DHT humidity / temperature simulator 0.1.01 (DHT22 and compatible)

Development Libraries
1

To be able to test my DHT library in an easy way I decided to write a DHT simulator a few weeks ago.
This weekend I found some time to read through the specs and wrote the sketch below

I used two potmeters:
one to simulate humidity 0.0 ... 100.0 %
one to simulate temperature -20.0 ... 184.6 C

You can use this code (small changes) to create a virtual DHT22 sensor based upon any other temperature sensor - analog or digital e.g. LM35, thermocouple, DHT11 + DS18B20 etc. Even non-temperature sensors - e.g. flex-sensor and a bi-metal; pressure-sensor or volume sensor - and some physics formula's can be used to create virtual temperature sensors.

The code is tested on an UNO and a Duemilanove 16 MHZ - connect datapin & GND - and has run for several hours now without flaws.

I am especially interested if anyone can confirms it works on a ATTINYxx (for making virtual DHT22's with e.g analog sensors)

Use the code at your own risk, have fun, and as always remarks and ideas are welcome!

//
//    FILE: DHT_simulator.ino
//  AUTHOR: Rob Tillaart
// VERSION: 0.1.01
// PURPOSE: simulator to test DHT lib
//    DATE: 2014-06-14
//     URL:
//
// Released to the public domain
//

// TODO
// - robustness
// - timeout loops

const int dataPin = 5;
byte b[5];

void setup() 
{
  Serial.begin(115200);
  Serial.print("Start ");
  Serial.println(__FILE__);

  pinMode(dataPin, INPUT_PULLUP);
}

void loop() 
{
  // T = -200 .. 1800
  analogRead(A2);
  int T = analogRead(A2) * 2 - 200; 

  // H = 0 .. 1000
  analogRead(A0);
  int H = analogRead(A0);
  if (H > 1000) 
  {
    H = 1000;                
  }
  //  Serial.print(H);
  //  Serial.print("\t");
  //  Serial.println(T);

  // WAKE UP SIGNAL DETECTED
  if (digitalRead(dataPin) == LOW)     
  {
    uint32_t start = micros();
    // wait until signal goes high 
    // todo timeout on blocking loop
    while (digitalRead(dataPin) == LOW)
    {
      if (micros() - start > 1500) return;  
    }
    if (micros() - start > 500) // serious request...
    {
      DHTsend(H, T);

      Serial.print(H);
      Serial.print("\t");
      Serial.println(T);
    }
  }
}


void DHTsend(int H, int T)
{
  pinMode(dataPin, OUTPUT); 
  // SEND ACK
  digitalWrite(dataPin, LOW);
  delayMicroseconds(80);                  // 80 us
  digitalWrite(dataPin, HIGH);
  delayMicroseconds(80);                  // 80 us

  // PREPARE DATA
  b[0] = H / 256;
  b[1] = H & 255;

  b[2] = 0;
  if (T < 0) 
  {
    T = -T;
    b[2] = 0x80;
  }

  b[2] |= T / 256;
  b[3] = T & 255;
  // CRC
  b[4] = b[0] + b[1] + b[2] + b[3];

  // SEND DATA
  for (int i = 0; i < 5; i++)
  {
    DHTsendbyte(b[i]);
  }

  // END OF TRANSMISSION SIGNAL
  digitalWrite(dataPin, LOW);
  delayMicroseconds(50);                  // 50 us
  pinMode(dataPin, INPUT_PULLUP);

  // DEBUG 
  //  for (int i = 0; i < 5; i++)
  //  {
  //    Serial.print(b[i]);
  //    Serial.print(" ");
  //  }
  //  Serial.println();
}

// timing manual tuned
void DHTsendbyte(byte b)
{
  byte mask = 128;
  for(int i = 0; i < 8; i++)
  {
    digitalWrite(dataPin, LOW);
    delayMicroseconds(45);                // 50 us
    digitalWrite(dataPin, HIGH);
    if (b & mask) delayMicroseconds(60);  // 70 us
    else delayMicroseconds(24);           // 26 us
    mask >>= 1;
  }
}

to be continued.

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