This project is about a simple humidity sensor based on 8051 microcontroller. Humidity sensor is also called hygrometer. This circuit can sense relative humidity (RH) from 20% to 95% at an accuracy of 5%. The humidity information is displayed on a 16×2 LCD display. A relay is also provided which is set to be active when the humidity crosses a certain trip point. The circuit is mains operated and it is very easy to install. DHT11 is the humidity sensor used here. The details and working of the DHT11 humidity sensor is given below.
DHT11 is a low cost humidity cum temperature sensor which has a digital output. Capacitive method is used for sensing the humidity and a thermistor is used for measuring the temperature. The sensor can sense relative humidity from 20% to 95% at a resolution of 5%. Temperature measurement is up to 50°C at a resolution of 2°C. The communication with the microcontroller is through a single wire. The basic communication scheme is given in the image below.
The to and fro communication with DHT11 sensor is very easy. Pin 2 of the DHT11 is connected to the port pin of the micrcontroller. The connection scheme is shown in the image below. The data pin (pin2) of the DHT11 requires an external 10K pull-up resistor.
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