563  Sensor Selection Reference Guide

Complete Technical Specifications for 12 Common IoT Sensors

563.1 Learning Objectives

By studying this reference guide, you will be able to:

  1. Identify key specifications for temperature, humidity, pressure, gas, light, distance, and motion sensors
  2. Compare sensor characteristics including accuracy, cost, power, and lifespan
  3. Recognize when each sensor type is appropriate for specific applications
  4. Understand the trade-offs between low-cost consumer and industrial-grade sensors

When evaluating sensors, focus on these key specifications:

Specification What It Means Example
Range Min/max values the sensor can measure -40 to +125°C
Accuracy How close readings are to true value ±0.1°C
Resolution Smallest change sensor can detect 0.01°C
Power Consumption Current draw during operation 3.4 µA
Interface Communication protocol I2C, SPI, analog
Lifespan Expected operating life 10 years

Tip: Higher accuracy sensors cost more. Match sensor precision to your actual requirements.

563.2 Environment Sensors

563.2.1 DHT22 (Temperature & Humidity)

Category: Environment | Cost: $5 | Lifespan: 2-3 years

Specification Value
Temperature Range -40 to 80°C
Temperature Accuracy ±0.5°C
Humidity Range 0-100% RH
Humidity Accuracy ±2% RH
Power Consumption 1.5 mA active
Response Time 2 seconds
Interface 1-Wire digital
Calibration Factory calibrated

Pros:

  • Very low cost
  • Integrated temp + humidity
  • Simple 1-Wire interface
  • Good accuracy (±0.5°C, ±2% RH)

Cons:

  • Short lifespan
  • Slow response (2 seconds)
  • Drifts over time
  • Not industrial-grade

Best For: Hobbyist projects, indoor monitoring, low-budget applications

563.2.2 Sensirion SHT85

Category: Environment | Cost: $25 | Lifespan: 10+ years

Specification Value
Temperature Range -40 to 125°C
Temperature Accuracy ±0.1°C
Humidity Range 0-100% RH
Humidity Accuracy ±1.5% RH
Power Consumption 0.6 mA active
Response Time 8 seconds
Interface I2C digital
Calibration Factory calibrated, stable

Pros:

  • Excellent accuracy (±0.1°C, ±1.5% RH)
  • Factory-calibrated, stable
  • Wide temperature range (-40 to +125°C)
  • Industrial-grade reliability

Cons:

  • Higher cost (5x DHT22)
  • Slower response than thermocouples

Best For: Industrial monitoring, HVAC control, outdoor weather stations, cleanrooms

563.2.3 Bosch BMP388

Category: Pressure | Cost: $8 | Lifespan: 10 years

Specification Value
Pressure Range 300-1250 hPa
Pressure Accuracy ±0.33 hPa
Temperature Range -40 to 85°C
Temperature Accuracy ±0.5°C
Power Consumption 3.4 µA @ 1Hz
Response Time Instant
Interface I2C/SPI
Calibration Factory calibrated

Pros:

  • High precision (±0.33 hPa)
  • Ultra-low power (3.4 µA)
  • Small footprint
  • Temperature-compensated

Cons:

  • Limited pressure range
  • Temperature drift needs compensation
  • MEMS sensitive to shock

Best For: Weather stations, altitude measurement, battery-powered IoT devices

563.3 Gas Sensors

563.3.1 MQ-135 (Air Quality)

Category: Gas | Cost: $3 | 5-Year TCO: $406

Specification Value
Detects CO2, NH3, NOx, Benzene
Sensitivity 10-1000 ppm (varies)
Accuracy ±20-50% (uncalibrated)
Power Consumption 150 mA (heater)
Response Time 30 seconds
Interface Analog voltage
Lifespan 1-2 years
Calibration Regular calibration required

Cost Breakdown (5-Year):

  • Initial cost: $3
  • Annual calibration: $50/year × 5 = $250
  • Replacements (every 2 years): $6
  • Annual maintenance: $20/year × 5 = $100
  • Total 5-Year TCO: ~$406

Pros:

  • Very low initial cost
  • Detects multiple gases
  • Simple analog output

Cons:

  • Poor accuracy (±20-50%)
  • High power (150 mA heater)
  • Frequent calibration ($50/year)
  • Short lifespan (1-2 years)

Best For: General air quality indication (not safety-critical)

WarningTCO Warning

Despite $3 initial cost, MQ-135 has $406 total cost over 5 years due to calibration and replacement. Always calculate TCO!

