EmonTH/si7021_eval

Temperature & Humidity Sensor Evaluation and Testing

Metric	HTU21D	Si72021	DHT22	DHT22 vs HTU21D Difference	BME280
Cost in 1k off	£1.42 (July16)	£2.15	£4.57 (July16)	3.2 times cheaper (£3.15 less!)	£3.07
Vcc	2.1v - 3.6V	1.9V - 3.6V	3.3-6V		1.71 V - 3.6V
Humidity accuracy	±2% RH	±2% RH	±2%RH	n/a	±3%RH
Humidity Range	0-100% RH	0-100% RH	0-100% RH	n/a	0-100% RH
Temperature accuracy	±0.3°C	±0.4°C	±0.5°C	40% more accurate	±0.5 - ±1.0
Temperature Range	-40°C +125°C	-40°C +125°C	-40°C +80°C	56% more accurate	-40°C +80°C
Sleep Current	0.02uA	0.06uA	15uA	750 times less power	0.1uA - 0.3uA
Measurement Current	0.045mA	0.09 mA	0.5mA	11 times less power	0.714mA - 0.350mA
Measurement time	0.01s - 0.0026s	0.01s - 0.0026s	2s	200 times faster	0.013s
Energy consumed per sample	0.00045mW		1mW	2222 times less power
Time sampling per day*	14.4s		2800s
Time sleeping per day*	86386s		83600s
Energy consumed per day*	2.36mW [1]		2836mW [2]	1201 times less energy per day!

Energy consumed per day*

• HTU21D: (14.4s * 0.045mA) + (86386 * 0.00002mA) = 0.63mW + 1.73mW = 2.36mW [1]
• DHT22: (2800s * 0.55mA) + (86386 * 0.015mA) = 1540mW + 1295.8mW = 2836mW [2]

*Assuming 1 sample per min and sleeping in between samples, 1440 min per day = 86400s per day

Adafruit HTU21D Library