tinyDHT/dht11.c at master · StefKode/tinyDHT · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
/*
 * The Tinusaur Project
 *
 * TinuDHT - Tinusaur DHT11 Library
 *
 * @created: 2014-07-08
 * @author: Neven Boyanov
 *
 * Source code available at: https://bitbucket.org/tinusaur/tinudht
 *
 */

// ----------------------------------------------------------------------------

#include <stdlib.h>
#include <avr/io.h>
#include <util/delay.h>

#include "dht11.h"

// ----------------------------------------------------------------------------

#define TINUDHT_RCV_TIMEOUT 255
#define TINUDHT_RCV_DELAY  5
#define TINUDHT_RCV_LENGTH 5

// ----------------------------------------------------------------------------

uint8_t tinudht_read(TinuDHT *ptinudht, uint8_t dht_pin)
{
	uint8_t data[5];

	// Empty the buffer
	for (uint8_t i=0; i< 5; i++) data[i] = 0;	// Another way to empty the data buffer.

	// Send request
	DDRB |= (1 << dht_pin);	// Set port as output
	PORTB &= ~(1 << dht_pin);	// Set to 0
	_delay_ms(18);	// Wait 18 ms
	PORTB |= (1 << dht_pin);	// Set to 1
	_delay_us(40);	// Wait 40 us

	// Receive response
	DDRB &= ~(1 << dht_pin);	// Set port as input
//		PORTB |= (1 << dht_pin);	// Set to 1, optional pull-up.

	uint8_t timeout;

    ptinudht->dbg = 0;
	// Acknowledge
	timeout = TINUDHT_RCV_TIMEOUT;
	while(bit_is_clear(PINB, dht_pin))	// Wait for 1
		if (timeout-- == 0)
			return TINUDHT_ERROR_TIMEOUT;

    //ptinudht->dbg++;
	timeout = TINUDHT_RCV_TIMEOUT;
	while(bit_is_set(PINB, dht_pin))	// Wait for 0
		if (timeout-- == 0)
			return TINUDHT_ERROR_TIMEOUT;

	uint8_t bit_index = 7;
	uint8_t byte_index = 0;
	// READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT
	for (uint8_t i = 0; i < 40; i++)
	{
        ptinudht->dbg++;

		// Wait for start
		timeout = TINUDHT_RCV_TIMEOUT;
		while(bit_is_clear(PINB, dht_pin))	// Wait for 1
			if (timeout-- == 0)
				return TINUDHT_ERROR_TIMEOUT;

        ptinudht->dbg++;

		// Determine the bit value
		uint8_t len = 0;
		while(bit_is_set(PINB, dht_pin)) {	// Wait for 0
			_delay_us(TINUDHT_RCV_DELAY);
			if (len++ == TINUDHT_RCV_TIMEOUT)
				return TINUDHT_ERROR_TIMEOUT;
			}

		if (len >= TINUDHT_RCV_LENGTH) data[byte_index] |= (1 << bit_index);

		// Experiments:
		// delay =    0,     len = 3..6 - 7:unstable
		// delay =  1us,     len = 3..5
		// delay =  2us,     len = 3..5
		// delay =  5us,     len = 3..5
		// delay = 10us,     len = 2..4
		// delay = 15us,     len = 2..3
		// delay = 20us,     len = 2    - 3:unstable
		// delay =  9..29us, len = 2

		// NOTE: The values of TINUDHT_RCV_DELAY and TINUDHT_RCV_LENGTH
		//       may need to be adjusted if the F_CPU changes.

		if (bit_index == 0)	// next byte?
		{
			bit_index = 7;	// restart at MSB
			byte_index++;	// next byte!
		}
		else bit_index--;

        //ptinudht->dbg -= 2;
	}

    ptinudht->dbg++;
	// DEBUGGING
	// DEBUGGING_STRING("DH:");
	// DEBUGGING_NUMDECP(data[0]);
	// DEBUGGING_NUMDECP(data[1]);
	// DEBUGGING_STRING("\n\r");
	// DEBUGGING_STRING("DT:");
	// DEBUGGING_NUMDECP(data[2]);
	// DEBUGGING_NUMDECP(data[3]);
	// DEBUGGING_STRING("\n\r");

	uint8_t checksum = data[0] + data[2];	// TODO: Fix this, does not work in border cases.
	if (data[4] != checksum) return TINUDHT_ERROR_CHECKSUM;

    ptinudht->dbg++;
	// DEBUGGING
	// DEBUGGING_STRING("CS:");
	// DEBUGGING_NUMDECP(data[4]);
	// DEBUGGING_NUMDECP(checksum);
	// DEBUGGING_STRING("\n\r");

	// On DHT11 data[1],data[3] are always zero so not used.
	ptinudht->humidity = data[0] + 5;
	ptinudht->temperature = data[2] + 2;

	return TINUDHT_OK;
}