GPIO - Measure Temperature And Humidity
DHT11 is a temperature and humidity sensor which operates at voltage 3.3V~5V. At room temperature, the measurable range of the humidity is 20% ~ 90%RH with ±5%RH precision, the measurable range of the temperature is 0 ~ 50℃ with ±2℃ precision.
Another choice of temperature and humidity sensor is DHT22 sensor, which has better precision. Its measurable range of the humidity is 0%~100%RH with ±5%RH precision, the measurable range of the temperature is -40~125 ℃ with ±0.2℃ precision.
There are 4 pins on the sensor:
Since one of the 4 pins has no function, there are temperature/humidity sensors with only 3 pins on the market:
DHT is normally in the sleeping mode. To get the temperature/humidity data, please follow the steps:
- Awake DHT: Ameba toggles low its DATA pin of GPIO. Now the DATA pin of GPIO serves as digital out to Ameba.
- DHT response: DHT also toggle low its DATA pin of GPIO. Now the DATA pin of GPIO serves as digital in for Ameba.
- DHT sends data: DHT sends out the temperature/humidity data (which has size 5 bytes) in a bit by bit manner. To represent each bit, DHT first pull low the DATA GPIO pin for a while and then pull high. If the duration of high is smaller than low, it stands for bit 0. Otherwise it stands for bit 1.
AMB21/ AMB22 wiring diagram:
AMB23 wiring diagram:
BW16 wiring diagram:
Open the sample code in “Files” -> “Examples” -> “AmebaGPIO” -> “DHT_Tester”. Compile and upload to Ameba, then press the reset button. The result would be shown on the Serial Monitor.
dht.readHumidity()read the humidity value, and use
dht.readTemperature()to read the temperature value.