1. Investigating Basic Circuits Post-Activity Discussion
General Safety
Digital Electronics TM
1.1 Foundations and The Board Game Counter
Investigating Basic Circuits
Post-Activity Discussion
Digital Electronics
© 2014 Project Lead The Way, Inc.
Project Lead The Way, Inc.
Copyright 2009

2. This Presentation Will…
Circuit Theory Laws
This Presentation Will…
Digital Electronics TM
1.2 Introduction to Analog
Answers the following questions:
What are some of the basic components that make up simple circuits and what do they do?
What are the important characteristics of a circuit and how do I measure different parts of a circuit?
How do I work safely with circuits?
How do I measure voltage in a circuit?
How does the arrangement of components affect the characteristics of the circuit?
How can I use calculations to design circuits before I start creating one?
Introductory Slide / Overview of Presentation
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Copyright 2009

3. Light Emitting Diode (LED)
Circuit Theory Laws
Light Emitting Diode (LED)
Digital Electronics TM
1.2 Introduction to Analog
In Activity Investigating Basic Circuits you created a simple circuit similar to the one shown below.
With the circuit active, what happened when you flipped the LED in the opposite direction?
The LED will not light up.
What does that tell you about LEDs (a type of diode)?
They are semiconductors that only work in one direction.
Introductory Slide / Overview of Presentation
Project Lead The Way, Inc.
Copyright 2009

4. Circuit Theory Laws
Resistors
Digital Electronics TM
1.2 Introduction to Analog
What do you think the role of the resistor is in the circuit?
The resistor protects the LED by limiting the flow of current through it.
Resistor - Component made of material that opposes flow of current and therefore has some value of resistance.
Introductory Slide / Overview of Presentation
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Copyright 2009

5. How to Properly Use a DMM
Circuit Theory Laws
How to Properly Use a DMM
Digital Electronics TM
1.2 Introduction to Analog
What happened when you switched the leads?
Everyone read slightly different values. Why?
The DMM still reads the voltage, it is just negative.
Tolerances of components.
The voltage sources are slightly different.
5 V
- 5 V
Introduction to the three basic elements of electricity/electronics
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6. How to Properly Use a DMM
Circuit Theory Laws
How to Properly Use a DMM
Digital Electronics TM
1.2 Introduction to Analog
How do you ensure the best precision in reading voltage with the DMM? (most significant figures)
The DMM reading becomes more precise by a factor of ten each time the voltage range is decreased.
Range Reading
600V-0V 005V (1 s.f.)
20V-0V 4.7V (2 s.f.)
2V-0V 1 or +Over
Introduction to the three basic elements of electricity/electronics
Why was there no reading at 2V-0V?
The range is too small.
2V-0V range cannot measure 4.7V.
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7. Circuit Theory Laws
What is Voltage?
Digital Electronics TM
1.2 Introduction to Analog
Now that you can measure it, let’s explore what voltage is in more detail.
Voltage is the electrical force that causes current to flow in a circuit. It is measured in VOLTS.
This force can be created by separating charges.
Voltage has been described many different ways as the science around electricity has evolved.
We will describe voltage by looking at another common component in electronics called a capacitor.
The formal definition of voltage and the scientist that bears their name.
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8. Circuit Theory Laws
Capacitors
Digital Electronics TM
1.2 Introduction to Analog
A capacitor is an electronic component that can be used to store an electrical charge.
A capacitor can be thought of as a temporary battery.
Introduction to the three basic elements of electricity/electronics - +
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9. What is Voltage? Example: Parallel Plate Capacitor
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Example:
Parallel Plate Capacitor
A battery pushes charge onto opposite plates which generates an electric field.
Theoretically, a positive test charge placed in the field has the potential to move.
Can you guess which way the test charge would move in this electric field? +
Test Charge
The formal definition of voltage and the scientist that bears their name. - +
Good guess! The test charge has the potential to move left.
(opposites attract)
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10. What is Voltage? Example Parallel Plate Capacitor
Circuit Theory Laws
What is Voltage?
Digital Electronics TM
1.2 Introduction to Analog
Example
Parallel Plate Capacitor
If a conductor were to touch both plates, all the charges one would move to the other.
This can create a lot of current!
Be careful when dealing with high voltage capacitors.
Someone will think the lightning bolt is going in the wrong direction. - +
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11. Voltage Source: Battery
Circuit Theory Laws
Voltage Source: Battery
Digital Electronics TM
1.2 Introduction to Analog
A battery is a device that converts chemical energy into electrical energy.
The chemical reaction provides more charges for a longer time than a capacitor does.
One side of a battery has the potential to do work
(12V) High Potential (right side of battery)
One side of a battery has no potential to do work
(0V) Low Potential or Ground (left side of battery)
The battery would make both test charges move to the right.
Introduction to the three basic elements of electricity/electronics +
Test Charge B - + +
Test Charge A
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12. Circuit Theory Laws
What is Voltage?
Digital Electronics TM
1.2 Introduction to Analog
In order for a charge to move, there must be a separation of charge or a potential difference across two points in the circuit. Voltage is defined mathematically as ΔV = V final – V initial A Volt(V) is a Joule(J) of work per Coulomb (C) of charge. 1V = 1J 1C A 12V battery is able to do 12 Joules of work for every 1 Coulomb of charge the battery can provide.
Introduction to the three basic elements of electricity/electronics
Project Lead The Way, Inc.
Copyright 2009

