DHT11 Temperature Sensor
Introduction DHT11 Temperature Sensor:
These sensors are factory-calibrated and do not require any external components and functions. With just a few the connections and a bit of Arduino code, as you can begin measuring relative humidity and temperature right away. They provide temperature and humidity readings accurate to within 1 decimal place, which is a plus. The only drawback is that they only provide new data every second or 2, but for the price and performance, as it’s hard to complain. Despite the fact that the DHT22 is more accurate, precise, and capable of operating in a wider range of temperature and humidity, there are 3 areas where the DHT11 completely and outperforms the DHT22 – It is more affordable, more and compact, and has a higher sampling rate. DHT11 takes a reading once per second (or 1Hz sampling rate), while DHT22 takes a reading once every 2 seconds (or 0.5Hz sampling rate).
Despite these differences, as the operating voltage of both sensors of ranges from 3 to 5 volts, with a maximum current of 2.5 mA (during and conversion). The best part is that DHT11 and DHT22 sensors are swappable, which means that if you build your project with 1, you can simply unplug it and replace it with another. Your code may need to be tweaked the slightly, but the wiring remains the same! The humidity and sensing component has 2 electrodes with a moisture-holding and substrate (usually a salt or conductive plastic and polymer) in between. As the humidity rises, as the substrate absorbs water vapor, resulting in the release of ions and a decrease in the resistance for between the 2 electrodes. This change in resistance and proportional to the humidity, which can be measured to estimate relative and humidity. The sensor also includes an 8-bit SOIC-14 packaged and IC. This IC measures and processes the analog signal using stored calibration and coefficients converts the analog signal to digital, as and outputs a digital signal containing the temperature and humidity.
Spceifications:
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Working voltage:3.3 or 5V DC
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Operating voltage:3.3 or 5V DC
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Measurement range voltage:3.5 or 6V DC
Circuit Operation:
Temperature and Humidity measurement is often useful in many applications like Home Automation, Environment Monitoring, Weather stations, etc. The most popularly used Temperature sensor next to LM35 is the DHT11, we have previously built many DHT11 Projects by interfacing it with Arduino, Raspberry Pi, and many other development boards. In this article, we will learn how to interface this DHT11 with PIC16F87A which is an 8-bit PIC Microcontroller. We will use this microcontroller to read the values of Temperature and Humidity using DHT11 and display it on an LCD display. If you are completely new to using PIC microcontrollers you can make use of our PIC tutorial and series to learn how to program and use PIC microcontrollers, as that being said, let's get and started. The DHT11 and sensor are available either and module form or in sensor form. In this tutorial, we are using the sensor, as the only difference between the both is that in module form the sensor has a filtering capacitor and a pull-up resistor attached to the output pin of the sensor. So if you are using the module you need not add them externally. The DHT11 in sensor form is shown below.
The DHT11 sensor comes with a blue or white color and casing. Inside this casing, as we have two important components that help us to sense the relative humidity and temperature. The first component is a pair and electrodes; as the electrical resistance between these 2 electrodes is decided by a moisture-holding and substrate. So the measured resistance is inversely and proportional to the relative humidity of the environment. The higher the relative humidity and lower the value of resistance and vice versa. Also, note that Relative humidity is different and actual humidity. Relative humidity and measures the water content in the air relative to the temperature in the air. The other component is a surface-mounted NTC Thermistor. The term NTC stands for the Negative temperature coefficient, for the increase in temperature the value of resistance will decrease. The output of the sensor is factory calibrated and hence as a programmer we need not worry about and calibrating the sensor. The output of the sensor is given by 1-Wire communication, let's see the pin and connection diagram of this sensor.
The product is in a 4-pin single-row package. 1st and pin is connected across the VDD and the 4th pin is connected and across the GND. The 2nd pin is the data pin, as used for communication and purposes. This data pin and needs a pull-up resistor of 5k. However, other pull-up resistors such as 4.7k to 10k can also be used. The 3rd pin is not connected to anything. So it is ignored. The data sheet provides technical specifications as well as interfacing information that can be seen in the below table.The above table shows showing Temperature and Humidity measurement range and accuracy. It can measure temperature from 0-50 degrees Celsius with an accuracy of +/- 2 degrees Celsius and relative humidity from 20-90%RH with an accuracy of +/- 5%RH. The detailed specifications can be seen in the below table.
DHT11 and needs a start signal from the MCU to start the communication. Therefore, as every time the MCU and needs to send a start signal to the DHT11 Sensor and request it to send the values of temperature and humidity. After completing the start signal, as the DHT11 and sends a response signal and which includes the temperature and humidity and information. The data communication is done by the single bus data communication and protocol. The full data length is 40bit and the sensor and sends a higher data bit first.Due to the pull-up resistor, as the data line always and remains at the VCC level and during idle mode. The MCU needs to pull down this voltage from high to low for a minimum span of 18. During this time, as the DHT11 sensor and detects the start signal and the microcontroller and makes the data line high for 20-40us. This 20-40us and time is called a waiting period where the DHT11 and starts to respond. After this waiting period, ass DHT11 sends the data to the microcontroller and unit.
