Electronic and mechanical systems

Inputs, outputs and processes in systems used by designers

Selecting components

Since electronics and mechanical systems were first developed, the speed at which new materials, techniques and processes have been developed has been rapid and revolutionary. Scientists, designers and engineers have worked to invent and improve systems that impact lives.

When designing a system, electronic or mechanical, it is important to know what a product is capable of doing - this would be the ‘output’.

Systems are often designed using a system block diagram that considers the ‘input, process and output’ of a system. How the system will work is the ‘process’ and the ‘input’ is the part of the system that enables the process to start happening.

A simple block diagram representation moving through an input, process and output.

Selecting components to use in the production of electronic and mechanical products is complex, and these should be carefully chosen to ensure a product is functional. There are a range of different sensors, control devices and output devices that can be used together or separately depending on what function the product needs to achieve. These components are split into the three categories: inputs, processes and outputs.

Input

SensorFunctionUse
Light dependent resistor (LDR)The resistance changes as the light level changes, and the change in resistance can be used as an inputSolar garden lights and street lighting
ThermistorThe resistance changes as the temperature changes, and the change in resistance can be used as an inputFridges, central heating systems and freezers to maintain temperatures
Piezoelectric sensorCan change mechanical motion or force into electrical energy - it can produce an electrical pulse from pressure, such as by hitting itIgniting lighters and in microphones (where soundwaves create pressure that makes the electrical pulse)

Process

Control deviceFunctionUsed
SwitchA switch can either allow or prevent electrical power from flowing round a circuitAny device that needs power to be turned on and off
ResistorTo limit the flow of current - they are made to restrict current flow in varying degrees (resistance)All electrical products - it helps control the flow of current and protects delicate components from being overloaded
Programmable componentsA programmable component is a chip that can be programmed to make decisions based on an inputMost modern electrical products - washing machines are programmed to work when the drum door is shut and the on/off button is pressed

Output

Output deviceFunctionUse
LoudspeakerUses pulses of electricity to move an electromagnet that vibrates to create soundSpeakers, headphones and radios
MotorConverts power into rotary motion that can turn a spindle linked to gears or wheels to make them moveCars and trains
Light-emitting diode (LED)A long-lasting, low-power lightTorches, lamps and power indicators

How an electrical or mechanical product looks is important when trying to design a product that appeals to the target market. Components need to be housed in a protective, practical, safe and aesthetically pleasing coating to be both usable and appealing.

For example, products made of lightweight aluminium, such as mobile phones, can be anodised, which bonds an insulating, coloured and protective layer. This improves the aesthetics and the functionality of a metal product by giving a metallic-look covering of any colour, protecting the metal casing from scratches, wear and corrosion.

Fashion and trends have a big influence on the amount of electrical and mechanical products sold. As products with new features are developed, people want the latest models. This can increase the amount of waste that needs to be disposed of safely. The disposal of electrical products is damaging to the environment. Some metal parts can be recycled safely and reused, but other components, such as batteries, are difficult dispose of safely.

Protective insulators, eg plastic, are often used to protect the user from the flow of electricity and prevent the risk of electrocution in larger products such as TVs or fridges. Plastic casings for products can be made by vacuum forming around the inner product to ensure it is covered, protected and aesthetically pleasing.

The cost and availability of many components varies massively; the cost per single unit is always considerably higher than if bought in bulk. Components are often made in large factories abroad, making shipping of small numbers of components both expensive and slow. As such, most electronic components are mass produced and packaged in large quantities.

Producing electronic and mechanical components can require specialised equipment, making parts expensive to produce. The cost of a component is also high when being sold as a single item to the consumer because a large box of components has to be opened and could remain ‘in stock’ for some time before all of the components in the box are sold.

Example

Below is a costing table for packs of resistors:

QuantityCost
10£1.00
20£1.40
100£3.00

It is possible, from the above table, to calculate the cheapest option if 40 resistors are required.

If buying in packs of 10, four packs are required.

40 ÷ 10 = 4

4 × 100 = £4.00

If buying in packs of 20, two packs are required.

40 ÷ 20 = 2

2 × 140 = £2.80

Although the pack of 100 appears to be the cheapest cost per unit, the pack has a set price of £3.00.

Therefore, the cheapest option is two packs of 20 resistors.

Question

Below is a costing table for packs of buzzers:

QuantityCost
10£6.00
100£55.00

What is the price difference when purchasing one buzzer from either pack?

600 ÷ 10 = 60

= 60p each

5,500 ÷ 100 = 55

= 55p each

Price difference = 60 - 55

= 5p