Systems - EdexcelElectrical components

There are a huge number of electrical components available to buy from specialist suppliers. Items such as bulbs, buzzers and sensors are all readily available, and prices decrease as more units of the product are bought. Items can be matched to ensure they are the right voltage and current rating for the product being produced.

Resistors limit the flow of current around a circuit and can prevent damage to components.

Resistors used in electrical circuits have a tolerance of how much power they allow into a circuit - the smaller that tolerance is, the less likely the circuit will be overloaded and damaged, but the more expensive the resistor will be.

When reading the value of a resistor, it must be held with the gold or silver band to the right - this is the tolerance band.

Rather than have resistors available for every number possible, resistors are only available in what is called a ‘preferred value’. These values are indicated by the number created by the first two coloured bars on the resistor.

Example

The above picture shows yellow (4), violet (7) and red (× 100)

= 47 × 100

= 47,000 ohms (Ω)

Resistors are available in series - the series refers to the resistors tolerance. The most common two are called E12 and E24. The E12 and E24 series include resistors with the following preferred values:

Zeros from the third band (the multiplier) can be added behind these numbers, eg 100 becomes 1,000 (× 10), 330 becomes 33,000 (× 100), etc.

The amount of tolerance a resistor has is shown with the colour of the fourth stripe down and is usually silver or gold. The E12 series resistors have a silver fourth band and the E24 series resistors have a gold fourth band.

E12 resistors have a tolerance of 10 per cent, meaning that the value of the resistor could be smaller or larger by 10 per cent, eg a 300 Ω E12 resistor could range from 270 Ω to 330 Ω.

E24 resistors have a tolerance of 5 per cent, meaning that the value of the resistor could be smaller or larger by 5 per cent, eg a 300 Ω E24 resistor could range from 285 Ω to 315 Ω.

Circuit boards

Circuit boards are used in most electronic systems as they ensure reliable connections between components. Components must be connected accurately for the circuit to work properly, and different types of circuit boards are available for different tasks. Circuit boards can be designed by using a computer aided design (CAD) program to create a circuit that can be input into a CNC router and accurately etched into the surface.

Stripboard is a copper board and is often used for prototyping as it is the simplest type of board to create circuits on without the use of expensive machinery. Stripboard circuits are not printed as they have pre-laid tracks on which to lay the circuit.

While stripboard is made of copper, it is different to copper-clad board, which is used particularly for small, simple electronic circuits. It is a type of printed circuit board where the connections are either cut in with a computer numerical controlled (CNC) router or etched onto the surface using a photoresist pen. This is then placed in an etching bath, leaving the pen-drawn areas in place. This is a cheap way of creating a circuit without the use of expensive materials, although it isn’t very accurate and can be time-consuming.

Photoresist, printed circuit board (PCB) prints a photosensitive layer above the copper from a computer aided design (CAD), which is then exposed to ultraviolet light. Developer solution is then used to rinse away the exposed parts, leaving only the circuit ready for use. This is an accurate way to create complex and easy-to-use circuit boards with only the copper areas, where the components will be attached, left exposed.

These circuit boards are made from glass-reinforced plastic (GRP); this material is light in weight and strong. GRP is an insulator to electricity and resists corrosion well. One side of the circuit board is often printed with labels, so that each component can be placed in the correct place. PCBs can be produced in large numbers, quickly and accurately, but the machinery to produce them is expensive, so it can be more cost-effective to buy them in from a specialist factory.