Electric and Electronic Circuits 3º ESO

Review and Extension

Atomic structure● Atoms contain positively charged

particles (protons), negatively charged

particles (electrons), and particles with no

charge (neutrons)

● Protons and neutrons are found in the

nucleus of the atom, while electrons orbit

around the nucleus on different “paths”

called orbital shells

● Like charges repel, and opposite charges

attract. We call the energy generated by

these forces electricity

Electricity● Electricity is a form of energy that

lets electrons move from one atom

to another

● Electrons are attracted to the

positive charge of protons in the

nucleus, but in some materials the

outermost electrons (valence

electrons) are able to leave the atom

● Electric current is the flow of

electrons through a conductive

material

Conductors, insulators and semiconductors● Conductors are materials in which

valence electrons are able to move

freely between atoms under the

influence of an electric field

● In insulators, it is more difficult for

valence electrons to move between

atoms

● Semiconductors have an electrical

conductivity that is intermediate

between that of a conductor and

that of an insulator

Electronics● Electronics is the control of the

movement of electrons in

semi-conducting materials (such as

silicon and germanium)

● Normally, semiconductors act as

insulators, but they can become

conductors due to changes in certain

factors (electric fields, magnetic

fields, pressure, etc.)

Analogue vs. Digital Electronics● Analogue electronics

studies systems where the

variables can take on any

values over time

● Digital electronics studies

systems where the

information is encoded in

discrete values

● The voltage range in a

digital system is called the

logic level

Direct Current● Direct current is the current

produced when electrons

always move in the same

direction an electric circuit

● The voltage and current of a

direct current circuit are small

● Cells and batteries supply

direct current

● Usually used in portable

devices

Alternating Current● Alternating current is the

current whose value whose

value and direction vary

cyclically in a circuit

● Voltage and current are

higher than in a DC circuit

● Voltage and current can be

increased or decreased using

transformers

● Generated in power plants to

be delivered to households

and other consumers

Current● Current is the variable that

tells us how many electrons

flow through the cross-section

of a conductor per unit of time

● Its unit in the international

system is the ampere (A)

● True direction - negative to

positive

● Conventional direction -

positive to negative

Voltage● Voltage is the variable that tells us

the difference in electrical energy

per unit of charge between two

points in a circuit

● Unit is the volt (V)

Resistance● Resistance is the variable that

represents the opposition to the

flow of the electric circuit

● When wires are thinner and longer,

it is harder for the electrons to pass

through

● Unit is the ohm (Ω)

Reading Resistors● The most common resistors are

made from carbon and coated

with a ceramic material

● We can find out the value of a

resistor by the colored rings on it

Electrical Energy● Electrical energy is the energy

generated by the forces of

attraction and repulsion between

charged particles

● Most common units are the joule

and the kilowatt-hour (kWh)

Electrical Power● Electrical power measures the

energy that is consumed by a

load device or delivered by a

power source over a certain

period

● Power is the amount of energy

per unit of time

● P = E/t = V x I

Joule Effect● As electrons move across

electrical conductors, some of

their kinetic energy is

transformed into heat due to

friction

● Heat lost by the Joule effect (Q)

is calculated by this equation:

Q=I^2 x R x t

Capacitors● A capacitor is a component used

to store and discharge electrical

energy

● The capacitance of a capacitor is

the amount of charge that it can

store for a certain voltage

● Capacitance is measured in

farads (F), but the most common

units for circuits are micofarads,

nanofarads, and picofarads

Relays

● A relay is a switch controlled by

an electromagnet

● It is used to open or close contact

● Relays exploit the relationship

between electric fields and

magnetic fields

Diodes● A diode is an electronic

component with two electrodes

called the anode (+) and the

cathode (-)

● These electrodes have the

characteristic of allowing the

current to flow in the

anode-cathode direction, but not

the reverse

● They can be used as control and

safety elements

LEDs● An LED (light-emitting diode) is a

diode that can emit light because

it is polarised directly

● In the opposite direction, it does

not let the current flow and acts

like an open switch

Transistors● A transistor is an electronic

component used to amplify

electrical signals or as a switch

● A transistor has three pins:

emitter (E), base (B), and

collector (C)

