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Output devices allow a system to present information back into the ‘real’ world. They take the signal from the process device of a system and turn it back into physical or ‘real world’ signal, such as light or sound. Examples can be seen everywhere, from car indicators to doorbell buzzers or information displays.

Light outputs

Light can be produced in different ways; a light-emitting diode (LED) is the most common component used for producing light. LEDs are made from two types of semi-conductor material that emit light when current flows through it:

• LEDs only work in one direction
• the long leg is the positive (+) side known as the anode and the short leg is the negative (-) side known as the cathode

Advantages

• LEDs come in a wide range of colours and sizes
• they are more energy efficient then other bulbs and have a longer life span

Disadvantage

• a resistor is placed in series with a LED to protect the LED from a high supply voltage - if the wrong value resistor is used, the LED may burn out or not light up at all
• the light from an LED is not always visible at certain angles

Sound outputs

Sound can be produced using buzzers.

Buzzers

• buzzers have an oscillator inside a plastic case
• when current flows through them they produce a buzzing sound, often around 400 Hertz (Hz) in frequency depending on the type of buzzer used
• examples of their use include in doorbells and alarms