Describe common output transducers (lamp, LED, buzzer, motor, loudspeaker) and the energy conversion each one performs

What this dot point is asking

SEAB wants you to describe the common output transducers - the lamp, LED, buzzer, loudspeaker and motor - and to state the energy conversion each performs. The central insight is that an output transducer (an actuator) does the reverse job of a sensor: it turns the circuit's electrical signal back into a form we can see, hear or use, such as light, sound or movement.

The answer

What an output transducer is

An output transducer converts electrical energy into another useful form of energy. It is the opposite of an input transducer: where a sensor turns light or heat into an electrical signal, an output transducer turns the electrical signal into light, sound, movement or heat. Output transducers are how a circuit affects the outside world.

The common output transducers

• A filament lamp converts electrical energy into light (and heat). It is bright but draws a fairly large current.
• A light-emitting diode (LED) converts electrical energy into light efficiently, with a small current, and needs a series resistor. It is the usual visual indicator.
• A buzzer converts electrical energy into sound, giving a simple tone for warnings and alarms.
• A loudspeaker converts electrical energy into sound, reproducing varying signals such as music and speech.
• A motor converts electrical energy into kinetic (movement) energy, used to turn wheels, open valves and drive fans.
• A relay uses electrical energy to move a magnetic contact, switching a separate, larger circuit (covered in its own dot point).

Matching the transducer to the job

Choose the output for what you need: an LED for a low-power visual indicator, a lamp for brighter light, a buzzer for a simple warning sound, a loudspeaker for reproducing complex sound, and a motor for movement. Each is rated for a certain voltage and current that the driving circuit must be able to supply.

Driving a high-current output

Many outputs (lamps, motors, buzzers) need more current than a logic gate or sensor stage can supply directly. The solution is to feed the small signal to a transistor through a base resistor, and let the transistor switch the larger current from the supply. For very large or mains loads, the transistor switches a relay whose contacts carry the heavy current.

Examples in context

Example 1. A reversing-camera beeper. When a car is put into reverse, a circuit drives a buzzer that beeps faster as an obstacle gets closer. The buzzer converts the electrical pulses into sound the driver hears. A transistor switches the buzzer current from the small control signal, a typical output-driving arrangement.

Example 2. An automatic fan. A thermistor circuit detects a high temperature and, through a transistor, switches on a motor that drives a cooling fan. The motor converts electrical energy into movement, turning the blades. Here the output transducer does physical work, showing that outputs are not only lights and sounds but actuators too.

Try this

• Cue. State the energy conversion performed by a loudspeaker. It converts electrical energy into sound energy.

• Cue. Name a suitable output transducer to produce movement and its energy conversion. A motor, which converts electrical energy into kinetic (movement) energy.

• Cue. Explain why a transistor is used between a logic output and a lamp. The logic output cannot supply the lamp current directly, so the transistor switches the larger current from the supply under the control of the small logic signal.