● There are two basic types of

transistors: NPN and PNP

Transistors● Transistors can function as

switches or amplifiers

● When functioning as a switch a

small current flowing through the

base will allow a larger current to

flow through the collector

● Transistors can also amplify

current flowing through the base

so that much more current flows

through the collector. β is the

gain of the transistor

Programming of electronic systems and Robotics 3º ESO

Review and Extension

Automechanisms and robots

● An automated mechanism is a device or

machine that performs a specific task and

whose operation cannot be changed

● A robot is a programmable automated

machine that captures information about

its surroundings, processes this

information and acts on it

Controller Boards● We use a computer (either external or

built-in) to control the processes that a

robot performs

● But a computer’s microprocessor cannot

communicate directly with sensors or give

commands to motors, lights, etc.; so we

need a controller board

● A controller board is an electronic circuit

that acts as an interface between the

computer and the devices that we want to

control by adapting the input and output

signals

Heat Sensor Light Sensor Motor

Controller Board

Computer

Microcontrollers● A microcontroller is a programmable

integrated circuit on a single chip that

covers all the basic functions of a

computer: processing unit, memory and

input and output peripherals

● Microcontrollers are cheaper and use less

power than a computer, but only perform

one specific function and have less

memory

● Microcontrollers can be directly connected

to sensors and motor

Control Systems● A control system regulates and

controls the operation of an

automated mechanism or process

so that it does what we want it to

do

● There are two types of control

systems: open loop and closed loop

● Open loop systems do not take into

account the output signal in the

control action

● For example, a fan does not change

its operation based on the room

temperature

Controller ActuatorInputSignal

OutputSignal

Open Loop System

Closed Loop Systems● In these systems, the output

signal is compared to the

input signal to correct errors

and adjust the control action

to the value we require

Controller ActuatorInputSignal

OutputSignal

Sensor

Comparator

● A heating thermostat uses a sensor

to compare the room temperature

to the programmed temperature

and decide whether to turn the

heat on or off

Controller Boards● Basic elements: microcontroller

and the input and output ports

● Connect sensors and actuators

through the analogue and

digital inputs and outputs

● Each contact can provide or

receive a maximum of 40 mA

● Must connect the board to a

computer via USB to upload

the programs, but after that it

can run on its own using an

external power source

Sensors● A sensor is a device that

detects physical or chemical

variables (temperature,

humidity, light intensity,

distance, acceleration, tilt,

pressure, strength, etc.) and

transforms them into electrical

variables

Actuators● An actuator is a device that

converts electrical energy into the

activation of a process in order to

act upon an automated process

● Arduino provides a max. Output of

40 mA, which is sufficient for an

LED and a servomotor, but not for

a Direct Current (DC) motor

LEDs● LEDs have polarity so we have to

connect the anode and cathode

correctly

● Need a resistor of approximately

220Ω connected in series to

withstand the current of an

Arduino board

DC Motors● DC Motors convert electrical energy into

mechanical energy to rotate a shaft

● Depending on the polarity, the shaft turns one

way or the other

● To power a DC motor with an Arduino board we

need to do one of the following:

○ Connect a shield (an extension board) for

DC motors

○ Use a transistor to amplify the signal to the

motor

○ Connect a relay to operate the motor

○ Connect motor to an integrated L293 or

L298 circuit

Servomotors● Servomotors, or servos, are

precision DC motors that have a

motor inside with a speed

reducer and a small control

circuit that only allows them to

rotate from 0 to 180°

● They have three wires: one is

connected to +5V, one is

connected to GND (ground), and

the last is connected to a digital

pin

Programming an Arduino Board● To program an Arduino board, we can

use the Arduino Integrated

Development Environment (IDE), an

application for editing and debugging

code that uses a special programming

language

● We can also use S4A (Scratch for

Arduino). The downside is that the

Arduino board must be connected to a

computer to run the program

● Finally, there is Ardublock, a visual

programming environment similar to

Scratch