Abstract

In our daily life it is sometimes necessary to measure the temperature and humidity of the environment around us. Many kinds of sensors for measuring temperature or humidity, such as LM35, DS18S20 or DHT11. To measure the temperature and humidity of the environment around us, we can choose a sensor that is quite cheap, namely DHT11. DHT11 has a calibrated digital output. This sensor consists of resistive type humidity measuring components and temperature measurements via NTC and is connected with 8 bit uC so that it gives good results, sufficient response speed, has good resistance to interference and is quite cheap in price. The interface used is a single write serial interface which is quite fast and easy. Small sensor size, low power consumption requirements and able to transmit its output within a distance of 20 meters. The disadvantage of this sensor is the lack of accuracy, besides the temperature measurement range is only 0 to 50 degrees Celsius but with a fairly cheap price this sensor can be an alternative to be used in temperature and humidity measurements that do not really need good accuracy. For example measurement of room temperature, measurement of temperature and humidity of incubators and others. If the sensor distance to the uC is less than 20 meters, then a 5K pull up resistor must be installed on the data pin. Meanwhile, if the distance is more than 20 meters, then the size of the pull up resistor should be adjusted. The power supply needed by DHT11 ranges from 3.5V to 5V. Access to the sensor is only allowed more than 1 second after the first power supply is supplied. It is also necessary to add a 100nF capacitor between the VCC and GND pins for the power supply filter.