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Class for reading DHT22 values on a Spark Core
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#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; | |
} |
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