Electronics - Chp 13

Electrical conductor

materials that allow an electric current to pass through easily

Electrical insulators

materials that do not allow electricity to flow through them, they have high resistance

Semi-conductors

materials have resistance to electrical current between that of a conductor and insulator, can be used to control the flow of electricity; such as switching it on and off, or routing it in another direction

System

a combination of parts or components, working together to achieve a particular outcome, requires an input, process, and output

Input

causes the system to do something

Process

accepts the input and does something with it

Output

the result of the process

Electronic circuit

a system of electronic components that are connected together to perform a particular function

Switch

breaks or completes the circuit, stopping or allowing the flow of current, and changes the direction of motors

SPST switch

• single pole, one switch can control a single circuit at a time

• single throw, refers to the one output that can be powered

• used to turn the circuit on and off

SPDT switch

• single pole, one switch can control a single circuit at a time

• double throw, refers to the two outputs that can be powered by one switch

DPST switch

• double pole, one switch can control 2 circuits

• single throw, refers to one output

DPDT switch

• double pole, one switch can control 2 circuits

• double throw, refers to the two outputs that can be powered by one switch

• changes direction of the motor

DIP switch

• row of on/off switches

Electromagnet

• made up of a copper coil wrapped around an iron bar

• when the circuit is powered, the electromagnet is magnetised

Solenoid + Use

• converts electric current into linear movement

• a current passes through a coil of wire around an iron core

• the iron core is magnetised and a metal bar is pulled into the centre of the coil

- solenoids are used to operate switches, or electronically lock doors

Relay + Use

• electromagnet is magnetised and attracts the armature, which forces the switch contacts together

- used to safely turn on and off circuits that require very high electrical currents, opening and closing of security gates, raising and lowering high window blinds

Electromagnet - a contact

• normally open, off by default

• when the coil is magnetised, it closes and conducts current

Electromagnet - b contact

• normally closed, on by default

• when the coil is magnetised, it opens and does not conduct current

Electromagnet - c contact

• a common switch is when a switch is connected to a NO (normally open) terminal and NC (normally closes) terminal, and it switches between the two when the coil is magnetised

Wire

used to connect the separate components in a circuit, connections between wires are made by soldering

Diode

• semiconductor components which allow current to flow in one direction only

• polarised component

Polarised component

• it matters which way you connect them in a circuit, as they have an anode and a cathode

• they are forward biased and will only conduct electricity when the anode is connected to the positive terminal, and the cathode is connected to the negative terminal

• they are reverse biased and will not conduct electricity if connected the wrong way around

LED

• light emitting diode, similar to diode but has a bulb in the middle which lights up when a current is passed through

• the longer leg is the anode and the shorter leg is the cathode

• the shorter cathode is next to the flat side of the LED

• 7 segment LED, is commonly used to form any number from 0-9

Capacitor

• used to store electricity and then release it quickly

• two pieces of metal are separated by an insulator

• voltage is applied, and electrical charge is forced onto one plate and taken from the other

• when the capacitor is fully charged it has the same voltage as the battery charging it

Capacitance

the measure of how much charge the capacitor can hold

What is capacitance measured in + with?

• farads

• multimeter

Capacitor Use

• holds onto charge when the battery is disconnected, can be used in timing circuits

Types of capacitors + Functions

Fixed/non-electolytic/non-polarised capacitor

• can be connected in any way in the circuit, usually very small

Electrolytic/polarised capacitor

• forward biased, must be wired correctly

• hold more cahrge thatn non-electrolytic capacitor, often used with resistors to create a time delay

Variable capacitor

• capacitance can vary, usually by twisting a knob or screw, useful in adjustable timer devices

Capacitor circuit example:

• switch is closed (position a), capacitor charges up until it reaches full capacitance

• switch is opened (position b), resistor determines how quickly the capacitor discharges

Resistors

• control the direction of current, divide, voltages, adjust signal levels, and slow down the current in a circuit

How to read the resistance on a resistor?

• first band gives first digit

• second band gives second digit

• third band gives number of 0s

• fourth band gives the tolerance

  • red is 2%

  • gold is 5%

  • silver is 10%

  • none is usually 20%

Resistor above

1000 × 0.05 = 50

Tolerance is between 1050-950 Ohms

What is the difference between a linear + non-linear resistor?

• a linear resistance provides the same resistance once set

• a non-linear resistor changes its resistance, eg changing it based on environmental factors; thermistor, light dependent resistor

Fixed resistor

resistance is set and cannot be changed

What is the difference between a variable resistor and a pentiometer?

• physically the same, difference depending on how they are wired in the circuit

• resistance can be adjusted by a knob, or using a screwdriver

• when wired to centre terminal and one of the outer terminals, used as a variable resistor

• when wired to all three terminals, centre takes in voltage

Variable resistors: Use

• sets the sensitivity of the circuit

• dimming switches

How does the resistance of an LDR change in different light levels?

• light levels high → resistance low

• light levels low → resistance high

Transistor

• very sensitive electronic switches

• they have three legs; emitter, base and collector

• function as a high speed, automatic switch in a circuit or as an amplifier of current

Design a circuit which turns on a light when light levels are low

Design a circuit which turns on a light when light levels are high