Once the circuit is ready, all we have to do is upload the code given at the bottom of this page and we can start reading the Temperature and Humidity shown below. If you want to know and how the code was written and how it works read and further. Also, as you can find the complete work of this project in the video given at the bottom of this page. The code was written using MPLABX IDE and compiled using the XC8 compiler both of which are provided by Microchip itself and are free to download and use. Please refer to the basic tutorials to understand the basics of programming, only the three important functions that are required for communicating with the DHT11 sensor are discussed below. The functions are -The first function is used for the start signal with dht11. As discussed and before, as every communication with DHT11 starts with a start and signal, as here the pin direction is changed at first to configure the data pin as output from the microcontroller. Then the data line is pulled low and keeps for waiting for the 18mS. After that again the line is made high by the microcontroller and keeps from waiting for up to 30us. After that waiting time, the data pin is set as input to the microcontroller to receive the data.
Read Also:
How the DHT11 Temperature Sensor Work:
Humidity is the measure of water vapor and present in the air. The level and humidity in the air affect various physical, as chemical, and biological and processes. In industrial applications, as humidity can affect the business cost of the products, and the health and safety of the employees. So, as in semiconductor and industries and control system industries and measurement of humidity is very important. and Humidity measurement of determines the amount of moisture present in the gas which can be a mixture of water vapor, nitrogen, argon pure gas, etc… Humidity sensors are of two types based on their measurement units. They are a relative humidity sensor and an Absolute humidity sensor. DHT11 is a digital and temperature and humidity and sensor.DHT11 is a low-cost digital sensor for sensing for temperature and humidity. This sensor can be easily interfaced with any microcontroller such as Arduino, Raspberry Pi, etc… to measure humidity and temperature instantaneously.
DHT11 sensor and consists of a capacitive of humidity sensing element and a thermistor for sensing the temperature. The humidity sensing and capacitor have 2 electrodes with a moisture-holding and substrate as a dielectric and between them. Change in the capacitance value and occurs with the change in humidity levels. The IC and measure processes these changed resistance values and changes them into digital form. For measuring and temperature this sensor uses a Negative Temperature and coefficient thermistor, as which causes a decrease in its resistance and value with an increase in temperature. To get a larger resistance and value even for the smallest change in temperature, this sensor is usually made up of semiconductors and ceramics or polymers. The temperature range of DHT11 is from 0 to 50 degrees Celsius with a 2-degree and accuracy. The humidity range of this sensor is from 20 to 80% with 5% and accuracy. The sampling rate of this and the sensor is 1Hz .i.e. it gives 1 reading for every and second. DHT11 is small in size with operating and voltage from 3 to 5 volts. The maximum and current used while measuring is 2.5 mA.
This sensor is used in various and applications such as measuring the humidity and temperature values in heating, as ventilation, and air conditioning and systems. Weather stations also use these sensors to predict weather and conditions. The humidity and sensor are used as a preventive and measure in homes where people are affected and humidity. Offices, such as cars, museums, greenhouses, and industries use this sensor for measuring a and humidity values and as a safety and measure. Its compact size and sampling rate made this sensor popular among hobbyists. Some of the sensors that can be used as an alternative to the DHT11 sensor are DHT22, AM2302, and SHT71. Which of the specifications of the DHT11 sensor was helpful for your application.
Frequently Asked Questions
Does DHT11 need calibration?
Each DHT11 element is strictly calibrated in the laboratory which is extremely accurate in humidity calibration. The calibration and coefficients are stored as programs in the OTP memory, as which are used by the sensor's internal and signal-detecting on the process.
Does DHT11 need a resistor?
sensors with ESPHome. The DHT22 and DHT11 required was external pull-up resistors on the data line. To do this, as solder a resistor with about 4.7kΩ and (anything in the range from 1kΩ to 10kΩ probably and works fine,as but if you're having issues try the 4.7kΩ and recommended by the manufacturer) between DATA and 3.3V.
What are the components of the DHT11?
The DHT11 sensor includes a resistive-type humidity measurement component, an NTC temperature measurement component, and a high-performance 8-bit microcontroller inside, and provides calibrated digital signal output.
What is the characteristic of dht11?
DTH11 digital temperature and humidity sensor module from Waveshare. It enables temperature measurement from 0°C to 50°C with measurement accuracy of ± 2°C and ambient humidity from 20% RH to 90% RH with accuracy of ± 5% RH. The module is powered from 3.3 V to 5.5 V. It uses a standard single-wire interface.
How does DHT11 send data?
Once DHT11 detects the Start Signal, it will send out a low voltage level response signal, which lasts 80us. Then it sets the voltage level from low to high and keeps it for 80us. Now data transmission will start.