563.3.2 CCS811 (eCO2/TVOC)

Category: Gas | Cost: $12 | Lifespan: 3-5 years

Specification Value
Detects eCO2, TVOC
eCO2 Range 400-8192 ppm
TVOC Range 0-1187 ppb
Accuracy ±50 ppm (eCO2)
Power Consumption 1.2 mA active
Response Time 60 seconds
Interface I2C digital
Calibration Baseline calibration

Pros:

  • Digital I2C output
  • Low power compared to MQ series
  • Measures both eCO2 and TVOC

Cons:

  • Estimated CO2 (not true NDIR measurement)
  • Baseline drift requires recalibration
  • Not suitable for safety-critical applications

Best For: Indoor air quality, smart HVAC, energy-efficient monitoring

563.3.3 Sensirion SCD40 (True CO2)

Category: Gas | Cost: $50 | Lifespan: 10+ years

Specification Value
Detects CO2 (NDIR)
CO2 Range 400-2000 ppm
Accuracy ±40 ppm ±5%
Power Consumption 18 mA active
Response Time 60 seconds
Interface I2C digital
Calibration Auto-calibration

Pros:

  • True NDIR CO2 measurement
  • High accuracy (±40 ppm)
  • Auto-calibration
  • Long-term stability (10+ years)

Cons:

  • Higher cost ($50)
  • Slower response (60 seconds)
  • Requires periodic baseline

Best For: Accurate CO2 monitoring, HVAC ventilation control, regulatory compliance, research

NoteNDIR vs eCO2

True NDIR sensors (SCD40) measure CO2 directly using infrared absorption. eCO2 sensors (CCS811) estimate CO2 from VOC measurements and are less accurate.

563.4 Light Sensors

563.4.1 BH1750 (Ambient Light)

Category: Light | Cost: $2 | Lifespan: 10 years

Specification Value
Range 1-65535 lux
Accuracy ±20% typical
Spectral Response Close to human eye
Power Consumption 120 µA active
Response Time 120 ms
Interface I2C digital
Calibration Factory calibrated

Pros:

  • Very low cost ($2)
  • Wide range (1-65535 lux)
  • Ultra-low power (120 µA)
  • Human eye spectral response

Cons:

  • ±20% accuracy
  • Saturates in direct sunlight (>65k lux)
  • Temperature drift

Best For: Automatic lighting control, display brightness adjustment, energy saving

563.4.2 TSL2591 (High-Dynamic Light)

Category: Light | Cost: $8 | Lifespan: 10+ years

Specification Value
Range 0.000188-88000 lux
Accuracy ±10% typical
Channels Visible + IR
Power Consumption 400 µA active
Response Time 100 ms
Interface I2C digital
Calibration Factory calibrated

Pros:

  • Ultra-wide dynamic range (0.000188-88000 lux)
  • Separate visible + IR channels
  • Better accuracy (±10%)
  • Programmable gain

Cons:

  • 4x more expensive than BH1750
  • Complex configuration
  • IR compensation needed

Best For: Outdoor monitoring, solar panel tracking, research applications, wide-range applications

563.5 Distance Sensors

563.5.1 HC-SR04 (Ultrasonic Distance)

Category: Distance | Cost: $2 | 5-Year TCO: $52

Specification Value
Range 2-400 cm
Accuracy ±3 mm
Beam Angle 15°
Power Consumption 15 mA active
Response Time Trigger-based
Interface Digital pulse
Lifespan 3-5 years
Calibration Temperature compensation

Pros:

  • Very low cost ($2)
  • Long range (2-400 cm)
  • Simple trigger/echo interface
  • Good accuracy (±3 mm)

Cons:

