, etc.
 Optocouplers can be used in either input circuits or in output circuits.
 Figure illustrates the usage of optocoupler in input circuit and output
circuit of an embedded system with a microcontroller as the system
core.

Stepper Motor
 A stepper motor is an electro-mechanical device which generates discrete
displacement (motion) in response to dc electrical signals.
 It differs from the normal dc motor in its operation.
 The dc motor produces continuous rotation on applying dc voltage
whereas a stepper motor produces discrete rotation in response to the dc
voltage applied to it.
 Stepper motors are widely used in industrial embedded applications,
consumer electronic products and robotics control systems.
 The paper feed mechanism of a printer/fax makes use of stepper motors for
its functioning.
18

Cont’d
 Based on the coil winding arrangements, a two-phase stepper motor is
classified into two. They are:
 Unipolar
 Bipolar
19
Stepper Motor

Unipolar
 A unipolar stepper motor contains two windings
per phase.
 The direction of rotation (clockwise or
anticlockwise) of a stepper motor is controlled by
changing the direction of current flow.
 Current in one direction flows through one coil and
in the opposite direction flows through the other
coil.
 It is easy to shift the direction of rotation by just
switching the terminals to which the coils are
connected.
 Figure illustrates the working of a two-phase
unipolar stepper motor.
20
A
C
B D
M
GND
GND
2-Phase unipolar stepper motor

Bipolar
 A bipolar stepper motor contains single winding
per phase.
 For reversing the motor rotation the current flow
through the windings is reversed dynamically.
 It requires complex circuitry for current flow
reversal.
 There is one disadvantage of unipolar motors. The
torque generated by them is quite less. This is
because the current is flowing only through the
half the winding. Hence they are used in low
torque applications.
 On the other hand, bipolar stepper motors are a
little complex to wire as we have to use a current
reversing H bridge driver IC like an L293D. But
the advantage is that the current will flow
through the full coil. The resulting torque
generated by the motor is larger as compared to a
uni-polar motor.
21

Cont’d
 The stepping of stepper motor can be implemented in different ways by
changing the sequence of activation of the stator windings. The different
stepping modes supported by stepper motor are explained below.
 Full Step: In the step mode both the phases are energized
simultaneously. The coils A, B, C and D are energized in the following
order:
22
 It should be noted that out of the two windings, only one winding of a
phase is energized at a time.
Step Coil A Coil B Coil C Coil D
1 H H L L
2 L H H L
3 L L H H
4 H L L H

Cont’d
 Wave Step: In the wave step mode only one phase is energized at
a time and each coils of the phase is energies alternatively. The
coils A, B, C and D are energized in the following order:
23
1 H L L L
2 L H L L
3 L L H L
4 L L L H

Cont’d
 Half Step : It uses the combination of wave and full step. It has
the highest torque and stability. The coil energizing sequence for
half step is given below.
24
1 H L L L
2 H H L L
3 L H L L
4 L H H L
5 L L H L
6 L L H H
7 L L L H
8 H L L H

Cont’d
 The rotation of the stepper motor can be reversed by reversing the
order in which the coil is energized.
 Two-phase unipolar stepper motors are the popular choice for
embedded applications.
 The current requirement for stepper motor is little high and hence the
port pins of a microcontroller/processor may not be able to drive
them directly.
 Also the supply voltage required to operate stepper motor varies
normally in the range 5V to 24 V.
 Depending on the current and voltage requirements, special driving
circuits are required to interface the stepper motor with
microcontroller/processors.
 The following circuit diagram illustrates the interfacing of a stepper
motor through a driver circuit connected to the port pins of a
microcontroller/processor.
25

Cont’d26
Interfacing of stepper motor through driver circuit

Relay
 Relay is an electro-mechanical device. In embedded application, the ‘Relay’ unit
acts as dynamic path selectors for signals and power.
 The ‘Relay’ unit contains a relay coil made up of insulated wire on a metal core and a
metal armature with one or more contacts.
 ‘Relay’ works on electromagnetic principle. When a voltage is applied to the relay
coil, current flows through the coil, which in turn generates a magnetic field.
 The magnetic field attracts the armature core and moves the contact point. The
movement of the contact point changes the power/signal flow path.
 ‘Relays’ are available in different configurations. Figure given below illustrates the
widely used relay configurations for embedded applications.
27

Cont’d
28
Figure Relay Configurations
 The Single Pole Single Throw configuration has only one path for information flow.
The path is either open or closed in normal condition. For normally Open Single
Pole Single Throw relay, the circuit is normally open and it becomes closed when the
relay is energized. For normally closed Single Pole Single Throw configuration, the
circuit is normally closed and it becomes open when the relay is energized. For
Single Pole Double Throw Relay, there are two paths for information flow and they
are selected by energizing or de-energizing the relay.

Understanding Test Questions IV
29
1. Which of the following is (are) example(s) for the input subsystem of an
embedded system dealing with digital data?
(a) ADC (b) Optocoupler (c) DAC (d) All of them
(e) only (a) and (b)
2. Which of the following is (are) example(s) for the output subsystem of
an embedded system dealing with digital data?
(a) LED (b) Optocoupler (c) Stepper Motor(d) All of them
(e) only (a) and (c)
3. Which of the following is true about optocouplers
(a) Optocoupler acts as an input device only
(b) Optocoupler acts as an output device only
(c) Optocoupler can be used in both input and output circuitry
(d) None of these

Cont’d
30
4. Which of the following is true about a unipolar stepper motor
(a) Contains only a single winding per stator phase
(b) Contains four windings per stator phase
(c) Contains two windings per stator phase
(d) None of these
5. Which of the following is (are) true about normally open single pole
relays?
(a) The circuit remains open when the relay is not energized
(b) The circuit remains closed when the relay is energized
(c) There are two output paths
(d) Both (a) and (b) (e) None of these

Reviewed Questions IV31
1. What is Sensor? Explain its role in Embedded System Design?
Illustrate with an example.
2. What is Actuator? Explain its role in Embedded System Design?
Illustrate with an example.
3. Calculate the resistance in the following circuit.
4. What is stepper motor? How is it different from ordinary dc motor?
5. Explain the role of Stepper motor in embedded applications with
examples.
6. What is Relay? What are the different types of relays available?

 Only Original Owner has full rights reserved for copied images.
 This PPT is only for fair academic use.
 Coming soon for chapter 2 (4th portion)
32

Introduction to Embedded System I : Chapter 2 (3rd portion)

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