# DHT11/DHT22

![steps](/docs/dht11_22_steps.png)

## Step 1

After powering on the DHT11/DHT22 (once powered, allow 1 second to pass during which the sensor stabilizes; during this time, no commands should be sent), it measures the temperature and humidity of the surrounding environment and stores the data. Meanwhile, the DATA line of the DHT11/DHT22 is kept high by a pull-up resistor. The DATA pin of the DHT11/DHT22 is in input mode, ready to detect any external signals.

## Step 2

The microprocessor's I/O pin is set to output mode and pulled low, holding this state for at least 18 milliseconds. Then, the microprocessor's I/O is switched to input mode. Due to the pull-up resistor, the microprocessor’s I/O line and the DHT11/DHT22 DATA line will remain high, waiting for the DHT11/DHT22 to respond with a signal, as illustrated below:

![step2](/docs/dht11_22_step2.png)


## Step 3

The DHT11/DHT22’s DATA pin detects an external signal and goes low, indicating that it is waiting for the external signal to complete. Once the signal ends, the DHT11/DHT22’s DATA pin switches to output mode, producing a low signal for 80 microseconds as a response. This is followed by an 80-microsecond high signal, notifying the microprocessor that the sensor is ready to transmit data. At this point, the microprocessor's I/O pin, still in input mode, detects the low signal from the DHT11/DHT22 (indicating the response) and then waits for the 80-microsecond high signal to start receiving data. The sequence of signal transmission is illustrated below:

![step3](/docs/dht11_22_step3.png)

## Step 4

The DHT11/DHT22 outputs 40 bits of data through the DATA pin, and the microprocessor receives these 40 data bits. The format for a data bit "0" consists of a low level lasting 50 microseconds, followed by a high level lasting 26-28 microseconds, depending on changes in the I/O level. For a data bit "1," the format includes a low level of 50 microseconds followed by a high level lasting up to 70 microseconds. The signal formats for data bits "0" and "1" are shown below.

![step4](/docs/dht11_22_step4.png)

## End signal

After outputting a low signal for 50 microseconds, the DHT11/DHT22 completes sending the 40 bits of data and switches the DATA pin back to input mode, which, along with the pull-up resistor, returns to a high state. Meanwhile, the DHT11/DHT22 internally re-measures the environmental temperature and humidity, records the new data, and waits for the next external signal.