Why is my code acting like that?

Using Arduino Programming Questions
1

Hello :slight_smile:

I have an small problem with a part of my code:

Here is code which doesn't work as it should:

#include <Wire.h>
#include <DS3231.h>
#include <DHT22.h>

DS3231 RTC;
DHT22 DHT22_0( 2 );
DHT22 DHT22_1( 3 );

void DHT22_PrintData( DHT22 device );

unsigned long lastReadTime;
unsigned long currentTime;

void setup () 
{
    Serial.begin(57600);
    
    Wire.begin();
    
    RTC.begin();
    //DateTime dt(__DATE__, __TIME__);
    //RTC.adjust(dt);
    
    //Small delay needed for the DHT22 startup correctly
    delay( 2000 );

    lastReadTime = millis();
}

void loop () 
{
  currentTime = millis();
  if (currentTime - lastReadTime >= 1000)
  {
    DateTime now = RTC.now();
    char str[120];
    sprintf( str, "%s %02d %s %04d %02d:%02d:%02d - %.1f°C",
    now.dayName(), now.date(), now.monthName(), now.year(), now.hour(), now.minute(), now.second(), RTC.getTemperature());
    Serial.println(str);


    Serial.print("DHT22_0: ");
    DHT22_PrintData( DHT22_0 );
    Serial.print("DHT22_1: ");
    DHT22_PrintData( DHT22_1 );


    Serial.println( );
    lastReadTime = currentTime;
  }
}

void DHT22_PrintData( DHT22 device )
{
  switch( device.readData() )
  {
    case DHT_ERROR_NONE:
      char buf[128];
      sprintf(buf, "%.1f°C %.1f%% RH", device.getTemperatureC(), device.getHumidity() );
      Serial.println(buf);
      break;
    case DHT_ERROR_CHECKSUM:
      Serial.print("check sum error ");
      Serial.print( device.getTemperatureC() );
      Serial.print("C ");
      Serial.print( device.getHumidity() );
      Serial.println("%");
      break;
    case DHT_BUS_HUNG:
      Serial.println("BUS Hung ");
      break;
    case DHT_ERROR_NOT_PRESENT:
      Serial.println("Not Present ");
      break;
    case DHT_ERROR_ACK_TOO_LONG:
      Serial.println("ACK time out ");
      break;
    case DHT_ERROR_SYNC_TIMEOUT:
      Serial.println("Sync Timeout ");
      break;
    case DHT_ERROR_DATA_TIMEOUT:
      Serial.println("Data Timeout ");
      break;
    case DHT_ERROR_TOOQUICK:
      Serial.println("Polled to quick ");
      break;
  }
}

Here is the output of this program:

Monday 29 April 2013 01:37:47 - 21.3°C
DHT22_0: 21.8°C 48.9% RH
DHT22_1: 21.9°C 49.1% RH

Monday 29 April 2013 01:37:48 - 21.3°C
DHT22_0: 21.8°C 48.7% RH
DHT22_1: 21.9°C 49.1% RH

Monday 29 April 2013 01:37:49 - 21.3°C
DHT22_0: 21.8°C 48.9% RH
DHT22_1: 21.8°C 49.0% RH

Monday 29 April 2013 01:37:50 - 21.3°C
DHT22_0: 21.8°C 48.9% RH
DHT22_1: 21.8°C 49.0% RH

Monday 29 April 2013 01:37:51 - 21.3°C
DHT22_0: 21.8°C 48.9% RH
DHT22_1: 21.9°C 49.1% RH

It looks like it is correct, and while it works perfectly fine to me, in theory it should report an error "Polled too quick" once every 2 seconds, since there is this part in the library's readData function:

if(currentTime - _lastReadTime < 2000)
{
  // Caller needs to wait 2 seconds between each call to readData
  return DHT_ERROR_TOOQUICK;
}

(And it is said in the DHT22 datasheet, polling should be > 1.7 seconds )

Now if I try this code (the same thing but without my function "PrintData") then everything work as should:

#include <Wire.h>
#include <DS3231.h>
#include <DHT22.h>

DS3231 RTC;
DHT22 DHT22_0( 2 );
DHT22 DHT22_1( 3 );

unsigned long lastReadTime;
unsigned long currentTime;

void setup () 
{
    Serial.begin(57600);
    
    Wire.begin();
    
