This document provides an overview of embedded systems concepts including pulse width modulation (PWM), servo motors, DC motors, timers, analog to digital converters (ADCs), and different types of ADCs. It discusses how PWM is used to control servo and DC motors. It also explains the different timer modes for microcontrollers and how timers can generate PWM signals. Finally, it summarizes various ADC types including parallel, ramp counter, and successive approximation designs.

1. Embedded System
ENG.KEROLES SHENOUDA
1

2. Index (1/4)
 PWM (pulse width Modulation)
 What is PWM
 How Does A Servo Motor Work?
 Lab1/Test Servo Motor By Atmega 32
 DC Motor
 L293D
 Atmega 32 Timer 0 Modes
 Request time equation
 Fast PWM Mode
 Phase Correct PWM Mode
2

3. Index (2/4) 3
 Timer0_Register Description
 Assignments
Repeat Lab1/2 by using Timer0
 ADC “Analog Digital Converter”.
 ADC introduction
 ADC Application: Embedded
systems receive
 Concepts: Embedded
Communication “PCM”ss
 Sampling (Hand writing)
time domain

4. Index (3/4) 4
 Sampling (Hand writing)
Frequency Domain
 Quantizer
 Quantizer Types
 Simply we can consider ADC as
 Resolution
 ADC Types

5. Index (4/4) 5
 ADC Parallel Design
 DAC-Based Designs
 Ramp counter ADC
 Successive Approximation ADC
 Sigma-delta design
 ADC on ATMEGA32
 ADC Features in Atmega32
 Interfacing Sensors
 ADC Registers
 Project: GATEWAY CAR Parking

6. PWM (pulse width
Modulation)
6

7. What is PWM ?
 A PWM Signal is a periodic rectangular pulse.
Frequency = 1/T
Duty Cycle = (T_ON/T)
 Pulse width modulation (PWM) is a powerful technique for controlling analog
circuits with a microprocessor's digital outputs. PWM is employed in a wide variety
of applications, ranging from measurement and communications to power control
and conversion.
7

8. What is need of PWM?
 PWM is mainly used for controlling the speed of DC motors . By pulse width
modulation we can get a variable voltage digitally, that is we get voltages
between 0 and VCC by switching the VCC on and off periodically . Other
applications are fading Led , getting different tones in Buzzer,Contolling the
degree of rotation of Servo motor .
8

9. How Does A Servo Motor Work?
 Usually a servomotor turns 90° in either direction, i.e. maximum movement can be
180°
 Three wires are taken out of a servo: positive, ground and control wire.
 A servo motor is controlled by sending a Pulse Width Modulated (PWM) signal
through the control wire. A pulse is sent every 20 milliseconds.
 Width of the pulses determine the position of the shaft. For example, a pulse of
1ms will move the shaft anticlockwise at -90°, a pulse of 1.5ms will move the shaft
at the neutral position that 0° and a pulse of 2ms will move the shaft clockwise
at +90
9

10. How Does A Servo Motor Work?
 Width of the pulses determine the position of the shaft. For example, a pulse of
1ms will move the shaft anticlockwise at -90°, a pulse of 1.5ms will move the shaft at the neutral position that 0°
and a pulse of 2ms will move the shaft clockwise at +90
10

11. Servo motor
 Servo motor works on PWM (Pulse width
modulation) principle, means its angle of rotation is
controlled by the duration of applied pulse to its
Control PIN. Basically servo motor is made up of DC
motor which is controlled by a variable resistor
(potentiometer) and some gears
11

12. Servo motor (another degree
range)(Motor-PWMSERVO in ISIS)
 Servo motor can be rotated from 0 to
180 degree, but it can go up to 210
degree, depending on the
manufacturing. This degree of rotation
can be controlled by applying
the Electrical Pulse of proper width,
to its Control pin. Servo checks the
pulse in every 20 milliseconds. Pulse
of 1 ms (1 millisecond) width can
rotate servo to 0 degree, 1.5ms can
rotate to 90 degree (neutral position)
and 2 ms pulse can rotate it to 180
degree.
12

