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Class for reading DHT22 values on a Spark Core
#define MAXTIMINGS 85
#define cli noInterrupts
#define sei interrupts
#define DHT11 11
#define DHT22 22
#define DHT21 21
#define AM2301 21
#define NAN 999999
class DHT {
private:
uint8_t data[6];
uint8_t _pin, _type, _count;
bool read(void);
unsigned long _lastreadtime;
bool firstreading;
public:
DHT(uint8_t pin, uint8_t type, uint8_t count=6);
void begin(void);
float readTemperature(bool S=false);
float convertCtoF(float);
float readHumidity(void);
};
DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
_pin = pin;
_type = type;
_count = count;
firstreading = true;
}
void DHT::begin(void) {
// set up the pins!
pinMode(_pin, INPUT);
digitalWrite(_pin, HIGH);
_lastreadtime = 0;
}
//boolean S == Scale. True == Farenheit; False == Celcius
float DHT::readTemperature(bool S) {
float _f;
if (read()) {
switch (_type) {
case DHT11:
_f = data[2];
if(S)
_f = convertCtoF(_f);
return _f;
case DHT22:
case DHT21:
_f = data[2] & 0x7F;
_f *= 256;
_f += data[3];
_f /= 10;
if (data[2] & 0x80)
_f *= -1;
if(S)
_f = convertCtoF(_f);
return _f;
}
}
return NAN;
}
float DHT::convertCtoF(float c) {
return c * 9 / 5 + 32;
}
float DHT::readHumidity(void) {
float _f;
if (read()) {
switch (_type) {
case DHT11:
_f = data[0];
return _f;
case DHT22:
case DHT21:
_f = data[0];
_f *= 256;
_f += data[1];
_f /= 10;
return _f;
}
}
return NAN;
}
bool DHT::read(void) {
uint8_t laststate = HIGH;
uint8_t counter = 0;
uint8_t j = 0, i;
unsigned long currenttime;
// pull the pin high and wait 250 milliseconds
digitalWrite(_pin, HIGH);
delay(250);
currenttime = millis();
if (currenttime < _lastreadtime) {
// ie there was a rollover
_lastreadtime = 0;
}
if (!firstreading && ((currenttime - _lastreadtime) < 2000)) {
//delay(2000 - (currenttime - _lastreadtime));
return true; // return last correct measurement
}
firstreading = false;
Serial.print("Currtime: "); Serial.print(currenttime);
Serial.print(" Lasttime: "); Serial.print(_lastreadtime);
_lastreadtime = millis();
data[0] = data[1] = data[2] = data[3] = data[4] = 0;
// now pull it low for ~20 milliseconds
pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
delay(20);
cli();
digitalWrite(_pin, HIGH);
delayMicroseconds(40);
pinMode(_pin, INPUT);
// read in timings
for ( i=0; i< MAXTIMINGS; i++) {
counter = 0;
while (digitalRead(_pin) == laststate) {
counter++;
delayMicroseconds(1);
if (counter == 255)
break;
}
laststate = digitalRead(_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 > _count)
data[j/8] |= 1;
j++;
}
}
sei();
// check we read 40 bits and that the checksum matches
if ((j >= 40) && (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)))
return true;
return false;
}
#define DHTPIN D2 // Digital pin D2
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);
float h; // humidity
float t; // temperature
int f = 0; // failed?
void setup() {
dht.begin();
}
void loop() {
f = 0;
h = dht.readHumidity();
t = dht.readTemperature();
if (t==NAN || h==NAN)
f = 1;
else
f = 0;
}

thank you!

Great job! Thanks!

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