Output Devices

Definition and Categories of Output Devices

  • Define Output Devices as a component of a control system that transfers information from the system to the outside world.
  • Know the classification of output devices into two categories: human perceptible outputs and machine driven outputs.
  • Appreciate that human perceptible outputs include lights, displays, sounds, while machine driven outputs include motors and relays.

Light Emitting Diodes (LEDs)

  • Recognise the importance of LEDs as output devices that provide simple, effective visual feedback.
  • Understand that LEDs emit light when an electric current passes through them.
  • Highlight the polarity of LEDs with the anode (positive) and cathode (negative); incorrect installation can prevent the LED from lighting up or potentially damage it.
  • Acknowledge the need for resistors to prevent LEDs from drawing too much current and burning out.

Liquid Crystal Displays (LCDs)

  • Comprehend the use of LCDs for more sophisticated visual display of information, such as numeric data or text.
  • Know the mechanism of LCD operation whereby liquid crystals align when a certain voltage is applied, blocking or allowing light to pass through.

Motors

  • Understand the role of motors as output devices in a control system for tasks involving movement, such as driving belts, lifting loads, or rotating items.
  • Be aware of the principle of operation of DC motors and how they convert electrical energy into mechanical energy.
  • Acknowledge different types of motors, such as servo motors, used for precision control of rotational movement, and stepper motors, used when accurate positioning is required.

Buzzers and Speakers

  • Identify buzzers and speakers as output devices employed to provide audible alerts or feedback.
  • Understand the principle of operation of these devices, where electrical signals are converted into sound waves.

Relays

  • Recognise the importance of relays, which allow a low-power electronic signal to control a high-power device.
  • Understand the concept of the relay’s coil and contacts: activating the coil magnetically closes (or opens) the contacts, thereby controlling the connected device.
  • Note the use of relays in various applications where direct control of a device is not possible or desirable, such as in high voltage applications.

Transducers

  • Understand that transducers convert one form of energy to another, a process which can be harnessed for output purposes in a control system. Examples would be a piezoelectric crystal that vibrates to produce sound, or a thermoelectric device that converts changes in temperature into a measurable electrical signal.

Printers

  • Identify printers as output devices used in systems where hard copy output of data or designs is required.
  • Be mindful of the two main types of printer used in control systems: inkjet and laser printers.