Lecture 6: 555 Timer - 123seminarsonly.comLecture 6: 555 Timer Energy storage, Periodic Waveforms,...
Transcript of Lecture 6: 555 Timer - 123seminarsonly.comLecture 6: 555 Timer Energy storage, Periodic Waveforms,...
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Lecture 6: 555 Timer
Energy storage,
Periodic Waveforms, and
One of the most useful electronic devices
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Examples of Physical Periodic Motion
• Pendulum
• Bouncing ball
• Vibrating string (stringed instrument)
• Circular motion (wheel)
• Cantilever beam (tuning fork)
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Other Periodic Phenomena
• Daily cycle of solar energy
• Annual cycle of solar energy
• Daily temperature cycle
• Annual temperature cycle
• Monthly bank balance cycle
• Electronic clock pulse trains
• Line voltage and current
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Daily Average Temperature
Albany-Troy-Schenectady
• Data (blue) covers 1995-2002
• Note the sinusoid (pink) fit to the data
-10
0
10
20
30
40
50
60
70
80
90
1
78
15
5
23
2
30
9
38
6
46
3
54
0
61
7
69
4
77
1
84
8
92
5
10
02
10
79
11
56
12
33
13
10
13
87
14
64
15
41
16
18
16
95
17
72
18
49
19
26
20
03
20
80
21
57
22
34
23
11
23
88
24
65
25
42
26
19
26
96
27
73
28
50
Series1
Series2
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Using Matlab to Produce Audio
Signal from Daily Average Temps
0 200 400 600-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8Original data (normalized)
0 200 400 600-0.5
0
0.5Sinusoid fit to data
• Data is normalized to mimic sound
• Data is filtered to find fundamental
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Matlab Window
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Periodic Pulse Train from a 555 Timer
• This circuit puts out a steady state train of
pulses whose timing is determined by the
values of R1, R2 and C1
• The formula has a small error as we will see
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Using Models
• Recall that you should use a model that you understand and/or know how to properly apply
• To use it properly� Check for plausibility of predicted values (ballpark
test). Are the values in a reasonable range?
� Check the rate of changes in the values (checking derivative or slope of plot).
� Are the most basic things satisfied?• Conservation of energy, power, current, etc.
• Developing a qualitative understanding of phenomena now will help later and with simulations.
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Charging a Capacitor
• Capacitor C1 is charged up by current flowing through R1
• As the capacitor charges up, its voltage increases and the current charging it decreases, resulting in the charging rate shown
VV V
R1
1k
U2
TOPEN = 0
12
C1
1uF
U1
TCLOSE = 0
1 2
0
V1
10V
IV V
R
V
k
CAPACITOR CAPACITOR=−
=−1
1
10
1
Ti me
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msV( U2: 1) V( R1: 2) V( V1: +)
0V
2V
4V
6V
8V
10V
Capaci t or Vol t age
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Charging a Capacitor
• Capacitor Current
• Capacitor Voltage
• Where the time constant
Ti me
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msI ( R1) I ( C1)
0A
2mA
4mA
6mA
8mA
10mA
Capaci t or and Resi st or Cur r ent
Ti me
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msV( U2: 1) V( R1: 2) V( V1: +)
0V
2V
4V
6V
8V
10V
Capaci t or Vol t age
I I eo
t
=−
τ
V V eo
t
= −
−1 τ
τ = = ⋅ =RC R C ms1 1 1
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Charging a Capacitor
• Note that the voltage rises to a little above 6V in 1ms.
Ti me
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msV( U2: 1) V( R1: 2) V( V1: +)
0V
2V
4V
6V
8V
10V
Capaci t or Vol t age
( ) .1 6321
− =−
e
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Charging a Capacitor
• There is a good description of capacitor
charging and its use in 555 timer circuits at http://www.uoguelph.ca/~antoon/gadgets/555/555.html
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2 Minute Quiz
Name___________
Section___
True or False?
• If C1 < C2, for a fixed charging current, it will
take longer to charge C1 than C2
• If R1 < R2, for a fixed charging voltage, it will
take longer to charge a given capacitor C
through R1 than R2
• When a capacitor C is connected to a battery
through a resistor R, the charging current will
be a maximum at the moment the connection
is made and decays after that.