13. Lab1/Test Servo Motor By Atmega 32
 With out any timer, run a servo Motor (Motor-PWMSERVO ) in ISIS
 Angle 0,90 and 180 as shown below
13

14. Lab1/Test Servo Motor By Atmega 32
 With out any timer, run a servo Motor (Motor-PWMSERVO ) in ISIS
 Angle 0,90 and 180 as shown below
14

15. Lab1/Test Servo Motor By Atmega 32
 With out any timer, run a servo Motor (Motor-PWMSERVO ) in ISIS
 Angle 0,90 and 180 as shown below
15

16. Lab1/Test Servo
Motor By
Atmega 32
Solution
16

17. DC Motor
 This DC or direct current motor works on the principal, when a current carrying
conductor is placed in a magnetic field, it experiences a torque and has a tendency
to move.
17

18. Lab2/ write embedded C Code without
timer to run two DC Motors
 First DC Motor Connect to PD0 (run Clockwise)
 Second DC Motor Connect to PD1 (run Anticlockwise)
 Sequence (Motor 1 run) > Motor1 stop & Motor 2 run
And so on
 Choose the time you prefer
18

19. Lab2/ sequence 19

20. LAB2/Solution 20

21. We can’t connect a DC Motor directly to a
microcontroller ?
 A microcontroller can’t supply the current required for the working of DC
Motor. ATmega32 Microcontroller can source or sink currents up to 40mA but a DC
Motor needs current very much more than that.
 The negative voltages created due to the back emf of the motor may affect the
proper functioning of the microcontroller.
 You may need to control the direction of rotation of the motor by changing the
polarity of the motor supply.
 The operating voltage of the DC Motor may be much higher than the operating
voltage of the microcontroller.
21

22. L293D
 To solve these problems you may use transistorized H Bridge in which freewheeling
diodes are used to avoid problems due to back emf. Thus it requires minimum four
transistors, diodes and resistors for each motor. It is better to use readymade ICs such
as L293D or L293instead of making your own H Bridge, which simplifies your project.
 L293D is a Quadruple Half H-Bridge driver commonly used for motor driving. We
needn’t connect any transistors, resistors or freewheeling diodes. All the four outputs of
this IC are TTL compatible and output clamp diodes are provided to drive inductive
loads. L293D can provide up to 600mA current, in the voltage raging from 4.5 to 36v.
L293 is a similar IC which can provide up to 1A in the same voltage range.
 L293 or L293D contains four Half H Bridge drivers and are enabled in pairs. Input
EN1 is used to enable pair 1 (IN1-OUT1, IN2-OUT2) and input EN2 is used to enable
pair 2 (IN3-OUT3, IN4-OUT4). We can drive two DC Motors with one L293D, but here
for demonstration we are using only one. You can connect second DC Motor to driver
pair 2 according to your needs.
22

23. Control Signals and Motor Status
PC0/IN1 PC1/IN2 Motor Status
LOW LOW Stops
LOW HIGH Clockwise
HIGH LOW Anti-Clockwise
HIGH HIGH Stops
23

24. If we can generate PWM by GPIO and Delay,
Why we need to use TIMER Module to generate PWM ?
24

25. Atmega 32 Timer 0 Modes
Normal Mode
Clear Timer on Compare Match (CTC) Mode
Fast PWM Mode Phase Correct PWM Mode
25

26. Hand Writing Notes: we took it on the previous Lecture
26

27. Request time equation 27

28. Normal Mode
 The simplest mode of operation is the Normal mode (WGM01:0 = 0). In this mode the counting
direction
is always up (incrementing), and no counter clear is performed. The counter simply overruns when
it
passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bottom (0x00). In normal
operation the Timer/Counter Overflow Flag (TOV0) will be set in the same timer clock cycle as
the TCNT0
becomes zero. The TOV0 Flag in this case behaves like a ninth bit, except that it is only set, not
cleared.
However, combined with the timer overflow interrupt that automatically clears the TOV0 Flag, the
timer
resolution can be increased by software. There are no special cases to consider in the Normal
mode, a
new counter value can be written anytime.
The Output Compare unit can be used to generate interrupts at some given time. Using the Output
Compare to generate waveforms in Normal mode is not recommended, since this will occupy too
much of
the CPU time.
28

