Class 2 Basic Electronics

7/27/2019 Class 2 Basic Electronics

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Whats Included Whats an Electrical Circuit?

Invisible Quantities (V, I, R)

Safety

Basic Components

Resistors, Batteries, Light Emitting Diodes(LEDs), ICs, Voltage Regulator

Ohms & Kirchhoffs Laws

Simple Circuits

Integrating to the Parallel Port (basics only)

Textbook & Web References


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Whats an Electrical Circuit?

Every circuit requires these three things:

Power Source

Load

Conductor

Optionally, a circuit may include a control device such

as a switch

9V


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Three Main Invisible Quantities

Voltage, symbol - V, units - Volts

Provides the push

Current, symbol - I, units - Amperes (Amps)

Flow of Electrons

Amount of Current is dependent on Voltage and

Resistance

Resistance, symbol - R, units - Ohms (S) Limits the amount of current

Represents the load of the circuit


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Safe Levels

Voltage: 30 V

Voltages inside a computer do not exceed 12 V,

except at the power supply and power switch,

which could be at 120 V, depending on computerstyle. Be careful in these areas!

Current: 5 mA (0.005 Amperes)


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Voltage Can Be Provided From

A battery


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Voltage Can Be Provided From

Breadboard (trainer)


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Current

is simply the flow of electrons

Direction depends on convention

Conventional Current Flow (+) to (-)

Electron Current Flow (-) to (+)Electron flow isfrom (-) to (+) (flow ofelectrons)

Conventional flow

is from (+) to (-) (holeflow)


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Resistors Basic Specs

Can be rated by

Resistance (Ohms, S)

Tolerance (% of nominal value)

Power Rating (Watts)

Schematic Symbol


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Resistors Types

Fixed

Variable (Potentiometer, Rheostat)


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Resistors Colour Code


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Resistors Colour Code Example

1st band: orange = 3

2nd band: orange = 3

3rd band: red = 2 (i.e. 102)

4th band: gold = 5%

33 x 102

= 3300 S

= 3.3 kS


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Resistors 5 Band Colour Code


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Resistors Typical Power Ratings


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Ohms Law

R

VI

Current (I) is proportional to Voltage (V)and inversely proportional to Resistance (R)

RIV I

VR


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Ohms Law and Power Formulas


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Kirchhoffs Voltage Law (2)

5 V

3 V

2 V

D0

GND

Parallel Port


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Kirchhoffs Current Law

The current entering a junction must equalthe current leaving the junction

Use in parallel circuits.

4 A1 A 3 A


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Series Circuits

One current path, therefore the current is

the same everywhere

...21 RRRT

Total resistance is the sum of theindividual resistances


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Parallel Circuits (2)

)(

)2(

...111

1

21

21

321

valuesametheif

n

R

onlyif

RR

RRRRR

RT


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Light Emitting Diodes

A type of diode designed toemit light Can be visible or

IR

2 V voltage drop

Typically draws 20 mA (0.020

A)

Schematic Symbol


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A Simple LED Circuit


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Interfacing LEDs to the Parallel Port

D0

D6

D5

D4

D3

D2

D1

D7


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Protecting the Parallel Port

Use a 74LS245 Octal Bus Transceiver toprotect the computer parallel port


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Interfacing a Motor to the Parallel Port

2N3904

TIP31

(A stepper motor would require

more outputs)

D0

M

9V

E

BC


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Integrated Circuits

7400 series typically used for logic gate

experiments

Very susceptible to

voltage variations and

static discharge

Note pin 1 on diagram

Refer to applicable data-

sheet for pinouts

1

7 8

14


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7805 Voltage Regulator

Part of the 78xx series of voltage regulatorsCan be used to convert 9 V to 5 V for digital

circuits

7812 Regulated Power supply design


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7812 Regulated Power supply design

Class 2 Basic Electronics

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