    RTC.begin();
    //DateTime dt(__DATE__, __TIME__);
    //RTC.adjust(dt);
    
    //Small delay needed for the DHT22 startup correctly
    delay( 2000 );

    lastReadTime = millis();
}

void loop () 
{
  currentTime = millis();
  if (currentTime - lastReadTime >= 1000)
  {
    DateTime now = RTC.now();
    char str[120];
    sprintf( str, "%s %02d %s %04d %02d:%02d:%02d - %.1f°C",
    now.dayName(), now.date(), now.monthName(), now.year(), now.hour(), now.minute(), now.second(), RTC.getTemperature());
    Serial.println(str);


    switch( DHT22_0.readData() )
    {
      case DHT_ERROR_NONE:
        char buf[128];
        sprintf(buf, "DHT22_0: %.1f°C %.1f%% RH",
          DHT22_0.getTemperatureC(),DHT22_0.getHumidity());
        Serial.println(buf);
        break;
      case DHT_ERROR_CHECKSUM:
        Serial.print("check sum error ");
        Serial.print(DHT22_0.getTemperatureC());
        Serial.print("C ");
        Serial.print(DHT22_0.getHumidity());
        Serial.println("%");
        break;
      case DHT_BUS_HUNG:
        Serial.println("BUS Hung ");
        break;
      case DHT_ERROR_NOT_PRESENT:
        Serial.println("Not Present ");
        break;
      case DHT_ERROR_ACK_TOO_LONG:
        Serial.println("ACK time out ");
        break;
      case DHT_ERROR_SYNC_TIMEOUT:
        Serial.println("Sync Timeout ");
        break;
      case DHT_ERROR_DATA_TIMEOUT:
        Serial.println("Data Timeout ");
        break;
      case DHT_ERROR_TOOQUICK:
        Serial.println("Polled to quick ");
        break;
    }
    
    switch( DHT22_1.readData() )
    {
      case DHT_ERROR_NONE:
        char buf[128];
        sprintf(buf, "DHT22_1: %.1f°C %.1f%% RH",
          DHT22_1.getTemperatureC(),DHT22_1.getHumidity());
        Serial.println(buf);
        break;
      case DHT_ERROR_CHECKSUM:
        Serial.print("check sum error ");
        Serial.print(DHT22_1.getTemperatureC());
        Serial.print("C ");
        Serial.print(DHT22_1.getHumidity());
        Serial.println("%");
        break;
      case DHT_BUS_HUNG:
        Serial.println("BUS Hung ");
        break;
      case DHT_ERROR_NOT_PRESENT:
        Serial.println("Not Present ");
        break;
      case DHT_ERROR_ACK_TOO_LONG:
        Serial.println("ACK time out ");
        break;
      case DHT_ERROR_SYNC_TIMEOUT:
        Serial.println("Sync Timeout ");
        break;
      case DHT_ERROR_DATA_TIMEOUT:
        Serial.println("Data Timeout ");
        break;
      case DHT_ERROR_TOOQUICK:
        Serial.println("Polled to quick ");
        break;
    }


    Serial.println( );
    lastReadTime = currentTime;
  }
}

Monday 29 April 2013 01:44:36 - 21.0°C
DHT22_0: 21.7°C 48.1% RH
DHT22_1: 21.8°C 49.2% RH

Monday 29 April 2013 01:44:37 - 21.0°C
Polled to quick 
Polled to quick 

Monday 29 April 2013 01:44:38 - 21.0°C
DHT22_0: 21.7°C 48.1% RH
DHT22_1: 21.7°C 49.2% RH

Monday 29 April 2013 01:44:39 - 21.0°C
Polled to quick 
Polled to quick

It's like if in the first code, my device.readData() always return 0 (DHT_ERROR_NONE)... but the device's temp and humidity were still updated!

Can you find what is the problem?

2

I am not familiar with the DHT22 library, but should you be passing the DHT22 by value as a parameter to your read function? This is a guess, but I think the function will be creating its own instantiation of a DHT22 when you do that, which it probably not what you want.

Perhaps pass a pointer to your DHT22 object instead:

...
DHT22_PrintData( &DHT22_0 );
...
void DHT22_PrintData( DHT22* device)
{
  switch ( device->readData() )
...
3

Ah, of course, that worked :slight_smile:

That was just a test, actually I did it differently (without so much error checking) but, thank you anyway Prof Chaos :slight_smile:

4