Input devices
An input device responds to changes in the environment and produces a suitable electrical signal for processing in an electronic circuit.
In all input devices, other forms of energy are transformed into electrical energy.
Below are some common input devices with examples of how they might be used.
Microphone
A microphone generates a voltage when sound reaches it. It is used in a telephone or an intercom.
Thermistor
Its resistance increases when the temperature falls. Is used as a sensor in heating systems.
Solar cell or photo-voltaic cell
Produces a voltage when light falls on it, provides energy for satellites.
Light dependent resistor (LDR)
Resistance decreases as light level rises. Used to control street lights.
Capacitor
Used in timing circuits and electronic amplifiers.
Switch
Allows current in a circuit when closed. Used to switch on circuits.
Voltage divider
To create a voltage across the bottom component that can then be sent to a process device. Used in devices, eg mosfets or npn transistors, where a voltage change switches on or off a circuit.