29. Clear Timer on Compare Match (CTC)
Mode
 In Clear Timer on Compare or CTC mode (WGM01:0 = 2), the OCR0 Register is used to manipulate the
counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT0) matches
the OCR0. The OCR0 defines the top value for the counter, hence also its resolution. This mode allows
greater control of the Compare Match output frequency. It also simplifies the operation of counting
external events.
The timing diagram for the CTC mode is shown in the figure below. The counter value (TCNT0) increases
until a Compare Match occurs between TCNT0 and OCR0, and then counter (TCNT0) is cleared.
29

30. Fast PWM Mode 30

31. Phase Correct PWM Mode, Timing
Diagram
31

32. Timer/Counter Timing Diagrams
No prescaling
With prescaling
32

33. Timer0_Register Description 33

34. 34

35. 35

36. 36

37. 37

38. 38

39. 39

40. 40

41. 41

42. Assignments
Repeat Lab1/2 by using Timer0
42

43. ADC “Analog Digital
Converter”
43

44. ADC introduction
 Signals in the real world are analog: light, sound, you name it.
So, real-world signals must be converted into digital, using a circuit called ADC
(Analog-to-Digital Converter)
44

45. ADC Application: Embedded systems receive
 Embedded systems receive their inputs from the
external world in the form of analog signals.
 An analog signal (amplitude varies continuously)
needs to be converted into a digital signal as
processor only takes digital signals ( a series of
ones and zeros represented by voltages).
 Thus conversions are performed by Analog-to-
Digital(ADC) and the reverse conversion of digital
to analog by Digital-to-Analog(DAC).
45

46. Concepts: Embedded Communication
“PCM”ss Modulation
Analog Modulation Digital Modulation
Continues Wave
Pulse Modulation
AM
FM
PM
PAM
PWM PPM
PCM
46

47. Sampling (Hand writing)
time domain
 Theoretical Sampling: x(t). ð(t-t.)
x(t) Ks(t)
P(t) periodic impulse train
47

48. Sampling (Hand writing) 48

49. Sampling (Hand writing)
Frequency Domain
49

50. quantizer
Vmax
Vmix
50

51. quantizer
Quantizer_max_error =
2
51

52. Quantizer Types
Quantizer
Uniform Quantizer
midrise quantizer midtead quantizer
Non-uniform quantizer
52

53. Simply we can consider ADC as
ADC major characteristics
Conversion Time
Resolution
Vref
Parallel vs. serial
Input channels
Sampler Quantizer Encoder
Analog
Signal
53

54. Resolution
 Resolution is The value of each sampled point will be stored
on a fixed-length variable. If this variable uses eight bits,
this means it can hold values from 0 to 255 (2^8 = 256). If
this variable uses 16 bits, this means it can hold values from
0 to 65,535 (2^16 = 65,536). And so on.
 The signal-to-noise ratio (SNR), which measures the noise
level, can be easily calculated through this formula, where n
is the number of bits used on the ADC:
SNR = 6.02 x n + 1.76 dB
 The higher the SNR, the better. An 8-bit ADC provides a
SNR of 49.9 dB, while a 16-bit SNR provides a SNR of 98
dB (which is, by the way, a virtually no-noise value).
54

55. ADC Types
 Parallel design (also known as Flash ADC);
 Digital-to-Analog Converter-based design
(e.g., ramp counter, successive approximation, tracking);
 Integrator-based design
(e.g., single-slope, dual-slope);
 Sigma-delta design
(also known as delta-sigma, 1-bit ADC or oversampling ADC).
55

