Eric Fossum / Mbed 2 deprecated DHT11

A minimal library for the DHT11.

Dependencies:   mbed

Dependents:   EXP10_DHT11_LCD Sushil_MODSERIAL Core1000_SmartFarm idd_summer17_hw3_evey_jenny_seiyoung ... more

Dht11.cpp@0:c1da310d3e8a, 2015-02-15 (annotated)

Committer:
fossum_13
Date:
Sun Feb 15 02:09:00 2015 +0000
Revision:
0:c1da310d3e8a
Child:
1:5da6f6de3e42
Initial version

Who changed what in which revision?

UserRevisionLine numberNew contents of line
fossum_13 0:c1da310d3e8a 1 #include "Dht11.h"
fossum_13 0:c1da310d3e8a 2
fossum_13 0:c1da310d3e8a 3 Dht11::Dht11(PinName 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 0:c1da310d3e8a 8 }
fossum_13 0:c1da310d3e8a 9
fossum_13 0:c1da310d3e8a 10 // Return values:
fossum_13 0:c1da310d3e8a 11 // DHTLIB_OK
fossum_13 0:c1da310d3e8a 12 // DHTLIB_ERROR_CHECKSUM
fossum_13 0:c1da310d3e8a 13 // DHTLIB_ERROR_TIMEOUT
fossum_13 0:c1da310d3e8a 14 int Dht11::read()
fossum_13 0:c1da310d3e8a 15 {
fossum_13 0:c1da310d3e8a 16 // BUFFER TO RECEIVE
fossum_13 0:c1da310d3e8a 17 uint8_t bits[5];
fossum_13 0:c1da310d3e8a 18 uint8_t cnt = 7;
fossum_13 0:c1da310d3e8a 19 uint8_t idx = 0;
fossum_13 0:c1da310d3e8a 20
fossum_13 0:c1da310d3e8a 21 // EMPTY BUFFER
fossum_13 0:c1da310d3e8a 22 for (int i=0; i< 5; i++) bits[i] = 0;
fossum_13 0:c1da310d3e8a 23
fossum_13 0:c1da310d3e8a 24 // Verify sensor settled after boot
fossum_13 0:c1da310d3e8a 25 while(_timer.read_ms() < 1500) {}
fossum_13 0:c1da310d3e8a 26 _timer.stop();
fossum_13 0:c1da310d3e8a 27
fossum_13 0:c1da310d3e8a 28 // Notify it we are ready to read
fossum_13 0:c1da310d3e8a 29 _pin.output();
fossum_13 0:c1da310d3e8a 30 _pin = 0;
fossum_13 0:c1da310d3e8a 31 wait_ms(18);
fossum_13 0:c1da310d3e8a 32 _pin = 1;
fossum_13 0:c1da310d3e8a 33 wait_us(40);
fossum_13 0:c1da310d3e8a 34 _pin.input();
fossum_13 0:c1da310d3e8a 35
fossum_13 0:c1da310d3e8a 36 // ACKNOWLEDGE or TIMEOUT
fossum_13 0:c1da310d3e8a 37 unsigned int loopCnt = 10000;
fossum_13 0:c1da310d3e8a 38 while(_pin == 0)
fossum_13 0:c1da310d3e8a 39 if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
fossum_13 0:c1da310d3e8a 40
fossum_13 0:c1da310d3e8a 41 loopCnt = 10000;
fossum_13 0:c1da310d3e8a 42 while(_pin == 1)
fossum_13 0:c1da310d3e8a 43 if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
fossum_13 0:c1da310d3e8a 44
fossum_13 0:c1da310d3e8a 45 // READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT
fossum_13 0:c1da310d3e8a 46 for (int i=0; i<40; i++)
fossum_13 0:c1da310d3e8a 47 {
fossum_13 0:c1da310d3e8a 48 loopCnt = 10000;
fossum_13 0:c1da310d3e8a 49 while(_pin == 0)
fossum_13 0:c1da310d3e8a 50 if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
fossum_13 0:c1da310d3e8a 51
fossum_13 0:c1da310d3e8a 52 //unsigned long t = micros();
fossum_13 0:c1da310d3e8a 53 Timer t;
fossum_13 0:c1da310d3e8a 54 t. start();
fossum_13 0:c1da310d3e8a 55
fossum_13 0:c1da310d3e8a 56 loopCnt = 10000;
fossum_13 0:c1da310d3e8a 57 while(_pin == 1)
fossum_13 0:c1da310d3e8a 58 if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
fossum_13 0:c1da310d3e8a 59
fossum_13 0:c1da310d3e8a 60 if (t.read_us() > 40) bits[idx] |= (1 << cnt);
fossum_13 0:c1da310d3e8a 61 if (cnt == 0) // next byte?
fossum_13 0:c1da310d3e8a 62 {
fossum_13 0:c1da310d3e8a 63 cnt = 7; // restart at MSB
fossum_13 0:c1da310d3e8a 64 idx++; // next byte!
fossum_13 0:c1da310d3e8a 65 }
fossum_13 0:c1da310d3e8a 66 else cnt--;
fossum_13 0:c1da310d3e8a 67 }
fossum_13 0:c1da310d3e8a 68
fossum_13 0:c1da310d3e8a 69 // WRITE TO RIGHT VARS
fossum_13 0:c1da310d3e8a 70 // as bits[1] and bits[3] are allways zero they are omitted in formulas.
fossum_13 0:c1da310d3e8a 71 _humidity = bits[0];
fossum_13 0:c1da310d3e8a 72 _temperature = bits[2];
fossum_13 0:c1da310d3e8a 73
fossum_13 0:c1da310d3e8a 74 uint8_t sum = bits[0] + bits[2];
fossum_13 0:c1da310d3e8a 75
fossum_13 0:c1da310d3e8a 76 if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;
fossum_13 0:c1da310d3e8a 77 return DHTLIB_OK;
fossum_13 0:c1da310d3e8a 78 }
fossum_13 0:c1da310d3e8a 79
fossum_13 0:c1da310d3e8a 80 int Dht11::temperature() {
fossum_13 0:c1da310d3e8a 81 return(_temperature);
fossum_13 0:c1da310d3e8a 82 }
fossum_13 0:c1da310d3e8a 83
fossum_13 0:c1da310d3e8a 84 int Dht11::humidity() {
fossum_13 0:c1da310d3e8a 85 return(_humidity);
fossum_13 0:c1da310d3e8a 86 }