Output Devices & Actuators

An output device makes processed information available to a person or changes a physical condition.

Displays and projectors

An LCD controls light passing through liquid crystals to form an image. In an LED-backlit LCD, LEDs supply the backlight. A screen is useful for changing information viewed directly by its user.

An LCD projector shines light through liquid-crystal panels and lenses to project an enlarged image. A DLP projector uses many tiny tilting mirrors to direct light and form the projected image. A projector suits a class presentation; lighting conditions, distance and a suitable surface affect visibility.

Sound and movement

A speaker uses an electrical signal to move a cone and vibrate the air, producing sound. Stored digital audio is converted to an analogue signal by a DAC before suitable amplification/output.

An actuator changes a physical condition in response to a control signal. A motor can rotate a fan, a valve can release water, and a heater can raise temperature. A temperature sensor is not an actuator: it measures rather than heats.

Worked decision

A station needs visible departure information and announcements. A display shows changing text; speakers provide audible announcements. Neither alone meets both needs. A motor operating a barrier is another output, even though it does not show information.

Printer mechanisms are studied separately so each can be compared and practised.