Here are the pin outs for both versions: How to Set Up the DHT11 on an Arduino The PCB mounted version is nice because it includes a surface mounted 10K Ohm pull up resistor for the signal line. One type has four pins, and the other type has three pins and is mounted to a small PCB.
There are two different versions of the DHT11 you might come across. A 10K Ohm pull-up resistor is needed between the signal line and 5V line to make sure the signal level stays high by default (see the datasheet for more info). Power comes from separate 5V and ground wires. The DHT11 uses just one signal wire to transmit data to the Arduino. With the plastic housing removed, you can see the electrodes applied to the substrate:Īn IC mounted on the back of the unit converts the resistance measurement to relative humidity. It also stores the calibration coefficients, and controls the data signal transmission between the DHT11 and the Arduino: To learn more about how thermistors work and how to use them on the Arduino, check out our Arduino Thermistor Temperature Sensor Tutorial. The DHT11 measures temperature with a surface mounted NTC temperature sensor (thermistor) built into the unit. Higher relative humidity decreases the resistance between the electrodes, while lower relative humidity increases the resistance between the electrodes. The change in resistance between the two electrodes is proportional to the relative humidity. When water vapor is absorbed by the substrate, ions are released by the substrate which increases the conductivity between the electrodes.
The DHT11 detects water vapor by measuring the electrical resistance between two electrodes. The humidity sensing component is a moisture holding substrate with electrodes applied to the surface. How the DHT11 Measures Humidity and Temperature At 100% RH, condensation occurs, and at 0% RH, the air is completely dry. Relative humidity is expressed as a percentage. The formula to calculate relative humidity is: Cold air can hold less water vapor before it becomes saturated, and hot air can hold more water vapor before it becomes saturated. The saturation point changes with air temperature. At the saturation point, water vapor starts to condense and accumulate on surfaces forming dew. the saturation point of water vapor in air. Relative humidity is the amount of water vapor in air vs. Here are the ranges and accuracy of the DHT11:ĭHT11 Datasheet What is Relative Humidity? It includes all of the parts, wiring diagrams, code, and step-by-step instructions for 58 different robotics and internet of things projects that are super fun to build! The 3-in-1 Smart Car and IOT Learning Kit from SunFounder has everything you need to learn how to master the Arduino.
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