Electronics

Chapter 12

Objectives

      Identify the value of resistors based on the resistor color code State the purpose of using capacitors in conjunction with resistors for timing functions Recognize purpose of common electronic components (resistor, capacitor, diode) Explain purpose of specific ICs Convert schematics into electronic circuits Construct and troubleshoot electronic circuits

Electronics: definitions

    Electronics: science that deals with electron flow Becomes a technology when applied to serve a useful purpose (camera, stereo, computer, etc) Electronic Circuit: a group of electronic components designed to perform a certain, specific, function.

 standard components are used in different ways Electronic Device: made of one or more electronic circuits

Resistors

 Resistors: restrict the flow of electrons  To protect components from burning out   To modify recharging times for batteries and capacitors Ohm: unit of measurement for resistance  Amount of resistance in a resistor is determined by reading the colored bands on the resistor

Reading a resistor

   Four-band resistor    First TWO bands - represent digits Third band - represents the multiplier Fourth band – represents the resistance tolerance Five band resistor:    First THREE bands - represent digits Fourth band - represents the multiplier Fifth band – represents the resistance tolerance

Note: any resistor with no tolerance band has a tolerance of +/- 20%

Resistor Color Band Chart

Troubleshooting Resistors

    Calculate the value of the resistor using the bands Measure resistance using a multi-meter If it is not within the tolerance the resistor has failed (BE SURE THERE IS NO POWER FIRST!!!)



Variable Resistors

Amount or resistance is adjustable  Dimmer switches on lights at home   Volume controls on stereos How they work    Inside is a length of resistance material (often carbon) The wiper slides along the resistance wire when knob is turned The greater distance that the electrons flow through the resistance material the more restricted the flow

Capacitors

  Ability to store (and discharge) electrical charge very quickly  Used to smooth out variations in power pulses  Ie: AC units, TV’s , camera flashes, etc Farad (F): unit for measuring capacity  Most capacitors are rated in microfarads (millionths) or picofarads (trillionths)  Most capacitors rate only a few microfarads

Capacitor types

  Ceramic Disk: made of ceramic and silver Electrolitic: made of an electrolyte and aluminum

Diodes

 Allows for only one way flow of electricity  (similar to a check valve in a fluid system)   Can also serve as a switch only allowing the flow of electricity when it reaches a certain voltage.

Size usually indicates the amperage rating

Diodes

 Electricity can only flow:   INTO the diode through the cathode OUT OF the diode through the Anode  This is called Forward Bias  Alternating current reverses polarity all the time ….. The diode only allows it to flow in one direction.

 Testing diodes with multi-meter:  A good Diode shows LOW resistance (ohms) in one direction and infinitely high in the opposite direction

Rectifier Circuits

  Convert AC current to DC current: since electricity only flows in one direction through diode and it is restricted in the opposite direction.

The result is a pulsating DC current  (the gap between pulses is the half of the AC cycle that is blocked)

Rectifier Circuit

Zener Diodes

    Only allows one way flow of electricity (just like a standard diode) Difference is that it conducts electricity in the Reverse Biased direction It is able to maintain a steady voltage Often used in voltage regulation circuits

Light-Emitting Diodes (LEDs)

    Can be produced in many colors Cathode (attached to negative side of circuit) is shorter and indicated by a flat spot on the base of the LED Many uses: Flashlights, headlights, LED displays on digital readouts, etc.

Do not produce heat (wasted energy) so they are more efficient than incandescent bulbs

Transistors

 A solid-state switching device (no moving parts)  Bipolar Transistors: three connectors (emitter, base and collector   Current flows between the emitter and collector Current is “switched” on or off by applying current to the base.

 Can also be used for amplification Small current applied to B controls larger flow through E/C

Bipolar Transistors

Field Effect Transistors

    Similar to Bipolar transistors but…..

Cheaper to make Can carry more voltage than Bipolar Two types:  MOSFET: metal-oxide semiconductor field effect transistor (may have 4 th terminal)  JFET: Junction field effect transmitter (three terminals

Field Effect Transmitters

Integrated Circuits

 A collection of electronic circuits (indistinguishable to the naked eye) etched into a thin layer of silicon and installed into a plastic or ceramic housing  Housing contains series of pins that allow the IC to be installed into a base called a “socket”

Integrated Circuits

 Used for:   Counting functions Timing functions   Logic Functions (and, or, not) Two types (TTL & CMOS)

Integrated Circuit



CMOS –

Complimentary Metal Oxide Semiconductor  Works with up to 18V    Easily damaged by static electricity (con) Very little current draw (pro) Identified by numbers starting with “4”  TTL – Transistor transistor logic –     works on low voltage (5V or less) Not damaged by static electricity (pro) Has a high current draw (con) Identified by numbers starting with “74”

Uses for ICs

    7448-Decoder drivers for 7 pin leds  Digital readouts on clocks, watches, etc 741-operational amplifier (op-amp)- increase AC or DC signal by up to 100,000 times  Radios, TV, or any sound outputting device 555 (CMOS technology)   Monostable applications – turns on for a given time (seatbelt light on your dashboard) Astable applications – blinking lights (indicators) 556 – two 555 combined can do both functions  Blinks for a fixed period of time then turns off

Fuses and Circuits

     Protect electronic circuits form excessive current flow (amps) Both open circuit in case of excessive loads Breakers can be reset Fuses melt and must be replaced Must be sized properly to protect components

Circuit Boards and Solderless Breadboards

   Platform for electronic circuits Copper paths make the connections between components Solderless breadboards do the same and components can be easily installed or removed

Schematic Diagrams Symbols