Introduction to Engineering Electronics

1
Lecture 7 555 Timer

• Energy storage,
• Periodic Waveforms, and
• One of the most useful electronic devices

2
Examples of Physical Periodic Motion

• Pendulum
• Bouncing ball
• Vibrating string (stringed instrument)
• Circular motion (wheel)
• Cantilever beam (tuning fork)

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

4
Daily Average TemperatureAlbany-Troy-Schenectady

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

5
Using Matlab to Produce Audio Signal from Daily
Average Temps

• Data is normalized to mimic sound
• Data is filtered to find fundamental

6
Matlab Window
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

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.

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

10
Charging a Capacitor

• Capacitor Current
• Capacitor Voltage
• Where the time constant

11
Charging a Capacitor

• Note that the voltage rises to a little above 6V
  in 1ms.

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.htm
  l

13
2 Minute QuizName______Section_____Date_____True
or False?

• If C1 take longer to charge C1 than C2

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

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

16
555 Timer

• The capacitor voltage cycles back and forth
  between (2/3)Vcc and (1/3)Vcc at times
  and

17
555 Timer

• The frequency is then given by
• Note the error in the figure

18
Inside the 555

• Note the voltage divider inside the 555 made up
  of 3 equal 5k resistors

19
555 Timer

• These figures are from the lab write up
• Each pin has a name (function)
• Note the divider and other components inside

20
Astable and Monostable Multivibrators

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

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

22
Optical Transmitter Circuit
Astable is used to produce carrier pulses at a
frequency we cannot hear (well above 20kHz)
23
Optical Receiver Circuit

• Receiver circuit for transmitter on previous
  slide

24
2 Minute QuizName______Section_____Date_____True
or False?

• If R1 take longer to charge a given capacitor C through
  R1 than R2

25
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 and triggers relay
  through the transistor

26
555 Timer Applications

• 40 LED bicycle light with 20 LEDs flashing
  alternately at 4.7Hz

27
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

28
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

29
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.

30
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.

31
Tank Circuit Voltage and Current
32
Tank Circuit

• There is a slight decay due to finite wire
  resistance.
• The frequency is given by
• (period is about 10ms)

33
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.

34
2 Minute QuizName______Section_____Date_____True
or False?

• 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.

35
Tank Circuit Application

• In lab 10 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.

36
Disposable Camera Flash Capacitor Connected to a
Small Electromagnet
37
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.

38
Coin Flipper and Can Crusher

• The can crusher device crushes a soda can with a
  magnetic field.

39
Can Crusher and Coin Flipper

• This is an animation a student made as a graphics
  project a few years ago

40
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

41
Magnetic Launchers

• Coilguns/Railguns

42
Coilguns Railguns

• Two types of launchers are being developed for a
  variety of purposes.

43
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.

44
Appendix
45
Using Conservation Laws to Derive Fundamental
Equations

• Energy stored in capacitor plus inductor
• Total energy must be constant, thus

46
Using Conservation Laws

• Simplifying
• This expression will hold if
• Noting that

47
Using Conservation Laws


I
VC
VL

• 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

48
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

49
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

50
Using Conservation Laws

• Simplifying
• Which is satisfied if
• The latter is the relationship for a resistor, so
  the results work.