102 lines
2.5 KiB
C++
102 lines
2.5 KiB
C++
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//
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// FILE: dht11.cpp
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// VERSION: 0.4.1
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// PURPOSE: DHT11 Temperature & Humidity Sensor library for Arduino
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// LICENSE: GPL v3 (http://www.gnu.org/licenses/gpl.html)
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//
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// DATASHEET: http://www.micro4you.com/files/sensor/DHT11.pdf
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//
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// HISTORY:
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// George Hadjikyriacou - Original version (??)
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// Mod by SimKard - Version 0.2 (24/11/2010)
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// Mod by Rob Tillaart - Version 0.3 (28/03/2011)
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// + added comments
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// + removed all non DHT11 specific code
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// + added references
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// Mod by Rob Tillaart - Version 0.4 (17/03/2012)
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// + added 1.0 support
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// Mod by Rob Tillaart - Version 0.4.1 (19/05/2012)
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// + added error codes
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//
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#include "dht11.h"
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// Return values:
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// DHTLIB_OK
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// DHTLIB_ERROR_CHECKSUM
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// DHTLIB_ERROR_TIMEOUT
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int dht11::read(int pin)
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{
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// BUFFER TO RECEIVE
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uint8_t bits[5]={0,0,0,0,0};
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uint8_t cnt = 7;
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uint8_t idx = 0;
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// EMPTY BUFFER
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for (int i=0; i< 5; i++) bits[i] = 0;
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// REQUEST SAMPLE
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pinMode(pin, OUTPUT);
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digitalWrite(pin, LOW);
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delay(20);
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digitalWrite(pin, HIGH);
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delayMicroseconds(40);
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pinMode(pin, INPUT);
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// ACKNOWLEDGE or TIMEOUT
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unsigned int loopCnt = 80;
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while(digitalRead(pin) == LOW)
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{
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delayMicroseconds(1);
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if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
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}
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loopCnt = 80;
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while(digitalRead(pin) == HIGH)
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{
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delayMicroseconds(1);
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if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
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}
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// READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT
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for (int i=0; i<40; i++)
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{
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loopCnt = 10000;
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while(digitalRead(pin) == LOW)
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if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
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unsigned long t = micros();
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loopCnt = 10000;
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while(digitalRead(pin) == HIGH)
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if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
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if ((micros() - t) > 40) bits[idx] |= (1 << cnt);
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if (cnt == 0) // next byte?
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{
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cnt = 7; // restart at MSB
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idx++; // next byte!
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}
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else cnt--;
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}
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// WRITE TO RIGHT VARS
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// as bits[1] and bits[3] are allways zero they are omitted in formulas.
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humidity = bits[0];
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temperature = bits[2];
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byt0=bits[0];
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byt1=bits[1];
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byt2=bits[2];
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byt3=bits[3];
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byt4=bits[4];
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uint8_t sum = bits[0] + bits[1]+bits[2]+bits[3];
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if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;
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return DHTLIB_OK;
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}
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//
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// END OF FILE
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//
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