How to use DHT22 with STM32
UPDATE
If you are not able to get DHT11 or DHT22 values, Here is another method you can use. This one is unified for both the sensors. No setup needed for timer and all. Just select the data pin as output and you are done. you need to select the DHT TYPE in DHT.c
https://controllerstech.com/wp-content/uploads/2020/06/DHT_11_22_DWT.zip
In my last post, I mentioned the use of microseconds delay, check HERE, and this post is the application of that. Today I am going to interface DHT22 with STM32 microcontroller, which utilizes delay in microseconds.
The DHT-22 is a digital-output relative humidity and temperature sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air, and sends out a digital signal on the data pin. You can download the datasheet HERE.
I am not going to waste more time by going into more details, I am sure you already know what this is and that’s why you are here. So let’s jump to the point. If you look at the datasheet, you will find the signal pattern to initialize the sensor as shown in the picture below
INITIALIZATION
Here the black line is the signal from the microcontroller and the white line is the signal from the DHT22. In order to initialize the sensor, we have to pull the data line LOW for at least 1ms, and pull it HIGH for around 20-40 us.
On receiving the start signal, DHT22 will indicate it’s presence by pulling the line low for 80us and than high for 80us.
NOTE:- You might need to connect pull-up resistance to the data line or else DHT22 will not be able to pull it HIGH.
To initialize the sensor, the steps are as follows:-
- Set the pin (data) as output
- Pull the pin low and wait for > 1 ms
- Pull the pin high and wait for 30 us
- Release the pin by setting it as input
DHT22 will now send the response as you can see in the figure above. To check the response, steps are as follows:-
- wait for 40us
- Check if the pin is low, than wait for 80 us. This will totally be a delay of 120 us and the pin should be high now
- Check if the pin is high. If it is, than the response is OK
- Now wait for the pin to go LOW
DATA Transmission
Now DHT22 will send 40 bits of data. Each bit’s transmission begins with low-voltage-level that last 50 us, the following high-voltage-level signal’s length decides whether the bit is “1” or “0”.
- If the length of high-voltage-level is around 26-28 us, the bit is “0”
- And if the length is around 70 us, than the bit is “1”
The 40 bits sent by DHT22 are as follows DATA = 8 bit integral RH data + 8 bit decimal RH data + 8 bit integral T data+8 bit decimal T data + 8 bit checksum
If the data transmission is right, check-sum should be the last 8 bit of “8 bit integral RH data+8 bit decimal RH data+8 bit integral T data+8 bit decimal T data”.
Following are the steps to READ DATA from the sensor
- Wait for the pin to go high
- Wait for 40us. This is because the length of “0” bit is 26-28us, and if the pin is high after 40us, it indicates that the bit is “1”
- write the respective values to the variable
Connection
Some Insight into the CODE
INITIALIZATION
void DHT22_Start (void)
{
Set_Pin_Output(DHT22_PORT, DHT22_PIN); // set the pin as output
HAL_GPIO_WritePin (DHT22_PORT, DHT22_PIN, 0); // pull the pin low
HAL_Delay(1200); // wait for > 1ms
HAL_GPIO_WritePin (DHT22_PORT, DHT22_PIN, 1); // pull the pin high
delay (20); // wait for 30us
Set_Pin_Input(DHT22_PORT, DHT22_PIN); // set as input
}- Set the pin (data) as output
- Pull the pin low and wait for > 1 ms
- set the pin as input for receiving the data
RESPONSE
uint8_t DHT22_Check_Response (void)
{
Set_Pin_Input(DHT22_PORT, DHT22_PIN); // set as input
uint8_t Response = 0;
delay (40); // wait for 40us
if (!(HAL_GPIO_ReadPin (DHT22_PORT, DHT22_PIN))) // if the pin is low
{
delay (80); // wait for 80us
if ((HAL_GPIO_ReadPin (DHT22_PORT, DHT22_PIN))) Response = 1; // if the pin is high, response is ok
else Response = -1;
