555 Timer

Lecture 6: 555 Timer Energy storage, Periodic Waveforms, and One of the most useful electronic devices February 8, 2009

Introduction to Engineering Electronics K. A. Connor

1

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 Electronics K. 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 Electronics K. A. Connor

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Daily Average Temperature Albany-Troy-Schenectady 90 80 70 60 50 Series1 Series2

40 30 20 10 2850

2773

2696

2619

2542

2465

2388

2311

2234

2157

2080

2003

1926

1849

1772

1695

1618

1541

1464

1387

1310

1233

1156

1079

1002

925

848

771

694

617

540

463

386

309

232

155

-10

78

1

0

• Data (blue) covers 1995-2002 • Note the sinusoid (pink) fit to the data February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Using Matlab to Produce Audio Signal from Daily Average Temps Original data (normalized)

Sinusoid fit to data

0.8

0.5

0.6 0.4 0.2 0 0 -0.2 -0.4 -0.6 -0.8 -1

0

200

400

600

-0.5

0

200

400

600

• Data is normalized to mimic sound • Data is filtered to find fundamental February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Matlab Window

February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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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 February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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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 Electronics K. A. Connor

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Charging a Capacitor 10V

TCLOSE = 0 1 U1

R1

2 8V

V

V

1

V

1k

6V

U2

V1

TOPEN = 0 2

10V

Capaci t or Vol t age

C1 1uF

4V

2V

0V 0s

0

V( U2: 1)

1ms V( R1: 2)

2ms V( V1: +)

3ms

4ms

5ms

6ms

7ms

8ms

9ms

10ms

Ti me

• Capacitor C1 is charged up by current flowing through R1 V 1 − VCAPACITOR 10 − VCAPACITOR I=

R1

=

1k

• As the capacitor charges up, its voltage increases and the current charging it decreases, resulting in the charging rate shown February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Charging a Capacitor 10mA

10V

8mA

8V

6mA

6V

Capaci t or and Resi st or Cur r ent

Capaci t or Vol t age

4mA

4V

2mA

2V

0A 0s I ( R1)

1ms I ( C1)

2ms

3ms

4ms

5ms

6ms

7ms

8ms

9ms

10ms

0V 0s V( U2: 1)

1ms V( R1: 2)

2ms V( V1: +)

3ms

4ms

Ti me

5ms

6ms

7ms

8ms

9ms

10ms

Ti me

• Capacitor Current • Capacitor Voltage

I = Ioe

− tτ

V = Vo 1 − e

− tτ

 

• Where the time constant τ = RC = R1 ⋅ C1 = 1ms February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Charging a Capacitor 10V

8V

6V Capaci t or Vol t age

4V

2V

0V 0s V( U2: 1)

1ms V( R1: 2)

2ms V( V1: +)

3ms

4ms

5ms

6ms

7ms

8ms

9ms

10ms

Ti me

• Note that the voltage rises to a little above 6V in 1ms. (1 − e − 1 ) =.632 February 8, 2009

Introduction to Engineering Electronics K. 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

February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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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 Electronics K. 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 τ = ( R1 + R2)C1 • The voltage reaches (2/3)Vcc in a time τ = 0.693( R1 + R2)C1 February 8, 2009

Introduction to Engineering Electronics K. 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 Electronics K. 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 τ 1 = 0.693( R1 + R2)C1 and τ 2 = 0.693( R2)C1 February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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555 Timer

• The frequency is then given by 1 144 . f = = 0.693( R1 + 2 ⋅ R2)C1 ( R1 + 2 ⋅ R2)C1 Note the error in the figure February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Inside the 555

• Note the voltage divider inside the 555 made up of 3 equal 5k resistors February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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DIS

8 VCC

7

R

4

555 Timer

6 2 5

THR TR CV

3

GND

Q

1

NE555

• These figures are from the lab writeup • Each pin has a name (function) • Note the divider and other components inside February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Astable and Monostable Multivibrators 5V

