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### Topic: Checksum Error in DHT11 (Read 5096 times)previous topic - next topic

#### kukuso

##### Nov 30, 2012, 04:23 pmLast Edit: Nov 30, 2012, 04:27 pm by kukuso Reason: 1
Hi!!!

I'm testing DHT11 sensor with the code I saw in this page:

http://arduino.cc/playground/Main/DHT11Lib

And it's impossible always the same problem "Checksum Error". I've tried with other codes and the same problem always happens.

I've checked elctrical parts, ports... I use Arduino One with Ethernet Shield.

Somebody can I help me?

In advance, thank you very much.

#### robtillaart

#1
##### Nov 30, 2012, 06:02 pm

2) have you tried without Ethernet shield => minimizing your code, or use sample code of the lib

Note the delay time between 2 samples is 2 seconds for DHT11
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#### kukuso

#2
##### Dec 03, 2012, 11:38 am
OK, this is the code

//
//   FILE:  dht11_test1.pde
// PURPOSE: DHT11 library test sketch for Arduino
//

//Celsius to Fahrenheit conversion
double Fahrenheit(double celsius)
{
return 1.8 * celsius + 32;
}

//Celsius to Kelvin conversion
double Kelvin(double celsius)
{
return celsius + 273.15;
}

// dewPoint function NOAA
// reference: http://wahiduddin.net/calc/density_algorithms.htm
double dewPoint(double celsius, double humidity)
{
double A0= 373.15/(273.15 + celsius);
double SUM = -7.90298 * (A0-1);
SUM += 5.02808 * log10(A0);
SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ;
SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
SUM += log10(1013.246);
double VP = pow(10, SUM-3) * humidity;
double T = log(VP/0.61078);   // temp var
return (241.88 * T) / (17.558-T);
}

// delta max = 0.6544 wrt dewPoint()
// 5x faster than dewPoint()
// reference: http://en.wikipedia.org/wiki/Dew_point
double dewPointFast(double celsius, double humidity)
{
double a = 17.271;
double b = 237.7;
double temp = (a * celsius) / (b + celsius) + log(humidity/100);
double Td = (b * temp) / (a - temp);
return Td;
}

#include <dht11.h>

dht11 DHT11;

#define DHT11PIN 2

void setup()
{
Serial.begin(115200);
Serial.println("DHT11 TEST PROGRAM ");
Serial.print("LIBRARY VERSION: ");
Serial.println(DHT11LIB_VERSION);
Serial.println();
}

void loop()
{
Serial.println("\n");

switch (chk)
{
case DHTLIB_OK:
Serial.println("OK");
break;
case DHTLIB_ERROR_CHECKSUM:
Serial.println("Checksum error");
break;
case DHTLIB_ERROR_TIMEOUT:
Serial.println("Time out error");
break;
default:
Serial.println("Unknown error");
break;
}

Serial.print("Humidity (%): ");
Serial.println((float)DHT11.humidity, 2);

Serial.print("Temperature (oC): ");
Serial.println((float)DHT11.temperature, 2);

Serial.print("Temperature (oF): ");
Serial.println(Fahrenheit(DHT11.temperature), 2);

Serial.print("Temperature (K): ");
Serial.println(Kelvin(DHT11.temperature), 2);

Serial.print("Dew Point (oC): ");
Serial.println(dewPoint(DHT11.temperature, DHT11.humidity));

Serial.print("Dew PointFast (oC): ");
Serial.println(dewPointFast(DHT11.temperature, DHT11.humidity));

delay(2000);
}
//
// END OF FILE
//

I have tried without ethernet and nothing.

Sometimes appears Timeout error and other times Checksum error.

#### kukuso

#3
##### Dec 04, 2012, 12:42 pm
Today I checked with other DHT11 and it runs correctly so maybe it was the PCB or own sensor.

Thank you very much!

#### robtillaart

#4
##### Dec 04, 2012, 07:42 pm

you're welcome.

Please use the code tags next time when posting code - it is the # button just above the smileys.

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

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