56. Parallel Design
The Flash ADC, also called parallel ADC,
It works by comparing the input voltage – i.e., the analog signal – to a
reference voltage,
which would be the maximum value achieved by the analog signal.
For example, if the reference voltage is of 5 volts, this means that the
peak of the analog signal would be 5 volts.
On an 8-bit ADC when the input signal reached 5 volts we would find a
255 (11111111) value on the ADC output, i.e., the maximum value
possible.
Then the voltage reference is lowered through a resistor network and
other comparators added, so the input voltage (analog signal) can be
compared to other values.
56

57. Parallel Design Advantages/disadvantages
 Although Flash ADC uses a very simple design, it requires a lot of components. The
number of required comparers is 2^n-1, where n is the number of output bits. Thus for an eight-
bit Flash ADC 255 comparers would be necessary, and for a 16-bit Flash ADC, 65,535!
 On the other hand, Flash ADC is the fastest ADC type available. The digital equivalent of the
analog signal will be available right away at it output (it will only have the propagation delay
inserted by the logic gates) – hence the name “flash”.
 Another advantage of Flash ADC is that you can create an ADC with non-linear output.
Usually ADCs have a linear output, i.e., each digital number corresponds to a fixed voltage
increase on the analog input. For example, on the 3-bit ADC shown above with a Vref of 5 V,
each digital number would represent 625 mV (5 V / 2^3). So 0 V = 000, 0.625 V = 001,
1.250 V = 010 and so on up to 5 V = 111.
Since Flash ADC comparisons are set by a set of resistors, one could set different values for the
resistors in order to obtain a non-linear output, i.e., one value would represent a different
voltage step from the other values.
57

58. DAC-Based Designs
 There are a few ways to design an ADC using a DAC as part of its comparison
circuit
 Ramp Counter ADC
 Successive Approximation ADC
58

59. Ramp counter ADC
 Ramp counter ADC, also called digital ramp ADC.
Vin is the analog input and Dn through D0 are the digital outputs.
The control line found on the counter turns on the counter when it is
low and stops the counter when it is high.
 The basic idea is to increase the counter until the value found
on the counter matches the value of the analog signal. When
this condition is met, the value on the counter is the digital
equivalent of the analog signal.
 It requires a START pulse for each analog voltage you want to
convert into digital
 So the main problem with this circuit is that it is very slow, as it
would require up to 2^n-1 clock cycles to convert each sample.
For an eight-bit ADC, it would take up to 255 clock cycles to
convert a single sample. For a 16-bit ADC it would take up to
65,535 clock cycles to convert one sample.
59

60. Successive Approximation ADC
 the successive approximation ADC starts first setting the MSB
(most significant bit, on an eight-bit ADC it would be D7). In
order to facilitate the explanations below, consider an eight-
bit ADC.
 The comparison between Vin and the DAC output will tell the
control unit if this bit should remain set at 1 or should be set at
0, as the op amp will tell right away the control unit if the
sample value is greater or lower than 128 (2^7). Then D6 is
set to one, and from the comparison done by the op amp, the
control unit will know if this bit should remain set or not. And so
on.
 The good thing about the successive approximation ADC is its
speed. At the worst case it will find the correct digital value
for the sample at n clock cycles
60

61. Successive Approximation ADC 61

62. Sigma-delta design
 A delta sigma ADC or DAC always consists of a delta sigma modulator which
produces the bitstream and a low pass filter.
Block Diagram of a First Order Digital Delta Sigma
Modulator
62

63. Sigma-delta design
Signals within a First Order
Analog Modulator
63

64. ADC on ATMEGA32
64

65. Major Characteristic of ADC 65

66. ADC Features in Atmega32
 Atmega 16/32 have internal ADC
 8 analogue input channel
 7 differential input channel
 2 differential input channel with 10x or 200x gain
 3 source of Vref
 Internal 2.56V Vref generator
66

67. Interfacing Sensors
•8 channel implies that there are 8 ADC pins are
multiplexed together. You can easily see that these pins
are located across PORTA (PA0…PA7).
•10 bit resolution implies that there are 2^10 = 1024
•the type of ADC implemented inside the AVR MCU is of
Successive Approximation type.
67