13. Circuit Theory Laws
What is Voltage?
Digital Electronics TM
1.2 Introduction to Analog
Both of these situations read zero volts on the DMM. Why?
Introduction to the three basic elements of electricity/electronics
(6a) (6b)
There is no separation of charge. For each of these arrangements, the potential difference or voltage across the test points is zero.
(6a) ΔV = 5V-5V=0
(6b) ΔV = 0V-0V=0
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14. Circuit Theory Laws
Current: An Analogy
Digital Electronics TM
1.2 Introduction to Analog
The flow of water from one tank to another is a good analogy for an electrical circuit and the mathematical relationship between voltage, resistance, and current.
Force: The difference in the water levels ≡ Voltage
Flow: The flow of the water between the tanks ≡ Current
Opposition: The valve that limits the amount of water ≡ Resistance
The classic water analogy for voltage/current/resistance.
Force
Flow
Opposition
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15. Anatomy of a Flashlight
Circuit Theory Laws
Anatomy of a Flashlight
Digital Electronics TM
1.2 Introduction to Analog
D - Cell
Switch
Switch
Light
Bulb
Light
Bulb
This slide shows an everyday object (flashlight), its block diagram, and the equivalent schematic.
Battery
Battery
Block Diagram
Schematic Diagram
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16. Flashlight Schematic Closed circuit (switch closed) Current flow
Circuit Theory Laws
Flashlight Schematic
Digital Electronics TM
1.2 Introduction to Analog
Current
Resistance
Voltage
Closed circuit (switch closed)
Current flow
Lamp is on
Lamp is resistance, uses energy to produce light (and heat)
Open circuit (switch open)
No current flow
Lamp is off
Lamp is resistance, but is not using any energy
This slide shows the flow of electrons (not really; it’s the flow of current see the next slide) when the switch closed.
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17. Circuit Theory Laws
Current Flow
Digital Electronics TM
1.2 Introduction to Analog
Conventional Current assumes that current flows out of the positive side of the battery, through the circuit, and back to the negative side of the battery. This was the convention established when electricity was first discovered, but it is incorrect!
Electron Flow is what actually happens. The electrons flow out of the negative side of the battery, through the circuit, and back to the positive side of the battery.
Conventional
Current
Conventional Current vs. Electron Flow (Scientists vs. Engineers – since this is an engineering course, guess who wins?).
Electron
Flow
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18. Engineering vs. Science
Circuit Theory Laws
Engineering vs. Science
Digital Electronics TM
1.2 Introduction to Analog
The direction that the current flows does not affect what the current is doing; thus, it doesn’t make any difference which convention is used as long as you are consistent.
Both Conventional Current and Electron Flow are used. In general, the science disciplines use Electron Flow, whereas the engineering disciplines use Conventional Current.
Since this is an engineering course, we will use Conventional Current.
Of course, the engineers win!
Electron
Flow
Conventional
Current
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Copyright 2009

