using DHT22 sensor without dht lib

Haider92 · August 26, 2015, 7:04am

hi

im trying to use dht22 sensor and connecting it to arduino uno without using dht lib

the code for sensor

#include "DHT.h"
#define DHTPIN 2     // what pin we're connected to
#define DHTTYPE DHT22   // DHT 22  (AM2302)
DHT dht(DHTPIN, DHTTYPE);


void setup() {
  Serial.begin(9600); 
  Serial.println("DHTxx test!");
  dht.begin();
}

void loop() {

  delay(2000);


  float h = dht.readHumidity();

  float t = dht.readTemperature();

  float f = dht.readTemperature(true);
  
  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  float hi = dht.computeHeatIndex(f, h);

  Serial.print("Humidity: "); 
  Serial.print(h);
  Serial.print(" %\t");
  Serial.print("Temperature: "); 
  Serial.print(t);
  Serial.print(" *C ");
  Serial.print(f);
  Serial.print(" *F\t");
  Serial.print("Heat index: ");
  Serial.print(hi);
  Serial.println(" *F");
}

is there anyone write full code for this sensor without using dht lib
because i have parallax propeller micro controller and i want to connect dht22 sensor with it
but i need to understand how sensor code work to rewrite code for propeller MCU

Kind Regards,

robtillaart · August 26, 2015, 7:57pm

I wrote a DHT lib - Arduino/libraries/DHTstable at master · RobTillaart/Arduino · GitHub -
which works on different processors, see - Arduino Playground - DHTLib

does that count?

Haider92 · August 27, 2015, 6:21am

robtillaart what i want is code without using #include dht.h
i want to rewrite the same code for P8X32A Propeller QuickStart (Rev.B)

Haider92 · August 27, 2015, 6:50am

i find this code
http://www.electrodragon.com/w/index.php?title=DHT11#Demo_code_1

both of demo code doesn't work?

i connect dht22 sensor to Arduino Uno via digital pin 2
also i test my connection with DHT code and lib and it's work fine
is there any modification can we do for anyone of these two demo code to make it work with DHT22

Haider92 · August 27, 2015, 11:26am

any post!

i make some change for code but it's not working

#define dht11_pin 2 //Analog port 0 on Arduino Uno
//#define dht11_pin 54 //Analog port 0 on Arduino Mega2560
 
byte read_dht11_dat()
{
  byte i = 0;
  byte result=0;
  for(i=0; i< 8; i++)
  {
    while (!digitalRead(dht11_pin));
    delayMicroseconds(30);
    if (digitalRead(dht11_pin) != 0 )
      bitSet(result, 7-i);
    while (digitalRead(dht11_pin));
  }
  return result;
}
 
 
void setup()
{
  pinMode(dht11_pin, OUTPUT);
  digitalWrite(dht11_pin, HIGH);
  Serial.begin(9600);
  Serial.println("Ready");
}
 
void loop()    
{
  byte dht11_dat[5];   
  byte dht11_in;
  byte i;// start condition
 
  digitalWrite(dht11_pin, HIGH);
  delay(250);
  digitalWrite(dht11_pin, LOW);
  delay(20);
  digitalWrite(dht11_pin, HIGH);
  delayMicroseconds(40); 
  pinMode(dht11_pin, INPUT);    
 
  if (digitalRead(dht11_pin))
  {
    Serial.println("dht11 start condition 1 not met"); // wait for DHT response signal: LOW
    delay(1000);
    return;
  }
  delayMicroseconds(1);
  if (!digitalRead(dht11_pin))
  {
    Serial.println("dht11 start condition 2 not met");  //wair for second response signal:HIGH
    return;
  }
 
  delayMicroseconds(1);// now ready for data reception
  for (i=0; i<5; i++)
  {  dht11_dat[i] = read_dht11_dat();}  //recieved 40 bits data. Details are described in datasheet
 
  pinMode(dht11_pin, OUTPUT);
  digitalWrite(dht11_pin, HIGH);
  byte dht11_check_sum = dht11_dat[0]+dht11_dat[2];// check check_sum
  if(dht11_dat[4]!= dht11_check_sum)
  {
    Serial.println("DHT11 checksum error");
  }
  Serial.print("Current humdity = ");
  Serial.print(dht11_dat[0], DEC);
  Serial.print("%  ");
  Serial.print("temperature = ");
  Serial.print(dht11_dat[2], DEC);
  Serial.println("C  ");
  delay(2000); //fresh time
}