}
while ((HAL_GPIO_ReadPin (DHT22_PORT, DHT22_PIN))); // wait for the pin to go low
return Response;
}- wait for 40 us
- check if the pin is low, than wait for 80 us. This will totally be a delay of 120 us and the pin should be high now
- Check if the pin is high. If it is, than the response is OK
READ DATA
uint8_t DHT22_Read (void)
{
uint8_t i,j;
for (j=0;j<8;j++)
{
while (!(HAL_GPIO_ReadPin (DHT22_PORT, DHT22_PIN))); // wait for the pin to go high
delay (40); // wait for 40 us
if (!(HAL_GPIO_ReadPin (DHT22_PORT, DHT22_PIN))) // if the pin is low
{
i&= ~(1<<(7-j)); // write 0
}
else i|= (1<<(7-j)); // if the pin is high, write 1
while ((HAL_GPIO_ReadPin (DHT22_PORT, DHT22_PIN))); // wait for the pin to go low
}
return i;
}- Wait for the pin to go high
- Wait for 40 us. This is because the length of “0” bit is 26-28 us and if the pin is high after 40 us, it indicates that the bit is “1”
- write the respective values to the variable
Result
37 Comments. Leave new
Hey man,
You got small bug here in the initialization code (just here on the website, source code in zip file is OK thought).
HAL_Delay(1200); // wait for > 1ms
should be
delay (1200); // wait for > 1ms
Checksum requires fix in the function DHT_GetData below as it is failing.
if (SUM == ( (Rh_byte1 + Rh_byte2 + Temp_byte1 + Temp_byte2) & 0x00FF) ) { #if defined(TYPE_DHT11) DHT_Data->Temperature = Temp_byte1; DHT_Data->Humidity = Rh_byte1; #endif #if defined(TYPE_DHT22) DHT_Data->Temperature = ( ((Temp_byte1 << 8) | Temp_byte2) * 0.1f); DHT_Data->Humidity = ( ((Rh_byte1 << 8) | Rh_byte2) * 0.1f); #endif }Hello,
Where can i found i2c-led.h and .c files?
check the src and inc folders..
I’ve practiced everything you’ve told us. But, while ((HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))); // wait for the pin to go low
in this line, waiting forever, I can not go to next step. What could be the reason ?
The line of code I’m talking about in response function
I have the same problem…..
did you solve the problem
I managed to solve it with the admin. My problem was because i didn’t use 5k ohms pull up and because my stm32 f303k8 had 8MHz system clock. After using internal pull up and setting system clock to 64MHz it worked like a charm.
Unfortunately it did not solve this problem for me. Did anyone solve this problem in another way?
The same problem here… Still no solution?
i created new project and solved this problem. But i did not understand how problem is solved 🙂
i think problem is lcd_init() function. when i added lcd_init function in main funcion, dht22 is not working.
Hi, why you used separate delay function instead of HAL Delay? Any specific reason?
HAL_Delay have the minimum delay of 1 ms on the other hand DHT11 and 22 needs the delays in microseconds. That’s why I used DWT
Thanks for the clarification!
Hi! Thank you for your tuto! For the right checksum you shound do:
if (sum == ((Rh_byte1+Rh_byte2+Temp_byte1+Temp_byte2) & 0xFF))
Best regards
In line No. 78 if ((HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))) check = 1;
Variable “check” is not used anywhrere. Could you explain Why the “check” need?
I personally used “check” for debugging purposes and forgot to remove it.
Thanks for your reply!!
can you tell how to interface ppd42 with stm32
hi please run remote codelearn 433mhz with stm32f103 please help me thanks
hello thanks for the code, i want to read values from dht22 but without using an LCD how could to modify your code to be useful in my case
just use the following code
DHT22_start ();
check_response ();
Rh_byte1 = read_data ();
Rh_byte2 = read_data ();
Temp_byte1 = read_data ();
Temp_byte2 = read_data ();
sum = read_data();
//if (sum == (Rh_byte1+Rh_byte2+Temp_byte1+Temp_byte2))
{
TEMP = ((Temp_byte1<<8)|Temp_byte2); RH = ((Rh_byte1<<8)|Rh_byte2); } No LCD related functions... that's it
thank u, i run it and it works
is it same and works for dht11 module?
