CODEWITHSUNDEEP
arduino
Maor
Maor

Reputation: 97

DHT11 - difference between integral and decimal data

I am using DHT11 sensor in my arduino uno . the data format sent by the sensor is the following : 8bit integral RH data + 8bit decimal RH data + 8bit integral T data + 8bit decimal T data + 8bit check sum.

the code I used is :

//KY015 DHT11 Temperature and humidity sensor 
   int DHpin = 8;
   byte dat [5];
   byte read_data () {
   byte data;
  for (int i = 0; i < 8; i ++) {
if (digitalRead (DHpin) == LOW) {
  while (digitalRead (DHpin) == LOW); // wait for 50us
  delayMicroseconds (30); // determine the duration of the high level to determine the data is '0 'or '1'
  if (digitalRead (DHpin) == HIGH)
    data |= (1 << (7-i)); // high front and low in the post
  while (digitalRead (DHpin) == HIGH); // data '1 ', wait for the next one receiver
 }
  }
   return data;
  }

  void start_test () {
    digitalWrite (DHpin, LOW); // bus down, send start signal
    delay (30); // delay greater than 18ms, so DHT11 start signal can be detected

    digitalWrite (DHpin, HIGH);
    delayMicroseconds (40); // Wait for DHT11 response

    pinMode (DHpin, INPUT);
    while (digitalRead (DHpin) == HIGH);
    delayMicroseconds (80); // DHT11 response, pulled the bus 80us
    if (digitalRead (DHpin) == LOW);
    delayMicroseconds (80); // DHT11 80us after the bus pulled to start sending data

    for (int i = 0; i < 4; i ++) // receive temperature and humidity data, the parity bit is not considered
dat[i] = read_data ();

    pinMode (DHpin, OUTPUT);
    digitalWrite (DHpin, HIGH); // send data once after releasing the bus, wait for the host to open the next Start signal
  }

  void setup () {
    Serial.begin (9600);
    pinMode (DHpin, OUTPUT);
  }

  void loop () {
    start_test ();
    Serial.print ("Current humdity =");
    Serial.print (dat [0], DEC); // display the humidity-bit integer;
    Serial.print ('.');
    Serial.print (dat [1], DEC); // display the humidity decimal places;
    Serial.println ('%');
    Serial.print ("Current temperature =");
    Serial.print (dat [2], DEC); // display the temperature of integer bits;
    Serial.print ('.');
    Serial.print (dat [3], DEC); // display the temperature of decimal places;
    Serial.println ('C');
    delay (700);
  }

This code probably wont be my final one but I'm trying to get a grasp about what is going on with the data of the sensor. I dont understand why the integear data and the decimal data both are printed as DEC nor do I understand why there is a "." there . this code is taken from the wiki page of the sensor . also I am alwayes getting 0 in the decmial data section of both humidity and temp .

Upvotes: 2

Views: 3370

Answers (1)

Sreekanth
Sreekanth

Reputation: 66

The data conversion is like this For humidity,

Humidity Value = ((float)((integral RH data << 8) + 8bit decimal RH data)/(float)10.0)

For Temperature,

Temperature Value = ((float)((8bit integral T data << 8) + 8bit decimal T data)/(float)10.0)

For example :

8bit integral T data = 0x01 and  8bit decimal T data = 0x32

The real measured temperature value  = ((0x01 << 8) + 0x32) /10
                                     =  (256 + 50 )/10 = 30.6 degree c

Same way for humidity also which will be represented in%. Please note this I did for DHT22 for which the step size(resolution was .1 degree) for DHT11 it seems like 1 degree.

With reference to your code

Serial.print ("Current humdity =");
Serial.print (dat [0], DEC); // display the humidity-bit integer;
Serial.print ('.');
Serial.print (dat [1], DEC); // display the humidity decimal places;
Serial.println ('%');
Serial.print ("Current temperature =");
Serial.print (dat [2], DEC); // display the temperature of integer bits;
Serial.print ('.');
Serial.print (dat [3], DEC); // display the temperature of decimal places;
Serial.println ('C');

I think it won't display the correct value as the conversion is missing.

Upvotes: 1

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