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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555 Timer
• At the beginning of the cycle, C1 is charged through resistors R1 and R2. The charging time constant is
• The voltage reaches (2/3)Vcc in a time
τ = +( )R R C1 2 1
τ = +0 693 1 2 1. ( )R R C
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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555 Timer
• When the voltage on the capacitor reaches (2/3)Vcc, a switch is closed at pin 7 and the capacitor is discharged to (1/3)Vcc, at which time the switch is opened and the cycle starts over
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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555 Timer
• The capacitor voltage cycles back and forth between (2/3)Vcc and (1/3)Vcc at times and τ
10 693 1 2 1= +. ( )R R C
τ2
0 693 2 1= . ( )R C
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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555 Timer
• The frequency is then given by
Note the error in the figure
fR R C R R C
=+ ⋅
=+ ⋅
1
0 693 1 2 2 1
144
1 2 2 1. ( )
.
( )
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Inside the 555
• Note the voltage divider inside the 555 made up of 3 equal 5k resistors
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555 Timer
• These figures are from the lab writeup
• Each pin has a name (function)
• Note the divider and other components inside
NE555
2
5
3
7
6
4 81
TR
CV
Q
DIS
THR
R
VC
CG
ND
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Astable and Monostable Multivibrators
• Astable puts out a continuous sequence of pulses
• Monostable puts out one pulse each time the switch is connected
5V
Ra
C
0.0
1uF
LED
NE555
2
5
3
7
6
4 81
TR
CV
Q
DIS
THR
R
VC
CG
ND
Rb
5V
12
1K
0.0
1u
F
C
R
LED
NE555
2
5
3
7
6
4 81
TR
CV
Q
DIS
THR
R
VC
CG
ND
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Astable and Monostable Multivibrators
• What are they good for?
� Astable: clock, timing signal
� Monostable: a clean pulse of the correct
height and duration for digital system
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Optical Transmitter Circuit
Astable is used to produce carrier pulses at a
frequency we cannot hear (well above 20kHz)
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Optical Receiver Circuit
• Receiver circuit for transmitter on previous slide
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Clapper Circuit
• Signal is detected by microphone
• Clap is amplified by 741 op-amp
• Ugly clap pulse triggers monostable to produce clean digital pulse
• Counter counts clean pulses to 2 and triggers relay through the transistor
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555 Timer Applications
• 40 LED bicycle light with 20 LEDs flashing alternately at 4.7Hz
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555 Timer Applications
• 555 timer is used to produce an oscillating signal whose voltage output is increased by the transformer to a dangerous level, producing sparks. DO NOT DO THIS WITHOUT SUPERVISION
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Tank Circuit: A Classical Method Used to Produce an Oscillating Signal
• A Tank Circuit is a combination of a capacitor and an inductor
• Each are energy storage devices
W W LIM L= =1
2
2 W W CVE C= =1
2
2
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Tank Circuit: How Does It Work?
• Charge capacitor to 10V. At this point, all of the energy is in the capacitor.
• Disconnect voltage source and connect capacitor to inductor.
• Charge flows as current through inductor until capacitor voltage goes to zero. Current is then maximum through the inductor and all of the energy is in the inductor.
0
V1
10V
U2
TCLOSE = 0
1 2U1
TOPEN = 0
1 2
C1
1uF
V
L1
10uH
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Tank Circuit
• The current in the inductor then recharges the capacitor until the cycle repeats.
• The energy oscillates between the capacitor and the inductor.
• Both the voltage and the current are sinusoidal.
0
V1
10V
U2
TCLOSE = 0
1 2U1
TOPEN = 0
1 2
C1
1uF
V
L1
10uH
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Tank Circuit Voltage and Current
Ti me
0s 10us 20us 30us 40us 50us 60us 70us 80us 90us 100usV( C1: 1)
- 10V
0V
10V
SEL>>
Vol t age
I ( L1)- 4. 0A
0A
4. 0A
Cur r ent
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Tank Circuit
• There is a slight decay due to finite wire resistance.
