Electronic systems and control 2012

ELECTRONIC SYSTEMS AND CONTROL

LIEZEL OOSTHUIZEN200932201

CURRENT

Current is the continuous movement of free electrons through the conductors of a circuit.

Ammeter - Measures the flow of electrons in a circuit, which is known as current - connected in series.

Symbol of current (I). The (I) unit of measurement

of electric current, the ampere, is named after André-Marie Ampère.

VOLTAGE+ The ability of a cell to

produce current is called voltage.

+ Voltage is the electricalpotential energy.

+ Is measured in Volts.+ Voltmeter Measures the voltage

produced by a power supply – always connected in parallel.

+ Symbol for Volt (V) or (E).

OHM’S LAW & RESISTANCE

Resistance - Free electrons move through conductors with some degree of friction.

Resistance is measured in Ohm (Ω).

Symbol of resistance (R).

A Resistor - Slows down the flow of electrons in a circuit.

EQUATIONS Resistance = voltage/current R= V/I Voltage = current x resistance V= I x R Current = voltage/resistance I=V/R

Resistance in Serie: When resistors are connected in Series, the effect is to add more

resistance to the circuit. E.g. The value of resistors in series: RT(Total) =

R1+R2+R3[Resistor Values] *A resistor is a series circuit is called a voltage divider.

Resistance in Parallel: When resistors are connected in parallel, the effect is to reduce the

resistance in the circuit. E.g. The value of resistors in parallel: 1/Rt = 1/R1 + 1/R2 + 1/R3

*Resistors in a parallel circuit is called a current divider.

CURRENT

VOLTAGE

RESISTANCE

V=

R=I=

Measuredin Volts (V).

Measured in Ohms(Ω).

Measured in Amps (A).

V

AΩ

I = V ÷ R

V = I x R

R = V ÷ I

RESISTOR COLOUR CODESThe First three bands give the value of the resistor in ohm(Ω).

The fourth band indicates how accurate the given value is.Resistor value: 2% - RED

5% - GOLD 10% - SILVER

E.g.:

RESISTIVE COMPONENTS

Variable Resistor Can be used to adjust

the flow of current in a circuit.

Thermistor Is a component whose

resistance varies with temperature.

Light Dependent resistor (LDR)

It’s a component whose resistance depends upon the amount of light falling on it – it reacts to light.

When the LDR in the circuit is covered up, the bulb gets dimmer and finally goes out.

CONTROL ELECTRICS

The switch It’s the simplest

control unit form in an electrical circuit. The simplest type of switch is the single pole single throw switch (SPST).

It has 2 parts: a pole & a contact.

Single pole double throw switch (SPDT).

Double Pole single throw switch (DPST).

Double pole single throw switch(DPDT).

Push to Make & Push to break switches:

MORE COMMON TYPE OF SWITCHES:

Toggle switch Push Switch

Slide switch Reed Switch

A Rotary Switch

RELAYS The Relay - is a switch turned on and off by an

electromagnet.

Relay Latch - Fixes a circuit in “On” position. - A latch is like a lock.

Relay Buzzer -The relay switches “on” and “off” very rapidly, producing a buzzing sound.

-A relay can therefore be used to make a crude buzzer.

CONTROL ELECTRONICS

THE DIODELIGHT EMITTING DIODES (LED)

Is a semiconductor device. It’s a component which allows

current to flow in one direction only. A Semiconductor diode consists of

a PN junction and has two terminals: [P] - Anode(+) [N] – Cathode(-) Current flows from the anode to the

cathode within the diode. When a forward voltage is applied,

the diode conducts. When a reverse voltage is applied,

their is no conduction.

A LED is a special form of diode that gives out light when connected the correct way around.

LED’s normally need to be connected in series with a resistor to prevent them drawing too much current and burning out.

LED’s are used mainly as visual indicators that a circuit is working or an appliance is “On”.

An LED converts electrical energy to light.

TRANSISTORS

A Transistor is a semiconductor device. Made of three layers of N-Type & P-Type semiconductor material, Geranium

and Silicone. The three layers are called - Emitter, Base & Collector.

There are three types of transistors:

NPN PNP

The NPN Transistor has a small current flowing to the base of the

transistor enables a large current to flow between the collector and emitter. The PNP Transistor uses a small base current and negative base voltage

to control a much larger emitter-collector current. The FET transistor – Field Effect Transistor only needs a small field of

current.

TIMING CIRCUITS CAPACITORS - A CAPACITOR IS A COMPONENT WHICH CAN STORE AND RELEASE ELECTRICAL ENERGY.

- CAPACITANCE IS MEASURED IN FARAD.

1. POLARIZED - CAPACITOR 2. NON – POLARIZED CAPACITOR

Polarized capacitors tend to be higher value types.

These have a positive(+) and negative(-) lead which must be connected the correct way round in a circuit (+ to + and - to -) .

Non-polarized capacitors which are low value types.

These can be connected either way round in a circuit.

Do not have a (+) or (-) lead.

Normally used to smooth a current in a circuit.

THREE FACTORS THAT INFLUENCE THE CAPACITY OF A CAPACITOR:

1.) Lowering the surface area of plates.

2.) Increase distance between plates.

3.)The kind of material used for dielectric.

REFERENCES:

Download.pptx. (n.d.). Retrieved from http://www.tes.co.uk/Download.aspx?storycode=6071059&type=X&id=6269844

explaining how Resistors work.ppt. (n.d.). Retrieved from http://teachersunderground.co.uk/Electronics/explaining%20how%20Resistors%20work.ppt

Garratt,J. (1996). Design and Technology. Cape Town: Cambridge University Press.

Ohm’s Law - Resources - TES. (n.d.). Retrieved April 30, 2012, from http://www.tes.co.uk/teaching-resource/Ohm-s-Law-6071059/addtofavourite/addtofavourite/

Resistor colour code wheel.ppt. (n.d.). Retrieved from http://teachersunderground.co.uk/Electronics/Resistor%20colour%20code%20wheel.ppt