Haider92 · August 27, 2015, 12:12pm

also this one didn't work, it's show fake temp 32C

#define dht11_pin 2 //Analog port 0 on Arduino Uno
//#define dht11_pin 54 //Analog port 0 on Arduino Mega2560

  uint8_t laststate = HIGH;
  uint8_t counter = 0;
  uint8_t j = 0, i;
uint8_t data[6];
 float f;
 
byte read_dht11_dat()
{
  byte i = 0;
  byte result=0;
  for(i=0; i< 8; i++)
  {
    while (!digitalRead(dht11_pin));
    delayMicroseconds(30);
    if (digitalRead(dht11_pin) != 0 )
      bitSet(result, 7-i);
    while (digitalRead(dht11_pin));
  }
  return result;
}
 
 
void setup()
{
  pinMode(dht11_pin, OUTPUT);
  digitalWrite(dht11_pin, HIGH);
  Serial.begin(9600);
  Serial.println("Ready");
}
 
void loop()    
{
  byte dht11_dat[5];   
  byte dht11_in;
  byte i;// start condition
 
  digitalWrite(dht11_pin, HIGH);
  delay(250);
  digitalWrite(dht11_pin, LOW);
  delay(20);
  digitalWrite(dht11_pin, HIGH);
  delayMicroseconds(40); 
  pinMode(dht11_pin, INPUT);    
  
 data[0] = data[1] = data[2] = data[3] = data[4] = 0;

  for ( i=0; i< 80; i++) {
    counter = 0;
    while (digitalRead(dht11_pin) == laststate) {
      counter++;
      delayMicroseconds(1);
      if (counter == 255) {
        break;
      }
    }
    laststate = digitalRead(dht11_pin);

    if (counter == 255) break;

    // ignore first 3 transitions
    if ((i >= 4) && (i%2 == 0)) {
      // shove each bit into the storage bytes
      data[j/8] <<= 1;
      if (counter > 6)
        data[j/8] |= 1;
      j++;
    }

  }

 f = data[2] & 0x7F;
      f *= 256;
      f += data[3];
      f /= 10;
      if (data[1] & 0x80)
  f *= -1;
      
 f = f * 9 / 5 + 32;
Serial.print("temperature = ");
Serial.print(f);

  delay(2000); //fresh time
}

robtillaart · August 27, 2015, 3:20pm

At what clock speed do you run that processor?
What is the granularity of delayMicroSeconds() on that board?
On an UNO @16MHZ it is 4 micros...

I've run on an UNO successful @8MHz and with dedicated code 4Mhz worked reasonably but not perfect.

Haider92 · August 27, 2015, 4:45pm

i have Arduino UNO chine clone i think it 16 MHZ

robtillaart · August 27, 2015, 6:06pm

You could start with

copying my library code (.cpp) into your sketch
strip the class frame from it
define the class private vars as sketch global vars
call the now standalone functions
have a beer¹ because it works

¹Or another favorit beverage

Haider92 · August 27, 2015, 7:16pm

robtillaart:
You could start with

copying my library code (.cpp) into your sketch

strip the class frame from it

define the class private vars as sketch global vars

call the now standalone functions

have a beer¹ because it works

¹Or another favorit beverage

i do that with this code

#define dht11_pin 2 //Analog port 0 on Arduino Uno
//#define dht11_pin 54 //Analog port 0 on Arduino Mega2560

  uint8_t laststate = HIGH;
  uint8_t counter = 0;
  uint8_t j = 0, i;
uint8_t data[6];
 float f;
 
byte read_dht11_dat()
{
  byte i = 0;
  byte result=0;
  for(i=0; i< 8; i++)
  {
    while (!digitalRead(dht11_pin));
    delayMicroseconds(30);
    if (digitalRead(dht11_pin) != 0 )
      bitSet(result, 7-i);
    while (digitalRead(dht11_pin));
  }
  return result;
}
 
 
void setup()
{
  pinMode(dht11_pin, OUTPUT);
  digitalWrite(dht11_pin, HIGH);
  Serial.begin(9600);
  Serial.println("Ready");
}
 
void loop()   
{
  byte dht11_dat[5];   
  byte dht11_in;
  byte i;// start condition
 
  digitalWrite(dht11_pin, HIGH);
  delay(250);
  digitalWrite(dht11_pin, LOW);
  delay(20);
  digitalWrite(dht11_pin, HIGH);
  delayMicroseconds(40);
  pinMode(dht11_pin, INPUT);   
 
 data[0] = data[1] = data[2] = data[3] = data[4] = 0;

  for ( i=0; i< 80; i++) {
    counter = 0;
    while (digitalRead(dht11_pin) == laststate) {
      counter++;
      delayMicroseconds(1);
      if (counter == 255) {
        break;
      }
    }
    laststate = digitalRead(dht11_pin);

    if (counter == 255) break;

    // ignore first 3 transitions
    if ((i >= 4) && (i%2 == 0)) {
      // shove each bit into the storage bytes
      data[j/8] <<= 1;
      if (counter > 6)
        data[j/8] |= 1;
      j++;
    }

  }

 f = data[2] & 0x7F;
      f *= 256;
      f += data[3];
      f /= 10;
      if (data[1] & 0x80)
  f *= -1;
     
 f = f * 9 / 5 + 32;
Serial.print("temperature = ");
Serial.print(f);

  delay(2000); //fresh time
}

and optimize it to show only temperature in C and its not work

robtillaart · August 27, 2015, 8:29pm

Did you read the datasheet to learn how the protocol/handshake looks like?

Do you use a pull-up resistor?

Haider92 · August 27, 2015, 8:56pm

yes i use pull up resistor also i use your lib and code and my connection work fine
but i want to write sketch for this sensor without using dht lib (put the class needed inside the sketch)

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