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What a sensor actually is

A sensor responds to something physical, like heat or force, in a way a circuit can measure. Every reading depends on how well it does that.

Foundation

What a sensor does, and two ways its reading reaches a microcontroller A sensor responds to a physical quantity and produces or changes an electrical one. An analog sensor needs an ADC before the microcontroller; a digital sensor has the ADC and processing built in and reports over a digital bus such as I²C or SPI. Self-generating sensors make their own signal; modulating sensors need an external voltage or current. Physical quantity temperature, force, light or motion Sensor responds directly to it Electrical quantity produces or changes a voltage, charge or resistance Two ways to reach the microcontroller Analog sensor analog signal ADC Digital sensor sensor, ADC and signal processing in one part digital bus such as I²C or SPI Microcontroller Self-generating Thermocouple signal Makes its signal from the quantity. Modulating Strain gauge, RTD signal needs an external voltage or current Some books call these 'passive' and 'active', but not consistently.
A sensor responds to a physical quantity and produces or changes an electrical one; an analog sensor needs an ADC, while a digital sensor reports over a digital bus such as I²C or SPI.

Key points

  1. A sensor is the part of a measuring system that responds directly to something physical, such as temperature, force, light or motion. A device whose output has a known relationship to its input is a transducer. Sensors in electronics produce or change an electrical quantity, such as a voltage, charge or resistance.123
  2. Some sensors output an analog signal that still needs an ADC; others integrate the ADC and signal processing and report readings over a digital bus such as I²C or SPI.245
  3. Self-generating sensors, such as thermocouples, produce a signal from the quantity they measure. Modulating sensors, such as strain gauges and RTDs, need an external voltage or current to work. Some books call these 'passive' and 'active', but not consistently.6273

Common mistakes

  • Trusting the first reading. Most sensors drift with temperature and time, so check how much error to expect.

Where to go next

Sources

  1. JCGM 200:2012 International vocabulary of metrology (VIM), 3rd edition · BIPM · Standard
  2. A Basic Guide to Thermocouple Measurements (SBAA274A) · Texas Instruments · Reference
  3. A Basic Guide to RTD Measurements (SBAA275A) · Texas Instruments · Reference
  4. LIS2DW12 datasheet (ST DocID029682 Rev 4) · STMicroelectronics · Datasheet
  5. UM10204: I2C-bus specification and user manual · NXP · Standard
  6. Expanding the Vision of Sensor Materials, Appendix C: An Illustrative Sensor Taxonomy · National Research Council (National Academies Press), 1995 · Reference
  7. A Basic Guide to Bridge Measurements (SBAA532A) · Texas Instruments · Reference