DHT11 module

DHT11 module

This DHT11 module integrates  sensor and other required components on a small PCB.  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.  It has high reliability and excellent long-term stability, thanks to the exclusive digital signal acquisition technique and temperature & humidity sensing technology. By liking Our Facebook Page Embeded Studio , you can get special discount. Data Sheet of DHT11 module can be also downloaded from the link

Each DHT11 is strictly calibrated in the laboratory that is extremely accurate on humidity calibration. The calibration coefficients are stored as programmes in the OTP memory, which are used by the sensor’s internal signal detecting process. The single-wire serial interface makes system integration quick and easy. Its small size, low power consumption and up-to-20 meter signal transmission making it the best choice for various applications, including those most demanding ones. The component is 4-pin single row pin package. It is convenient to connect and special packages can be provided according to users’ request.

The module is actually a PCB that has DHT11 component soldered with a few components, and it is a 3-wire module:

1.    VCC connected to +3.3V~5V
2.    DATA connected to the microcontroller IO port
3.    GND connected to ground

HOW TO PROCESS THE DATA

Single bus data format is used for the communication and synchronization between MCU and the DHT11 sensor. Each communication process will last about 4ms.

The data is transmitted in this format:

• 8bit integral RH data +
• 8bit decimal RH data +
• 8bit integral T data +
• 8bit decimal T data +
• 8bit check sum.

If the data transmission is correct, the check sum should equals to the lower 8bit of the result of “8bit integral RH data + 8bit decimal RH data + 8bit integral T data + 8bit decimal T data”.

The default status of the DATA pin is high. When the communication between MCU and DHT11 starts, MCU will pull down the DATA pin for least 18ms. This is called “Start Signal” and it is to ensure DHT11 has detected the signal from MCU.  Then MCU will pull up DATA pin for 20-40us to wait for DHT11’s response.

Once DHT11 detects the start signal, it will pull down the DATA pin as “Response Signal”, which will last 80us. Then DHT11 will pull up the DATA pin for 80us, and prepare for data sending.

During the data transition, every bit of data begins with the 50us low-voltage-level and ends with a high-voltage-level signal. The length of the high-voltage-level signal decides whether the bit is “0” or “1”.

Data bit “0” has 26-28us high-voltage length: