Sensor

A sensor measures a physical quantity (temperature, light, motion, pressure, gas, distance) and outputs a signal — analog voltage, digital pulse, I²C/SPI data, or a frequency the system can interpret.

Different sensors use different physics: a thermistor changes resistance with temperature; a photodiode produces current under light; a MEMS accelerometer measures the deflection of a tiny silicon spring; an ultrasonic sensor times the round-trip of a click.

In plain terms

Five senses for your microcontroller. Each sensor is one of those senses translated into electricity.

Also called: transducer.

Why designers use it

Read the environment so firmware can decide what to do.
Close the loop on motion control or temperature regulation.
Detect human presence, gestures, or biometric signals.
Provide telemetry to dashboards and alerts.

Best for

Environmental monitoring
Human-machine interfaces
Industrial control loops
Health and fitness wearables

When not to use it

Where a simple switch or threshold would do — sensors add complexity and cost.
Where firmware can't handle the noise or calibration the sensor demands.

Common mistakes

Skipping the data-sheet recommended decoupling and seeing noise dominate the measurement.
Mounting a temperature sensor where the MCU's heat dwarfs the signal.
Forgetting to calibrate — raw sensor counts ≠ engineering units.

Where you will find it

A resistive sensing element can be placed in a divider or bridge so its resistance change becomes a measurable voltage.
A measurement chain may combine a sensor, conditioning electronics and an ADC. Each stage contributes its own limits.

A short history

A sensor links a physical quantity to an electrical response. Comparing sensors requires more than counting output bits: sensitivity, input range, uncertainty, noise, resolution and bandwidth describe different parts of measurement performance. The surrounding signal-conditioning circuit can also limit the result.

Good to know

Sensitivity describes how much the output changes for a small input change; it is not the same as accuracy.
A sensor's response time matters when the physical signal changes quickly.
The smallest detectable change depends on noise and the measurement bandwidth.