FPGA collects DHT11 temperature and humidity

One . brief introduction

In the temperature and humidity sensor ,dht11 Is the most used one , In many classes , It is the first choice . Only one... Is needed IO mouth , Temperature and humidity collection can be completed . Share and use here FPGA To complete DHT11 A collection of temperature and humidity demo Share .
You can pay attention to WeChat official account if you need complete code. FPGA The journey reply DHT11-FPGA obtain

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Two . Temperature and humidity collection

1. The data transmission process includes the following three parts : Acquisition start , Collect data , End of collection .
2. Acquisition start ,FPGA Pull down the data line , Then release , wait for dht11 Respond to .
3. The collected data is 40bit, Respectively ( High to the end ) 8bit Humidity integer ,8bit Humidity decimal places ,8bit Temperature integer ,8bit Temperature decimal places ,8bit The checksum .
4. The verification sum is the sum of temperature and humidity data 8 position .
5. End of collection , Pull down the data cable from the machine .

The data transmission process is relatively easy , Let's elaborate on the continuity of each part .

(1) Acquisition start

1. FPGA Pull down the data cable at least 18ms, recommend 20ms. Release the bus , Wait for the slave to pull down the bus response . After the response is received , The bus is released . The detailed process is as follows .

(2) Collect data

The data shows ： data 0 ： 50us Low level plus 26us~28us High level of . data 1：50us Low level plus 70us High level of

(3) End of collection

Pull down the bus from the slave 50us.

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The time here can be adjusted according to the actual test results . It's important , Otherwise, the collected data may be inaccurate .

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3、 ... and . Code implementation

You can pay attention to WeChat official account if you need complete code. FPGA The journey reply DHT11-FPGA obtain
Here, a three-stage state machine is used to realize , It's more convenient . It can be easily determined by the transmission process that the entire acquisition process is determined by four states .
The following is the acquisition results obtained by the logic analyzer , You can see in the S_OVER in , A complete data has been collected .
By calculation 42 + 05 + 1D + 03 = 67 ( Hexadecimal ) It can be determined that the collected data is completely correct .

module DTH11(
	input		clk,
	input		rst,
	inout		dht11,
	input		dht11_req,			// Data collection request 
	output	dht11_down,			// Data acquisition complete 
	output[7:0]	tempH,			// Temperature data integer 
	output[7:0]	tempL,			// Temperature data decimal 
	output[7:0]	humidityH,		// Temperature data integer 
	output[7:0]	humidityL		// Temperature data decimal 
);

localparam	S_IDLE		=	'd0;	// Idle state 
localparam	S_START		=	'd1;	// Start collecting data 
localparam	S_DATA		=	'd2;	// Receive the collected data 
localparam	S_OVER		=	'd3;	// Data acquisition complete 

State transition process

1. S_START： When the collection request comes , Enter the start state
2. S_DATA：step Express start The four parts of the State , Pull down the main engine , Start and end of slave response and start of data transmission .
3. S_OVER：step Indicates the number of received data , When the received data is 40 When , Get into S_OVER state
4. S_IDLE : timeCount Lower the time to end and enter S_IDLE state .

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begin
	case(state)
	S_IDLE:
		if(dht11_req == 1'b1)
			next_state <= S_START;
		else
			next_state <= S_IDLE;
	S_START:
		if(step == 'd4)
			next_state <= S_DATA;
		else
			next_state <= S_START;
	S_DATA:
		if(step == 'd40)
			next_state <= S_OVER;
		else
			next_state <= S_DATA;
	S_OVER:
		if(timeCount == Time50us)
			next_state <= S_IDLE;
		else
			next_state <= S_OVER;
	default:
		next_state <= S_IDLE;
	endcase
end