interfacing DHT22 sensor with stm32f411re

[Reva1605]

I am trying to interface DHT22 sensor with STM32F411RE board. When initially I interfaced I was able to see data (i.e., Temp and Humidity) I am giving 3.3v power supply, data pin connected to PA0 ground and set clock frequency to 50MHZ using Internal oscillator. But when now I am trying to check values, I am not able to get values I haven't change anything in code still I am facing this issue. The code is stuck in while loop of DHT22_response function where it is waiting for pin to be low. I have attached coding file please can anyone help me regarding this??

[STackPointer64]

Hello @Reva1605,

Have you tried connecting a pull-up resistor to the data line? Without it, the DHT11 may not be able to pull the line HIGH.

Best regards,

[Reva1605]

Yes tried connecting pull-up resistor of value 4.7k still not working

[STackPointer64]

So, to understand correctly, you created a project and added the functions to interface with the DHT22 sensor. Initially, it worked, but after rebuilding and testing the project again, it got stuck in the DHT22_response function? Have you tried supplying 5V to the sensor or using a different GPIO pin instead of the wakeup pin PA0?

[Andrew Neil]

Welcome to the forum.

Please see How to write your question to maximize your chances to find a solution for best results.

In particular, please describe:

• What board you are using
• Show schematic of how the DHT22 is connected
• Show some good, clear photos of your setup
• Describe what testing/investigation/debugging you've done so far;
  eg, have you looked at the signal line on an oscilloscope?

[Reva1605]

I have tried supplying 5v to sensor. I haven't tried using different GPIO pin I will try that once.

[Reva1605]

As mentioned, I am using STM32F411RE board and interfacing DHT22 sensor. So previously I was testing dht22 sensor with 3.3v power supply I was giving me correct values of humidity and temperature but now when I am trying get values it is stuck in DHT22_response () .
About setup it is just simple connection between stm32 board and dht22 sensor.

[KnarfB]

The following worked here with a DHT11:

int main(void)
{
    __HAL_RCC_GPIOA_CLK_ENABLE();

    GPIO_InitTypeDef GPIO_InitStruct;

    GPIO_InitStruct.Pin   = DHT11_DAT_PIN;
    GPIO_InitStruct.Mode  = GPIO_MODE_OUTPUT_OD;
    GPIO_InitStruct.Pull  = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    HAL_GPIO_Init(DHT11_DAT_PORT, &GPIO_InitStruct);

    HAL_GPIO_WritePin( DHT11_DAT_PORT, DHT11_DAT_PIN, GPIO_PIN_SET);
    delay_us(1000*1000); 	// wait after power on

    for(;;) {
        HAL_GPIO_WritePin( DHT11_DAT_PORT, DHT11_DAT_PIN, GPIO_PIN_RESET);
        delay_us(20*1000);		// wait >18ms
        HAL_GPIO_WritePin( DHT11_DAT_PORT, DHT11_DAT_PIN, GPIO_PIN_SET);
        ReadDHT11();
        delay_us(2*1000*1000); 	// wait 2s for next reading
    }
}

 Differences:

- the pin is never pushed high

- the pin is read while in output mode  

- give it time to start-up after power-on

hth

KnarfB

[Reva1605]

I am using DHT22 so will it work with my sensor?

[KnarfB]

The translated english data sheets show pretty much the same diagrams, copied from the chinese originals. There are some differences in electrical and environmental conditions: Overview | DHT11, DHT22 and AM2302 Sensors | Adafruit Learning System

As theres are quite old parts, there are dozends of tutorials around...

hth

KnarfB