8 VCC

4 5

NE555

C

THR TR CV

GND

LED

3

LED

NE555 1

GND

CV

Q 6 2

1

0.01uF

5

THR TR

3

1

6 2

DIS

1K

0.01uF

Q

R

7

2

DIS

Rb

C

R

VCC

7

R

4

Ra

8

5V

• Astable puts out a continuous sequence of pulses • Monostable puts out one pulse each time the switch is connected February 8, 2009

Introduction to Engineering Electronics K. 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 Electronics K. 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 Electronics K. A. Connor

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Optical Receiver Circuit

• Receiver circuit for transmitter on previous slide February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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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 February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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555 Timer Applications

• 40 LED bicycle light with 20 LEDs flashing alternately at 4.7Hz February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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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 February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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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 1 1 2 2 WE = WC = CV WM = WL = LI 2 2 February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Tank Circuit: How Does It Work? TOPEN = 0

TCLOSE = 0

1 U1

1 U2

2

2

V

V1

L1

10V C1

10uH

1uF

0

• 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. February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Tank Circuit TOPEN = 0

TCLOSE = 0

1 U1

1 U2

2

2

V

V1

L1

10V C1

10uH

1uF

0

• 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. February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Tank Circuit Voltage and Current 4. 0A Cur r ent

0A

- 4. 0A I ( L1) 10V Vol t age

0V

SEL>> - 10V 0s

10us

20us

30us

40us

50us

60us

70us

80us

90us

V( C1: 1) Ti me

February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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100us

Tank Circuit 4. 0A Cur r ent

0A

- 4. 0A I ( L1) 10V Vol t age

0V

SEL>> - 10V 0s

10us

20us

30us

40us

50us

60us

70us

80us

90us

100us

V( C1: 1) Ti me

• There is a slight decay due to finite wire resistance. 1 • The frequency is given by f = 2π LC (period is about 10ms) February 8, 2009

Introduction to Engineering Electronics K. 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 Electronics K. 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 Electronics K. A. Connor

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Disposable Camera Flash Capacitor Connected to a Small Electromagnet

February 8, 2009

Introduction to Engineering Electronics K. 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 Electronics K. 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 Electronics K. 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 Electronics K. 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 Electronics K. A. Connor

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Magnetic Launchers

• Coilguns/Railguns February 8, 2009

Introduction to Engineering Electronics K. 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 Electronics K. 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 Electronics K. A. Connor

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Appendix

February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Using Conservation Laws to Derive Fundamental Equations • Energy stored in capacitor plus inductor Energy = WTOTAL

1 2 1 = LI + CV 2 2 2

• Total energy must be constant, thus dWTOTAL 1 dI 1 dV = 0 = L2 I + C 2V 2 dt dt 2 dt

February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Using Conservation Laws • Simplifying dWTOTAL dI L dVC =0=L IL + C VC dt dt dt

• This expression will hold if dI L VL = L dt

dVC IC = C dt

• Noting that VC = −VL February 8, 2009

IC = I L

Introduction to Engineering Electronics K. A. Connor

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Using Conservation Laws I + VL VC

+

• 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 February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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Using Conservation Laws • Experimentally, it was also determined that the current-voltage relationship for dVC a capacitor is IC = C dt • Experimentally, it was also determined that the current-voltage relationship for an inductor is dI L

VL = L

February 8, 2009

dt

Introduction to Engineering Electronics K. A. Connor

46

Using Conservation Laws • Applying the I-V relationship for a capacitor to the expressions we saw before for charging a capacitor through a resistor t − − tτ dVC V = Vo 1 − e τ  IC = C I = Ioe dt • We see that

IC = Ioe February 8, 2009

−t

τ

dVC −t   =C = CVo  0 − − 1τ e τ  dt

(

Introduction to Engineering Electronics K. A. Connor

)

47

Using Conservation Laws • Simplifying

dV −t  C  IC = Ioe τ = C = CVo  1 e τ  τ dt • Which is satisfied if −t

τ = RC

( )

Vo Io = R

• The latter is the relationship for a resistor, so the results work. February 8, 2009

Introduction to Engineering Electronics K. A. Connor

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