DHT11 have a little different timing requirements..
I’ll post a tutorial about it soon
Hello, I just followed your youtube video here.
This code is different with another I2C code,
First your codes on this project are:
void lcd_send_cmd (char cmd)
{
char data_u, data_l;
uint8_t data_t[4];
data_u = cmd&0xf0;
data_l = (cmd<<4)&0xf0;
data_t[0] = data_u|0x04; //en=1, rs=0
data_t[1] = data_u; //en=0, rs=0
data_t[2] = data_l|0x04; //en=1, rs=0
data_t[3] = data_l; //en=0, rs=0
HAL_I2C_Master_Transmit (&hi2c1, 0x4E,(uint8_t *) data_t, 4, 100);
}
void lcd_send_data (char data)
{
char data_u, data_l;
uint8_t data_t[4];
data_u = data&0xf0;
data_l = (data<<4)&0xf0;
data_t[0] = data_u|0x05; //en=1, rs=0
data_t[1] = data_u|0x01; //en=0, rs=0
data_t[2] = data_l|0x05; //en=1, rs=0
data_t[3] = data_l|0x01; //en=0, rs=0
HAL_I2C_Master_Transmit (&hi2c1, 0x4E,(uint8_t *) data_t, 4, 100);
}
But in another project, the lcd_send_cmd and lcd_send_data used different numbers for the data_t[ ] calculation. Why and which one is correct?
void lcd_send_cmd (char cmd)
{
char data_u, data_l;
uint8_t data_t[4];
data_u = (cmd&0xf0);
data_l = ((cmd<<4)&0xf0);
data_t[0] = data_u|0x0C; //en=1, rs=0
data_t[1] = data_u|0x08; //en=0, rs=0
data_t[2] = data_l|0x0C; //en=1, rs=0
data_t[3] = data_l|0x08; //en=0, rs=0
HAL_I2C_Master_Transmit (&hi2c1, SLAVE_ADDRESS_LCD,(uint8_t *) data_t, 4, 100);
}
void lcd_send_data (char data)
{
char data_u, data_l;
uint8_t data_t[4];
data_u = (data&0xf0);
data_l = ((data<<4)&0xf0);
data_t[0] = data_u|0x0D; //en=1, rs=0
data_t[1] = data_u|0x09; //en=0, rs=0
data_t[2] = data_l|0x0D; //en=1, rs=0
data_t[3] = data_l|0x09; //en=0, rs=0
HAL_I2C_Master_Transmit (&hi2c1, SLAVE_ADDRESS_LCD,(uint8_t *) data_t, 4, 100);
}
The down one is a fix for lcd backlight so I recommend you use that.
Thank you for your response.
I have another question:
What commands should I send to turn on/off the backlight? I know P3 is the backlight control pin.
I just can’t figure out a way to change only one bit of the register.
I figured it out myself. Need to read the register first then change P3 bit and write it back.
Do I need to change the Master Transmit address from 0x4E to whatevery my I2C is putting out? For Arduino I needed to use a scanner and check to see what it was and change that over before transmitting? Just wondering because I used everything here for my STM32F4 and it’s not working…thanks.
0x4E is the address of the slave device PCF8574. If you are using any other variant, you need to change the address.
where is dwt_stm32_delay.h/dwt_stm32_delay.c please !
Sorry for that. I uploaded the wrong one.
You can download NOW
Hi, Where are the “dwt_stm32_delay.h/dwt_stm32_delay.c ” and i2c files… Please I need them asap. Many thanks.
Download the code.. They are in src and inc folders