1. Lecture 7: 555 Timer Energy storage, Periodic Waveforms, and
One of the most useful electronic devices
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2. Examples of Physical Periodic Motion
Pendulum
Bouncing ball
Vibrating string (stringed instrument)
Circular motion (wheel)
Cantilever beam (tuning fork)
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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
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4. Daily Average Temperature Albany-Troy-Schenectady
Data (blue) covers
Note the sinusoid (pink) fit to the data
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5. Using Matlab to Produce Audio Signal from Daily Average Temps
Data is normalized to mimic sound
Data is filtered to find fundamental
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6. Introduction to Engineering Electronics
Matlab Window
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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
Introduction to Engineering Electronics
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8. Introduction to Engineering Electronics
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.
Introduction to Engineering Electronics
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9. Introduction to Engineering Electronics
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
Introduction to Engineering Electronics
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10. Introduction to Engineering Electronics
Charging a Capacitor
Capacitor Current
Capacitor Voltage
Where the time constant
Introduction to Engineering Electronics
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11. Introduction to Engineering Electronics
Charging a Capacitor
Note that the voltage rises to a little above 6V in 1ms.
Introduction to Engineering Electronics
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12. Introduction to Engineering Electronics
Charging a Capacitor
There is a good description of capacitor charging and its use in 555 timer circuits at
Introduction to Engineering Electronics
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13. 2 Minute Quiz Name______Section_____Date_____ True or False?
If C1 < C2, for a fixed charging current, it will take longer to charge C1 than C2
Introduction to Engineering Electronics
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14. Introduction to Engineering Electronics
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
Introduction to Engineering Electronics
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15. Introduction to Engineering Electronics
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
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16. Introduction to Engineering Electronics
555 Timer
The capacitor voltage cycles back and forth between (2/3)Vcc and (1/3)Vcc at times and
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17. Introduction to Engineering Electronics
555 Timer
The frequency is then given by
Note the error in the figure
Introduction to Engineering Electronics
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18. Introduction to Engineering Electronics
Inside the 555
Note the voltage divider inside the 555 made up of 3 equal 5k resistors
Introduction to Engineering Electronics
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19. Introduction to Engineering Electronics
555 Timer
These figures are from the lab write up
Each pin has a name (function)
Note the divider and other components inside
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20. Astable and Monostable Multivibrators
Astable puts out a continuous sequence of pulses
Monostable puts out one pulse each time the switch is connected
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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
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22. Optical Transmitter Circuit
Astable is used to produce carrier pulses at a frequency we cannot hear (well above 20kHz)
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23. Optical Receiver Circuit
Receiver circuit for transmitter on previous slide
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24. 2 Minute Quiz Name______Section_____Date_____ True or False?
If R1 < R2, for a fixed charging voltage, it will take longer to charge a given capacitor C through R1 than R2
Introduction to Engineering Electronics
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25. Introduction to Engineering Electronics
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
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26. Introduction to Engineering Electronics
555 Timer Applications
40 LED bicycle light with 20 LEDs flashing alternately at 4.7Hz
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27. Introduction to Engineering Electronics
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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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
Introduction to Engineering Electronics
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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.
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30. Introduction to Engineering Electronics
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.
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31. Tank Circuit Voltage and Current
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32. Introduction to Engineering Electronics
Tank Circuit
There is a slight decay due to finite wire resistance.
The frequency is given by
(period is about 10ms)
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33. Introduction to Engineering Electronics
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.
Introduction to Engineering Electronics
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34. 2 Minute Quiz Name______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.
Introduction to Engineering Electronics
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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.
Introduction to Engineering Electronics
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36. Disposable Camera Flash Capacitor Connected to a Small Electromagnet
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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.
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38. Coin Flipper and Can Crusher
The can crusher device crushes a soda can with a magnetic field.
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39. Can Crusher and Coin Flipper
This is an animation a student made as a graphics project a few years ago
Introduction to Engineering Electronics
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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
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41. Introduction to Engineering Electronics
Magnetic Launchers
Coilguns/Railguns
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42. Introduction to Engineering Electronics
Coilguns & Railguns
Two types of launchers are being developed for a variety of purposes.
Introduction to Engineering Electronics
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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.
Introduction to Engineering Electronics
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44. Introduction to Engineering Electronics
Appendix
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45. Using Conservation Laws to Derive Fundamental Equations
Energy stored in capacitor plus inductor
Total energy must be constant, thus
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46. Using Conservation Laws
Simplifying
This expression will hold if
Noting that
Introduction to Engineering Electronics
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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
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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
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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
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50. Using Conservation Laws
Simplifying
Which is satisfied if
The latter is the relationship for a resistor, so the results work.
Introduction to Engineering Electronics
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