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si7021
readme.md

readme.md

Temperature & Humidity Sensor Evaluation and Testing

Metric HTU21D Si72021 DHT22 DHT22 vs HTU21D Difference BME280
Cost in 1k off £2.15 £4.57 (July16) 3.2 times cheaper (£3.15 less!) £3.07
Vcc 1.9V - 3.6V 3.3-6V 1.71 V - 3.6V
Humidity accuracy ±2% RH ±2%RH n/a ±3%RH
Humidity Range 0-100% RH 0-100% RH n/a 0-100% RH
Temperature accuracy ±0.4°C ±0.5°C 40% more accurate ±0.5 - ±1.0
Temperature Range -40°C +125°C -40°C +80°C 56% more accurate -40°C +80°C
Sleep Current 0 0.06uA 15uA 750 times less power 0.1uA - 0.3uA
Measurement Current 0. 0.09 mA 0.5mA 11 times less power 0.714mA - 0.350mA
Measurement time 0.01s 0.01s - 0.0026s 2s 200 times faster 0.013s
Energy consumed per sample 2.97uJ 3300uJ 2000 times less power
Time sampling per day* 2800s
Time sleeping per day* 83600s
Energy consumed per day* 8700mJ [2] 1115 times less energy per day!
energy consumed (joule, J) = potential difference (volt, V) × charge (coulomb, C)
charge (coulomb, C) = current (ampere, A) × time (second, s)
energy consumed (joule, J)  = potential difference (volt, V) × current (ampere, A) × time (second, s)

Energy consumed per day*

Energy consumed per day = energy consumed per sample + energy consumed while sleeping.

  • HTU21D: (1400 * 0.0015mJ) + (3.3V * 0.00002mA * 86386 ) = 2.1mJ + 5.7mJ = 7.8mJ [1]
  • DHT22: (1400 * 3.3mJ) + (3.3V * 0.015mA * 83600) = 4.6mJ + 4.1J = 8.7J = 8700mJ [2]

*Assuming 1 sample per min and sleeping in between samples: 1400 samples per day

Adafruit HTU21D Library