19. Circuit Theory Laws
Ohm’s Law
Digital Electronics TM
1.2 Introduction to Analog
Defines the relationship between voltage, current, and resistance in an electric circuit
Ohm’s Law:
Current in a resistor varies in direct proportion to the voltage applied to it and is inversely proportional to the resistor’s value.
Stated mathematically: V I R
Introduction to Ohm’s Law
Where: I is the current (amperes)
V is the potential difference (volts)
R is the resistance (ohms)
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20. Ohm’s Law Triangle V I R V I R V I R Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog V I R V I R
Ohm’s Law Triangle – Place your finger over the unknown quantity and what remains is the equation used to solve for the unknown. V I R
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21. Example: Ohm’s Law Example:
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Example:
The flashlight shown uses a 6 volt battery and has a bulb with a resistance of 150 . When the flashlight is on, how much current will be drawn from the battery?
VT = + - VR IR
Schematic Diagram
Pause the presentation and allow the student to work on the example. The solution is on the next slide.
Project Lead The Way, Inc.
Copyright 2009

22. Example: Ohm’s Law Example:
Circuit Theory Laws
Example: Ohm’s Law
Digital Electronics TM
1.2 Introduction to Analog
Example:
The flashlight shown uses a 6 volt battery and has a bulb with a resistance of 150 . When the flashlight is on, how much current will be drawn from the battery?
Solution:
VT = + - VR IR
Schematic Diagram V I R
This slide provides the solution. If you print handouts, do not print this page.
Project Lead The Way, Inc.
Copyright 2009

23. Circuit Configuration
Circuit Theory Laws
Circuit Configuration
Digital Electronics TM
1.2 Introduction to Analog
Overview of series and parallel component configuration.
The other LED went out The other LED remained lite.
What happened when you removed an LED from each of these circuits?
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24. Circuit Configuration
Circuit Theory Laws
Circuit Configuration
Digital Electronics TM
1.2 Introduction to Analog
Components in a circuit can be connected in one of two ways.
Series Circuits
Components are connected end-to-end.
There is only a single path for current to flow.
Parallel Circuits
Both ends of the components are connected together.
There are multiple paths for current to flow.
Overview of series and parallel component configuration.
Components
(i.e., resistors, batteries, capacitors, etc.)
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25. Kirchoff’s Voltage Law (KVL)
Circuit Theory Laws
Kirchoff’s Voltage Law (KVL)
Digital Electronics TM
1.2 Introduction to Analog
In this circuit we used a 5V power source.
The resistor you measured had roughly 3V across it.
What did you guess would be the voltage across the LED?
VTotal=VR1 + VLED
5V = 3V + 2V
Overview of series and parallel component configuration.
Power Source (a)Voltage across LED and Resistor (b) Voltage across Resistor only
5V V V
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26. Series Circuits Characteristics of a series circuit
Circuit Theory Laws
Series Circuits
Digital Electronics TM
1.2 Introduction to Analog
Characteristics of a series circuit
The current flowing through every series component is equal.
The total resistance (RT) is equal to the sum of all of the resistances (i.e., R1 + R2 + R3).
The sum of all of the voltage drops (VR1 + VR2 + VR2) is equal to the total applied voltage (VT). This is called Kirchhoff’s Voltage Law.
VR1 IT + -
Characteristics of a series circuit. + + VT
VR2 - - - + RT
VR3
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Copyright 2009

27. Example: Series Circuit
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Example:
For the series circuit shown, use the laws of circuit theory to calculate the following:
The total resistance (RT)
The current flowing through each component (IT, IR1, IR2, and IR3)
The voltage across each component (VT, VR1, VR2, and VR3)
Use the results to verify Kirchhoff’s Voltage Law. VT + -
VR2
VR1
VR3 RT IT
IR1
IR3
IR2
Pause the presentation and allow the student to work on the example. The solution is on the next three slides.
Project Lead The Way, Inc.
Copyright 2009

28. Example: Series Circuit
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Solution:
Total Resistance:
Current Through Each Component:
This slide provides the solution. If you print handouts, don’t print this page. (1 of 3) V I R
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Copyright 2009