68. ADC Prescaler
 There are some predefined division factors – 2, 4, 8, 16, 32, 64, and 128. For
example, a prescaler of 64 implies F_ADC = F_CPU/64. For F_CPU = 16MHz,
F_ADC = 16M/64 = 250kHz.
68

69. Analog to
Digital
Converter
Block
Schematic
Operation
69

70. ADC Registers
70

71. ADMUX – ADC Multiplexer Selection
Register
71

72. ADMUX – ADC Multiplexer Selection
Register
72

73. ADCH and ADCL Data registers
 ADCH:ADCL store the results
of conversion.
 The 10 bit result can be right
or left justified:
ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 - - - - - -ADC9 ADC8
ADCH ADCL
ADLAR = 0
ADLAR =1
ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0- - - - - - ADC9 ADC8
ADCH ADCL

74. ADCSRA – ADC Control and Status
Register A
ADEN – ADC Enable – As the
name says, it enables the ADC
feature. Unless this is enabled,
ADC operations cannot take
place across PORTA i.e. PORTA
will behave as GPIO pins.
ADSC – ADC Start Conversion –
Write this to ‘1’ before starting any
conversion. This 1 is written as long
as the conversion is in progress,
after which it returns to zero.
Normally it takes 13 ADC clock
pulses for this operation. But when
you call it for the first time, it takes
25 as it performs the initialization
together with it.
ADATE – ADC Auto Trigger
Enable – Setting it to ‘1’ enables
auto-triggering of ADC. ADC is
triggered automatically at every
rising edge of clock pulse
ADIF – ADC Interrupt Flag –
Whenever a conversion is
finished and the registers are
updated, this bit is set to ‘1’
automatically
74

75. ADCSRA – ADC Control and Status
Register A
ADIE – ADC Interrupt Enable –
When this bit is set to ‘1’, the
ADC interrupt is enabled. This is
used in the case of interrupt-
driven ADC.
ADPS2:0 – ADC Prescaler
Select Bits – The prescaler
(division factor between XTAL
frequency and the ADC clock
frequency)
75

76. SFIOR – Special Function I/O Register
76

77. Programming ADC 77

78. Why 13 cycles max used for ADC
Conversion time ?
THINK IN-DEPTH 
78

79. Thermistor dependent resistor (DR)
 For example, the following thermistor circuit has a
resistance of 10KΩ at 25°C and a resistance
of 100Ω at 100°C. Calculate the output voltage
(Vout) for both temperatures
79

80. PIR SENSOR:
 The PIR sensor detect only bodies (hot materials and living
objects) in motions not the static ones. This sensor uses Infra red
beam to detect the motion and only covers a certain space
based on the sensor model, you should to go through the
manufacturer datasheet to know about the range. This sensor
module gives only two output states that is logic High 1 which
is equivalent to 3.3 V and logic low 0 equivalent to 0 V.
80

81. GATEWAY CAR Parking
81

82. GATEWAY CAR Parking
 WORKING:
 The PIR sensor is interfaced with Atmega32 AVR
microcontroller to detect the motion around the
environment. Atmega32 considers any voltage
between 2V to 5V as logic high. Hence PIR
sensor is directly interfaced to the input pin of
the controller.
 The circuit shown above will read the status of
the output of the PIR sensor and the ADC will
read the Value if the Value is less than 3 Volt
that mean that the PIR detected the CAR so the
gateway will opened and the 7-segement will
count each car entered on the PARKING and the
Buzzer will run, then the Gateway will closed
after the car moved a way from GATEWAY and
the Buzzer will be OFF.
82

83. References
 http://www.hardwaresecrets.com/how-analog-to-digital-converter-adc-works/3/
 http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html
 AVR Microcontroller and Embedded Systems: Using Assembly and C (Pearson
Custom Electronics Technology) 1st Edition
https://www.amazon.com/AVR-Microcontroller-Embedded-Systems-
Electronics/dp/0138003319
83

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