Electronic systems mainly use sensors and switches as input devices. Sensors detect changes in physical conditions, while switches allow an electrical input to be activated, deactivated, or selected.
How input devices work
An electronic system can be represented using the input-process-output model. The input device supplies a signal to a processor or control circuit, which makes a decision and controls an output such as a motor, lamp, buzzer, or display.
A sensor is an input transducer: it converts a physical quantity into an electrical signal. For example, a thermistor responds to temperature, while a light-dependent resistor responds to light intensity. The signal may require signal conditioning, such as amplification or conversion from an analogue signal into digital data, before a microcontroller can process it.
A switch changes the state of a circuit. It usually produces a digital signal with two possible states: on or off, often represented as logic high and logic low.
| Input device | Function and typical application |
|---|---|
| Thermistor | Detects temperature, for example in an automatic heating system |
| Light-dependent resistor (LDR) | Detects light intensity, for example in automatic lighting |
| Pressure or force sensor | Detects applied pressure or force, for example in a safety mat |
| Microphone | Converts sound waves into an electrical signal |
| Push-button switch | Provides momentary manual input, such as starting a machine |
| Toggle switch | Maintains a selected on or off state |
| Limit switch | Detects when a moving component reaches a fixed position |
| Reed switch | Responds to a magnetic field, for example in a door alarm |
The common misconception is that every sensor produces a simple on-or-off output. Many sensors produce a continuously varying , whereas switches normally provide discrete digital input.
