79 lines
2 KiB
C
79 lines
2 KiB
C
#include "dht11.h"
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#include <inttypes.h>
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#include <avr/io.h>
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#include <util/delay.h>
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#include "defines.h"
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int dht11_humidity;
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int dht11_temperature;
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int dht11_read(){
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// Init Timer1 for timekeeping
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TIMSK1=0; // no interrupt
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TCNT1 = 0; // start at 0
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TCCR1A = 0; // nothing to do w timer
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TCCR1B = _BV(CS11); // start w 1us tick
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// BUFFER TO RECEIVE
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uint8_t bits[5];
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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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bitSet(DHT11_DDDR,DHT11_DBIT); //pinMode(pin, OUTPUT);
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bitSet(DHT11_DPORT,DHT11_DBIT); // digitalWrite(pin, HIGH);
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_delay_ms(30);
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bitClear(DHT11_DPORT,DHT11_DBIT); //digitalWrite(pin, LOW);
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_delay_ms(18);
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bitSet(DHT11_DPORT,DHT11_DBIT); // digitalWrite(pin, HIGH);
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_delay_us(20);
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bitClear(DHT11_DDDR,DHT11_DBIT); //pinMode(pin, INPUT);
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bitSet(DHT11_DPORT,DHT11_DBIT);
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// ACKNOWLEDGE or TIMEOUT
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unsigned int loopCnt = 10000;
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while( bitRead(DHT11_DPIN,DHT11_DBIT) == LOW)
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if (loopCnt-- == 0) return DHT11_ERROR_TIMEOUT2;
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loopCnt = 10000;
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while( bitRead(DHT11_DPIN,DHT11_DBIT) == HIGH)
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if (loopCnt-- == 0) return DHT11_ERROR_TIMEOUT2;
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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(bitRead(DHT11_DPIN,DHT11_DBIT) == LOW)
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if (loopCnt-- == 0) return DHT11_ERROR_TIMEOUT;
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unsigned long t = TCNT1;
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loopCnt = 10000;
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while(bitRead(DHT11_DPIN,DHT11_DBIT) == HIGH)
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if (loopCnt-- == 0) return DHT11_ERROR_TIMEOUT;
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unsigned long t2 = TCNT1;
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if ((t2 - 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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dht11_humidity = bits[0];
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dht11_temperature = bits[2];
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uint8_t sum = bits[0] + bits[2];
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if (bits[4] != sum) return DHT11_ERROR_CHECKSUM;
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return DHT11_OK;
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}
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