29. Example: Series Circuit
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Solution:
Voltage Across Each Component: V I R
This slide provides the solution. If you print handouts, don’t print this page. (2 of 3)
Project Lead The Way, Inc.
Copyright 2009

30. Example: Series Circuit
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Solution:
Verify Kirchhoff’s Voltage Law:
This slide provides the solution. If you print handouts, don’t print this page. (3 of 3)
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Copyright 2009

31. Kirchoff’s Current Law (KCL)
Circuit Theory Laws
Kirchoff’s Current Law (KCL)
Digital Electronics TM
1.2 Introduction to Analog
Note:
LEDs can be viewed as resistors in this circuit to simplify the discussion.
The 330Ω resistor was also removed to make the relationship easier to see.
Why do you think the 330Ω resistor placed in the actual circuit when the components are arranged this way?
For components that are in series, the current is the same in each component regardless of the resistance values.
In this circuit configuration, if R1 and R2 have different resistances the current is not the same.
What would R1 and R2 have in common?
Overview of series and parallel component configuration.
Voltage
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Copyright 2009

32. Parallel Circuits Characteristics of a Parallel Circuit
Circuit Theory Laws
Parallel Circuits
Digital Electronics TM
1.2 Introduction to Analog
Characteristics of a Parallel Circuit
The voltage across every parallel component is equal.
The total resistance (RT) is equal to the reciprocal of the sum of the reciprocal:
The sum of all of the currents in each branch (IR1 + IR2 + IR3) is equal to the total current (IT). This is called Kirchhoff’s Current Law. + -
VR1
VR2
VR3 RT VT IT
Characteristics of a parallel circuit.
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Copyright 2009

33. Example: Parallel Circuit
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Example:
For the parallel circuit shown, use the laws of circuit theory to calculate the following:
The total resistance (RT)
The voltage across each component (VT, VR1, VR2, and VR3)
The current flowing through each component (IT, IR1, IR2, and IR3)
Use the results to verify Kirchhoff’s Current Law. 33 + -
VR1
VR2
VR3 RT VT IT
IR1
IR2
IR3
Pause the presentation and allow the student to work on the example. The solution is on the next three slides.
Project Lead The Way, Inc.
Copyright 2009

34. Example: Parallel Circuit
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Solution:
Total Resistance:
This slide provides the solution. If you print handouts, don’t print this page. (1 of 3)
Voltage Across Each Component:
Project Lead The Way, Inc.
Copyright 2009

35. Example: Parallel Circuit
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Solution:
Current Through Each Component: V I R
This slide provides the solution. If you print handouts, don’t print this page. (2 of 3)
Project Lead The Way, Inc.
Copyright 2009

36. Example: Parallel Circuit
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Solution:
Verify Kirchhoff’s Current Law:
This slide provides the solution. If you print handouts, don’t print this page. (3 of 3)
Project Lead The Way, Inc.
Copyright 2009

37. Summary of Kirchhoff’s Laws
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Gustav Kirchhoff
German Physicist
Kirchhoff’s Voltage Law (KVL):
The sum of all of the voltage drops in a series circuit equals the total applied voltage.
Kirchhoff’s Current Law (KCL):
The total current in a parallel circuit equals the sum of the individual branch currents.
Summary of Kirchhoff’s Laws.
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Copyright 2009

38. Up Next
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
Now that you have been introduced to some of the basic characteristics, components, and measurement tools used in electronics, we will build on that knowledge in the upcoming activities.
Scientific & Engineering Notation
Component Identification: Analog Devices
Circuit Theory Laws
Hand Calculations
Simulation
Breadboarding
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39. Analog Versus Digital
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
The circuits we have explored to this point have included only analog components.
Later we will be learning what some of the digital components are and how they can be used to create desired outputs to a circuit given specific inputs.
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Copyright 2009

40. The Random Number Generator
Circuit Theory Laws
Digital Electronics TM
1.2 Introduction to Analog
The Random Number Generator (RNG) is an example circuit that we will use to illustrate all the parts of a complete circuit design.
It includes an analog section and two digital sections.
Push Button
Push
Button
Imput
Analog
Section
Sequential
Logic
(Digital)
Combinational
Random
Number
Output 1 2 3 4 5 6
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Copyright 2009