Amit Gandhi / DHT22_2

A minimal library for the DHT11.

Fork of DHT11 by Eric Fossum

Dht22.cpp@2:983fdd709bf7, 2017-11-09 (annotated)

Committer:
amithy
Date:
Thu Nov 09 22:14:56 2017 +0000
Revision:
2:983fdd709bf7
Parent:
Dht11.cpp@1:5da6f6de3e42 
test export

Who changed what in which revision?

UserRevisionLine numberNew contents of line
amithy 2:983fdd709bf7 1 #include "Dht22.h"
fossum_13 0:c1da310d3e8a 2
amithy 2:983fdd709bf7 3 Dht22::Dht22(PinName const &p) : _pin(p) {
fossum_13 0:c1da310d3e8a 4 // Set creation time so we can make
fossum_13 0:c1da310d3e8a 5 // sure we pause at least 1 second for
fossum_13 0:c1da310d3e8a 6 // startup.
fossum_13 0:c1da310d3e8a 7 _timer.start();
fossum_13 1:5da6f6de3e42 8
fossum_13 1:5da6f6de3e42 9 _temperature = 0;
fossum_13 1:5da6f6de3e42 10 _humidity = 0;
fossum_13 0:c1da310d3e8a 11 }
fossum_13 0:c1da310d3e8a 12
amithy 2:983fdd709bf7 13 int Dht22::read()
fossum_13 0:c1da310d3e8a 14 {
fossum_13 0:c1da310d3e8a 15 // BUFFER TO RECEIVE
fossum_13 0:c1da310d3e8a 16 uint8_t bits[5];
fossum_13 0:c1da310d3e8a 17 uint8_t cnt = 7;
fossum_13 0:c1da310d3e8a 18 uint8_t idx = 0;
fossum_13 0:c1da310d3e8a 19
fossum_13 0:c1da310d3e8a 20 // EMPTY BUFFER
fossum_13 0:c1da310d3e8a 21 for (int i=0; i< 5; i++) bits[i] = 0;
fossum_13 0:c1da310d3e8a 22
fossum_13 0:c1da310d3e8a 23 // Verify sensor settled after boot
fossum_13 0:c1da310d3e8a 24 while(_timer.read_ms() < 1500) {}
fossum_13 0:c1da310d3e8a 25 _timer.stop();
fossum_13 0:c1da310d3e8a 26
fossum_13 0:c1da310d3e8a 27 // Notify it we are ready to read
fossum_13 0:c1da310d3e8a 28 _pin.output();
fossum_13 0:c1da310d3e8a 29 _pin = 0;
fossum_13 0:c1da310d3e8a 30 wait_ms(18);
fossum_13 0:c1da310d3e8a 31 _pin = 1;
fossum_13 0:c1da310d3e8a 32 wait_us(40);
fossum_13 0:c1da310d3e8a 33 _pin.input();
fossum_13 0:c1da310d3e8a 34
fossum_13 0:c1da310d3e8a 35 // ACKNOWLEDGE or TIMEOUT
fossum_13 0:c1da310d3e8a 36 unsigned int loopCnt = 10000;
fossum_13 0:c1da310d3e8a 37 while(_pin == 0)
fossum_13 0:c1da310d3e8a 38 if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
fossum_13 0:c1da310d3e8a 39
fossum_13 0:c1da310d3e8a 40 loopCnt = 10000;
fossum_13 0:c1da310d3e8a 41 while(_pin == 1)
fossum_13 0:c1da310d3e8a 42 if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
fossum_13 0:c1da310d3e8a 43
fossum_13 0:c1da310d3e8a 44 // READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT
fossum_13 0:c1da310d3e8a 45 for (int i=0; i<40; i++)
fossum_13 0:c1da310d3e8a 46 {
fossum_13 0:c1da310d3e8a 47 loopCnt = 10000;
fossum_13 0:c1da310d3e8a 48 while(_pin == 0)
fossum_13 0:c1da310d3e8a 49 if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
