April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
1
Lecture 6: 555 Timer
Energy storage,Periodic Waveforms, and
One of the most useful electronic devices
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
2
Examples of Physical Periodic Motion
• Pendulum• Bouncing ball• Vibrating string (stringed instrument)• Circular motion (wheel)• Cantilever beam (tuning fork)
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
3
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
4
Daily Average TemperatureAlbany-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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
5
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
6
Matlab Window
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
7
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
8
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.
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
9
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
V110V
IV V
R
V
kCAPAC ITO R CAPAC ITO R
1
1
10
1
Time
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msV(U2:1) V(R1:2) V(V1:+)
0V
2V
4V
6V
8V
10V
Capacitor Voltage
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
10
Charging a Capacitor
• Capacitor Current
• Capacitor Voltage
• Where the time constant
Time
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msI(R1) I(C1)
0A
2mA
4mA
6mA
8mA
10mA
Capacitor and Resistor Current
Time
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msV(U2:1) V(R1:2) V(V1:+)
0V
2V
4V
6V
8V
10V
Capacitor Voltage
I I eot
V V eo
t
1
RC R C m s1 1 1
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
11
Charging a Capacitor
• Note that the voltage rises to a little above 6V in 1ms.
Time
0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msV(U2:1) V(R1:2) V(V1:+)
0V
2V
4V
6V
8V
10V
Capacitor Voltage
( ) .1 6321 e
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
12
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
13
2 Minute QuizName___________
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.
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
14
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
( )R R C1 2 1
0 693 1 2 1. ( )R R C
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
15
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
16
555 Timer
• The capacitor voltage cycles back and forth between (2/3)Vcc and (1/3)Vcc at times and
1 0 693 1 2 1 . ( )R R C 2 0 693 2 1 . ( )R C
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
17
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
1 44
1 2 2 1. ( )
.
( )
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
18
Inside the 555
• Note the voltage divider inside the 555 made up of 3 equal 5k resistors
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
19
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
20
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
0.01
uF
LED
NE555
2
5
3
7
6
4 81
TR
CV
Q
DIS
THR
R
VC
CG
ND
Rb
5V
12
1K
0.01
uFC
R
LED
NE555
2
5
3
7
6
4 81
TR
CV
Q
DIS
THR
R
VC
CG
ND
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
21
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
22
Optical Transmitter Circuit
Astable is used to produce carrier pulses at a frequency we cannot hear (well above 20kHz)
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
23
Optical Receiver Circuit
• Receiver circuit for transmitter on previous slide
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
24
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
25
555 Timer Applications
• 40 LED bicycle light with 20 LEDs flashing alternately at 4.7Hz
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
26
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
27
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
22 W W CVE C
1
22
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
28
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
V110V
U2
TCLOSE = 0
1 2U1
TOPEN = 0
1 2
C1
1uF
V
L1
10uH
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
29
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
V110V
U2
TCLOSE = 0
1 2U1
TOPEN = 0
1 2
C1
1uF
V
L1
10uH
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
30
Tank Circuit Voltage and Current
Time
0s 10us 20us 30us 40us 50us 60us 70us 80us 90us 100usV(C1:1)
-10V
0V
10V
SEL>>
Voltage
I(L1)-4.0A
0A
4.0A
Current
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
31
Tank Circuit
• There is a slight decay due to finite wire resistance.
• The frequency is given by (period is about 10ms)
Time
0s 10us 20us 30us 40us 50us 60us 70us 80us 90us 100usV(C1:1)
-10V
0V
10V
SEL>>
Voltage
I(L1)-4.0A
0A
4.0A
Current
fLC
1
2
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
32
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.
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
33
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.
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
34
Disposable Camera Flash Capacitor Connected to a Small Electromagnet
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
35
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.
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
36
Coin Flipper and Can Crusher
• The can crusher device (not presently in operation) crushes a soda can with a magnetic field.
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
37
Can Crusher and Coin Flipper
• This is an animation a student made as a graphics project a few years ago
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
38
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
39
Magnetic Launchers
• Coilguns/Railguns
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
40
Coilguns & Railguns
• Two types of launchers are being developed for a variety of purposes.
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
41
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.
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
42
Appendix
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
43
Using Conservation Laws to Derive Fundamental Equations
• Energy stored in capacitor plus inductor
• Total energy must be constant, thus
Energy W LI CVTO TAL 1
2
1
22 2
dW
dtL I
d I
d tC V
dV
d tTO TAL 0
1
22
1
22
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
44
Using Conservation Laws
• Simplifying
• This expression will hold if
• Noting that
dW
dtLd I
d tI C
dV
d tVTO TAL L
LC
C 0
V LdI
d tLL I C
dV
d tCC
V VC L I IC L
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
45
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
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
46
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
d tCC
V LdI
d tLL
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
47
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 eot
V V eo
t
1 I C
dV
d tCC
I I e CdV
d tCV eC o
tC
o
t
0 1
April 12, 2023
Introduction to Engineering Electronics
K. A. Connor
48
Using Conservation Laws
• Simplifying
• Which is satisfied if
• The latter is the relationship for a resistor, so the results work.
I I e CdV
d tCV eC o
tC
o
t
1
RC IV
Roo