DHT Sensors

Humidity Sensors

Preamble

There are a number of humidity sensors on the market, but which should you choose?

DHT-11

Single-Bus DHT11 Digital, Temperature and Humidity Sensor
Single-Bus DHT11 Digital, Temperature and Humidity Sensor

Specifications from Adafruit

  • Low cost
  • 3 to 5V power and I/O
  • 2.5mA max current use during conversion (while requesting data)
  • Good for 20-80% humidity readings with 5% accuracy
  • Good for 0-50°C temperature readings ±2°C accuracy
  • No more than 1 Hz sampling rate (once every second)
  • Body size 15.5mm x 12mm x 5.5mm
  • 4 pins with 0.1″ spacing
DHT11
DHT11

DHT-22

You could go for the superior, DHT-22

DHT22 Pin Out
DHT22 Pin Out

Specifications from Adafruit

  • Low cost
  • 3 to 5V power and I/O
  • 2.5mA max current use during conversion (while requesting data)
  • Good for 0-100% humidity readings with 2-5% accuracy
  • Good for -40 to 80°C temperature readings ±0.5°C accuracy
  • No more than 0.5 Hz sampling rate (once every 2 seconds)
  • Body size 27mm x 59mm x 13.5mm (1.05″ x 2.32″ x 0.53″)
  • 4 pins, 0.1″ spacing

The two side by side

DHT Sensors
DHT Sensors

There is a selection of temperature sensors on Adafruit, which, remember, will be cheaper on eBay!

Also note that, although the two sensors may have four pins, but pin 3 is not connected, and can be just connected to ground – or indeed, the devices may only come with three pins, with pin 3 being ignored.

In addition, some sensors have pin 3 and 4 reversed, possibly as the result of a manufacturing issue. If you have issues, try grounding both pins 3 and 4.

Other Sensors

Other Sensors include DHT-21, and AM2301.

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