• The frequency is given by
(period is about 10ms)
Ti me
0s 10us 20us 30us 40us 50us 60us 70us 80us 90us 100usV( C1: 1)
- 10V
0V
10V
SEL>>
Vol t age
I ( L1)- 4. 0A
0A
4. 0A
Cur r ent
fLC
=1
2π
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Tank Circuit
•Tank circuits are the basis of most oscillators. If
such a combination is combined with an op-amp,
an oscillator that produces a pure tone will result.
•This combination can also be used to power an
electromagnet.
•Charge a capacitor
•Connect the capacitor to an electromagnet
(inductor). A sinusoidal magnetic field will
result.
•The magnetic field can produce a magnetic
force on magnetic materials and conductors.
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Tank Circuit Application
• In lab 9 we will be using the circuit from a disposable camera.
• We can also use this type of camera as a power source for an electromagnet.
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Disposable Camera Flash Capacitor Connected to a Small Electromagnet
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Disposable Camera Flash Experiment/Project
• A piece of a paperclip is placed part way into the
electromagnet.
• The camera capacitor is charged and then triggered to
discharge through the electromagnet (coil).
• The large magnetic field of the coil attracts the paperclip to
move inside of the coil.
• The clip passes through the coil, coasting out the other side
at high speed when the current is gone.
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Coin Flipper and Can Crusher
• The can crusher device (not presently in operation) crushes a soda can with a magnetic field.
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Can Crusher and Coin Flipper
• This is an animation a student made as a graphics project a few years ago
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Can Crusher and Coin Flipper
• For both the can crusher and coin flipper, the coil fed
by the capacitor acts as the primary of a transformer.
• The can or the coin acts as the secondary.
• A large current in the primary coil produces an even
larger current in the can or coin (larger by the ratio of
the turns in the primary coil)
• The current in the coin or can is such that an
electromagnet of the opposite polarity is formed
(Lenz’ Law) producing two magnets in close proximity
with similar poles facing one another.
• The similar poles dramatically repel one another
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Magnetic Launchers
• Coilguns/Railguns
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Coilguns & Railguns
• Two types of launchers are being developed for a variety of purposes.
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Where Will You See This Material Again?
• Electromagnetic Fields and Forces: Fields and Waves I
• 555 Timers: Many courses including Analog Electronics and Digital Electronics
• Oscillators: Analog electronics
• Clocks, etc: Digital Electronics, Computer Components and Operations, and about half of the ECSE courses.
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Appendix
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Using Conservation Laws to Derive
Fundamental Equations
• Energy stored in capacitor plus inductor
• Total energy must be constant, thus
Energy W LI CVTOTAL= = +1
2
1
2
2 2
dW
dtL I
dI
dtC V
dV
dt
TOTAL = = +01
22
1
22
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Using Conservation Laws
• Simplifying
• This expression will hold if
• Noting that
dW
dtL
dI
dtI C
dV
dtVTOTAL L
LC
C= = +0
V LdI
dtL
L= I CdV
dtC
C=
V VC L= − I IC L=
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Using Conservation Laws
• Note that for the tank circuit� The same current I flows through both
components
� The convention is that the current enters the higher voltage end of each component
I
+
+
VC
VL
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Using Conservation Laws
• Experimentally, it was also determined that the current-voltage relationship for a capacitor is
• Experimentally, it was also determined that the current-voltage relationship for an inductor is
I CdV
dtC
C=
V LdI
dtL
L=
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Using Conservation Laws
• Applying the I-V relationship for a capacitor to the expressions we saw before for charging a capacitor through a resistor
• We see that
I I eo
t
=−
τ V V eo
t
= −
−1 τI C
dV
dtC
C=
( )I I e CdV
dtCV eC o
tC
o
t
= = = − −
− −τ τ
τ0 1
February 8, 2009 Introduction to Engineering ElectronicsK. A. Connor
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Using Conservation Laws
• Simplifying
• Which is satisfied if
• The latter is the relationship for a resistor, so the results work.
( )I I e CdV
dtCV eC o
tC
o
t
= = =
− −τ τ
τ1
τ = RC IV
Ro
o=