fossum_13 0:c1da310d3e8a 50
fossum_13 0:c1da310d3e8a 51 //unsigned long t = micros();
fossum_13 0:c1da310d3e8a 52 Timer t;
fossum_13 0:c1da310d3e8a 53 t. start();
fossum_13 0:c1da310d3e8a 54
fossum_13 0:c1da310d3e8a 55 loopCnt = 10000;
fossum_13 0:c1da310d3e8a 56 while(_pin == 1)
fossum_13 0:c1da310d3e8a 57 if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
fossum_13 0:c1da310d3e8a 58
fossum_13 0:c1da310d3e8a 59 if (t.read_us() > 40) bits[idx] |= (1 << cnt);
fossum_13 0:c1da310d3e8a 60 if (cnt == 0) // next byte?
fossum_13 0:c1da310d3e8a 61 {
fossum_13 0:c1da310d3e8a 62 cnt = 7; // restart at MSB
fossum_13 0:c1da310d3e8a 63 idx++; // next byte!
fossum_13 0:c1da310d3e8a 64 }
fossum_13 0:c1da310d3e8a 65 else cnt--;
fossum_13 0:c1da310d3e8a 66 }
fossum_13 0:c1da310d3e8a 67
amithy 2:983fdd709bf7 68 // // WRITE TO RIGHT VARS - DHT22
amithy 2:983fdd709bf7 69 // // as bits[1] and bits[3] are allways zero they are omitted in formulas.
amithy 2:983fdd709bf7 70 // _humidity = bits[0];
amithy 2:983fdd709bf7 71 // _temperature = bits[2];
amithy 2:983fdd709bf7 72 //
amithy 2:983fdd709bf7 73 // uint8_t sum = bits[0] + bits[2];
amithy 2:983fdd709bf7 74 //
amithy 2:983fdd709bf7 75 // if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;
amithy 2:983fdd709bf7 76
amithy 2:983fdd709bf7 77
amithy 2:983fdd709bf7 78 uint8_t dht22_check_sum;
amithy 2:983fdd709bf7 79 dht22_check_sum = bits[0] + bits[1] + bits[2] + bits[3];
amithy 2:983fdd709bf7 80 //printf("dht22 check sum: %d",dht22_check_sum);
amithy 2:983fdd709bf7 81 dht22_check_sum= dht22_check_sum%256;
amithy 2:983fdd709bf7 82 //printf("dht22 check sum: %d",dht22_check_sum);
amithy 2:983fdd709bf7 83
amithy 2:983fdd709bf7 84 if (dht22_check_sum == bits[4]) {
amithy 2:983fdd709bf7 85 _humidity = bits[0]*256 + bits[1];
amithy 2:983fdd709bf7 86
amithy 2:983fdd709bf7 87 _temperature = bits[2]*256 + bits[3];
amithy 2:983fdd709bf7 88 //printf("all good \n");
amithy 2:983fdd709bf7 89 return DHTLIB_OK;
amithy 2:983fdd709bf7 90 }
amithy 2:983fdd709bf7 91 return DHTLIB_ERROR_CHECKSUM;
fossum_13 0:c1da310d3e8a 92 }
fossum_13 0:c1da310d3e8a 93
amithy 2:983fdd709bf7 94 float Dht22::getFahrenheit() {
fossum_13 1:5da6f6de3e42 95 return((_temperature * 1.8) + 32);
fossum_13 1:5da6f6de3e42 96 }
fossum_13 1:5da6f6de3e42 97
amithy 2:983fdd709bf7 98 int Dht22::getCelsius() {
fossum_13 0:c1da310d3e8a 99 return(_temperature);
fossum_13 0:c1da310d3e8a 100 }
fossum_13 0:c1da310d3e8a 101
amithy 2:983fdd709bf7 102 int Dht22::getHumidity() {
fossum_13 0:c1da310d3e8a 103 return(_humidity);
fossum_13 0:c1da310d3e8a 104 }