536  Sensor Classifications

Learning Objectives

After completing this chapter, you will be able to:

  • Classify sensors by measurement type (environmental, motion, chemical, biometric)
  • Understand output types (analog, digital, I2C, SPI, UART)
  • Distinguish between active and passive sensors
  • Choose appropriate sensor interfaces for your project

536.1 Prerequisites

536.2 Sensor Classifications

~15 min | Intermediate | P06.C08.U03

536.3 By Measurement Type

Understanding how sensors are classified by measurement type helps engineers select the right sensor for each IoT application.

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mindmap
  root((Sensor Types<br/>by Measurement))
    Environmental
      Temperature
      Humidity
      Pressure
      Air Quality
      Light
    Motion & Position
      Accelerometer
      Gyroscope
      Magnetometer
      GPS
      Proximity
    Physical
      Force
      Torque
      Strain
      Vibration
      Acoustic
    Chemical
      Gas sensors
      pH sensors
      Conductivity
      Electrochemical
    Biometric
      Heart rate
      SpO2
      ECG
      Temperature
      Glucose

536.3.1 Environmental Sensors

Sensor Type What It Measures Common Models Typical Accuracy
Temperature Thermal energy DHT22, DS18B20, BME280 +/-0.5C
Humidity Moisture in air DHT22, SHT31, BME280 +/-2-3% RH
Pressure Atmospheric pressure BMP280, MS5611 +/-1 hPa
Light Ambient illumination BH1750, TSL2561 +/-5% lux
Air Quality CO2, VOCs, particulates MQ-135, BME680, PMS5003 Varies

536.3.2 Motion and Position Sensors

Sensor Type What It Measures Common Models Applications
Accelerometer Linear acceleration ADXL345, MPU6050 Step counting, tilt
Gyroscope Angular velocity MPU6050, L3GD20 Rotation, orientation
Magnetometer Magnetic field HMC5883L, QMC5883 Compass, heading
GPS Geographic position NEO-6M, NEO-M8N Location tracking
Proximity Object presence HC-SR04, VL53L0X Distance, presence

536.3.3 Chemical and Gas Sensors

Sensor Type What It Detects Common Models Notes
CO2 Carbon dioxide MH-Z19, SCD30 NDIR or electrochemical
VOC Volatile organics BME680, SGP30 Air quality index
Smoke/Gas Combustible gases MQ-2, MQ-5 Requires 24-48h burn-in
pH Acidity/alkalinity pH probe + ADC Needs regular calibration

536.4 By Output Type

Output Type Description Interface Example Sensors
Analog Continuous voltage/current signal ADC required LM35 (temp), LDR (light), Flex sensor
Digital Discrete HIGH/LOW states GPIO PIR motion, reed switch, IR obstacle
PWM Pulse width modulated signal Timer/counter Some humidity sensors
I2C Two-wire serial protocol I2C bus BMP280, MPU6050, Si7021
SPI Four-wire serial protocol SPI bus MAX31855, LSM9DS1
UART Serial asynchronous communication UART/Serial GPS modules, PM2.5 sensors
1-Wire Single-wire protocol 1-Wire interface DS18B20 temperature

536.4.1 Choosing the Right Interface

TipInterface Selection Guide

Use Analog when: - Simple, low-cost sensors (photoresistors, thermistors) - Need custom signal conditioning - Only one or few sensors

Use I2C when: - Multiple sensors sharing a bus - Need built-in calibration - Standard breakout boards

Use SPI when: - High-speed data transfer needed - Multiple sensors with chip-select - Signal integrity critical

Use UART when: - Smart sensors with built-in processing - GPS modules, particulate sensors - Long-distance communication needed

536.5 By Power Requirement

Type Characteristics Examples Use Cases
Active Sensors Require external power, emit energy Radar, ultrasonic, active RFID Distance measurement, object detection
Passive Sensors Detect existing energy, low power Thermistors, LDR, passive IR Battery-powered applications
TipTradeoff: Wired vs Wireless Sensors

Wired Sensors (Ethernet, RS-485, 4-20mA): - Reliable, no interference - No battery replacement - Higher installation cost - Fixed location

Wireless Sensors (Wi-Fi, LoRa, Zigbee, BLE): - Flexible placement - Lower installation cost - Battery replacement required - Potential interference

Choose wired for: Industrial environments, critical measurements, permanent installations

Choose wireless for: Retrofits, temporary installations, hard-to-wire locations

536.6 Sensor Types by Application Domain

Domain Common Sensors Key Requirements
Smart Home Temperature, humidity, motion, door/window Low power, easy setup
Industrial IoT Vibration, temperature, pressure, current Rugged, accurate, reliable
Agriculture Soil moisture, temperature, light, weather Outdoor-rated, long battery
Healthcare Heart rate, SpO2, temperature, glucose Medical-grade accuracy
Automotive Accelerometer, gyroscope, GPS, radar Fast response, safety-critical

536.7 Summary

Key classification takeaways:

  1. Match measurement type to application - Environmental, motion, chemical, or biometric
  2. Choose interface wisely - Analog for simple, I2C/SPI for digital, UART for smart sensors
  3. Consider power requirements - Active vs passive impacts battery life
  4. Wired vs wireless - Based on installation constraints and reliability needs

536.8 What’s Next

Now that you understand sensor classifications:

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