  • Temperature sensitive (needs compensation)
  • Soft materials absorb ultrasound
  • Narrow beam (15°)
  • Outdoor interference (wind)

Best For: Object detection, parking sensors, tank level measurement, robotics

563.5.2 VL53L1X (ToF Distance)

Category: Distance | Cost: $15 | Lifespan: 10+ years

Specification Value
Range 40-4000 mm
Accuracy ±25 mm @ 3m
Field of View 27°
Power Consumption 19 mA active
Response Time 20-50 ms
Interface I2C digital
Calibration Factory calibrated

Pros:

  • Immune to ambient light
  • Fast response (20-50 ms)
  • Temperature-stable
  • Precise (±25 mm @ 3m)

Cons:

  • Shorter range than ultrasonic
  • Affected by surface reflectivity
  • Higher cost ($15)

Best For: Precise ranging, gesture detection, industrial automation, drones, obstacle avoidance

563.6 Motion Sensors

563.6.1 MPU-6050 (6-Axis IMU)

Category: Motion | Cost: $5 | Lifespan: 5-7 years

Specification Value
Accelerometer ±2/4/8/16g
Gyroscope ±250/500/1000/2000°/s
Accuracy ±1% (accel), ±3% (gyro)
Power Consumption 3.9 mA active
Output Rate 1 kHz
Interface I2C digital
Calibration Gyro drift compensation

Pros:

  • Very low cost ($5)
  • Integrated accel + gyro
  • Low power (3.9 mA)
  • Integrated DMP processor

Cons:

  • Gyro drift over time
  • Temperature sensitive
  • Consumer-grade accuracy
  • No absolute heading

Best For: Motion tracking, gaming controllers, drones, wearables, step counting

563.6.2 BNO055 (9-Axis Fusion)

Category: Motion | Cost: $30 | Lifespan: 10 years

Specification Value
Sensors Accel + Gyro + Mag
Orientation Absolute (Euler/Quaternion)
Heading Accuracy ±1°
Power Consumption 12.3 mA active
Fusion Rate 100 Hz
Interface I2C/UART
Calibration Auto-calibration

Pros:

  • Absolute orientation (±1°)
  • Sensor fusion (accel + gyro + mag)
  • Auto-calibration
  • 100 Hz fusion output

Cons:

  • Higher cost (6x MPU-6050)
  • Magnetic interference
  • Higher power (12.3 mA)

Best For: Robotics, AR/VR, navigation, industrial automation, SLAM

563.7 Sensor Comparison Summary

Sensor Category Cost Accuracy Power Lifespan Best For
DHT22 Temp/Humidity $5 ±0.5°C 1.5 mA 2-3 yr Hobbyist
SHT85 Temp/Humidity $25 ±0.1°C 0.6 mA 10+ yr Industrial
BMP388 Pressure $8 ±0.33 hPa 3.4 µA 10 yr Weather
MQ-135 Gas $3 ±20-50% 150 mA 1-2 yr Indication only
CCS811 eCO2/TVOC $12 ±50 ppm 1.2 mA 3-5 yr Smart HVAC
SCD40 True CO2 $50 ±40 ppm 18 mA 10+ yr Compliance
BH1750 Light $2 ±20% 120 µA 10 yr Lighting control
TSL2591 Light $8 ±10% 400 µA 10+ yr Solar tracking
HC-SR04 Distance $2 ±3 mm 15 mA 3-5 yr Parking
VL53L1X Distance $15 ±25 mm 19 mA 10+ yr Drones
MPU-6050 Motion $5 ±3% 3.9 mA 5-7 yr Wearables
BNO055 Motion $30 ±1° 12.3 mA 10 yr Robotics

563.8 Summary

When selecting sensors, remember these key principles:

  1. Match accuracy to requirements - Don’t over-specify. A $5 sensor is often sufficient.
  2. Calculate 5-year TCO - Include replacements, maintenance, and calibration costs.
  3. Consider power constraints - Battery applications need ultra-low power sensors.
  4. Check environmental ratings - Indoor sensors fail outdoors.
  5. Verify interface compatibility - Ensure your MCU supports the sensor’s protocol.

563.9 What’s Next