sharif omar / lib_dht22

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Dependents:   Mytemperature_Motion

dht22.cpp@0:e50b1c66ec57, 2019-04-21 (annotated)

Committer:
sharifdeens
Date:
Sun Apr 21 03:29:29 2019 +0000
Revision:
0:e50b1c66ec57
n/a

Who changed what in which revision?

UserRevisionLine numberNew contents of line
sharifdeens 0:e50b1c66ec57 1 /*
sharifdeens 0:e50b1c66ec57 2 * (C) The University of Kent and Simon Cooksey 2015.
sharifdeens 0:e50b1c66ec57 3 */
sharifdeens 0:e50b1c66ec57 4
sharifdeens 0:e50b1c66ec57 5 #include "mbed.h"
sharifdeens 0:e50b1c66ec57 6 #include <inttypes.h>
sharifdeens 0:e50b1c66ec57 7
sharifdeens 0:e50b1c66ec57 8 #include "dht22.h"
sharifdeens 0:e50b1c66ec57 9
sharifdeens 0:e50b1c66ec57 10 /*
sharifdeens 0:e50b1c66ec57 11 * The DHT22 uses a 1 wire interface, sending 1's and 0s by varying the length
sharifdeens 0:e50b1c66ec57 12 * of the HIGH time on the signal pin.
sharifdeens 0:e50b1c66ec57 13 */
sharifdeens 0:e50b1c66ec57 14
sharifdeens 0:e50b1c66ec57 15 /*
sharifdeens 0:e50b1c66ec57 16 * Wait for a rising or falling edge on the sense pin.
sharifdeens 0:e50b1c66ec57 17 *
sharifdeens 0:e50b1c66ec57 18 * Returns: the number of uS elapsed before the transition
sharifdeens 0:e50b1c66ec57 19 */
sharifdeens 0:e50b1c66ec57 20 int DHT22::wait_for_edge(edge_type_t type)
sharifdeens 0:e50b1c66ec57 21 {
sharifdeens 0:e50b1c66ec57 22 dht22_s.input();
sharifdeens 0:e50b1c66ec57 23
sharifdeens 0:e50b1c66ec57 24 // Timing is done by increasing this number, as the Timer class appears to
sharifdeens 0:e50b1c66ec57 25 // be super slow.
sharifdeens 0:e50b1c66ec57 26 int time = 0;
sharifdeens 0:e50b1c66ec57 27 do {
sharifdeens 0:e50b1c66ec57 28 wait_us(2);
sharifdeens 0:e50b1c66ec57 29 time+=2;
sharifdeens 0:e50b1c66ec57 30 } while(dht22_s != (int)type);
sharifdeens 0:e50b1c66ec57 31
sharifdeens 0:e50b1c66ec57 32 // wait for the edge to transition properly
sharifdeens 0:e50b1c66ec57 33 wait_us(2);
sharifdeens 0:e50b1c66ec57 34 return time;
sharifdeens 0:e50b1c66ec57 35 }
sharifdeens 0:e50b1c66ec57 36
sharifdeens 0:e50b1c66ec57 37 /*
sharifdeens 0:e50b1c66ec57 38 * Send a start bit to the DHT22
sharifdeens 0:e50b1c66ec57 39 */
sharifdeens 0:e50b1c66ec57 40 void DHT22::send_start()
sharifdeens 0:e50b1c66ec57 41 {
sharifdeens 0:e50b1c66ec57 42 dht22_s.output();
sharifdeens 0:e50b1c66ec57 43 dht22_s = 0;
sharifdeens 0:e50b1c66ec57 44 wait_us(DHT22_START_BIT_TIME);
sharifdeens 0:e50b1c66ec57 45 dht22_s = 1;
sharifdeens 0:e50b1c66ec57 46 dht22_s.input();
sharifdeens 0:e50b1c66ec57 47 }
sharifdeens 0:e50b1c66ec57 48
sharifdeens 0:e50b1c66ec57 49 /*
sharifdeens 0:e50b1c66ec57 50 * Wait for the DHT22 to send the start bit ACK, after this we can read data.
sharifdeens 0:e50b1c66ec57 51 */
sharifdeens 0:e50b1c66ec57 52 void DHT22::await_start_response()
sharifdeens 0:e50b1c66ec57 53 {
sharifdeens 0:e50b1c66ec57 54 dht22_s.input();
sharifdeens 0:e50b1c66ec57 55 wait_for_edge(EDGE_TYPE_FALLING); // 20-40 uS
sharifdeens 0:e50b1c66ec57 56 wait_for_edge(EDGE_TYPE_RISING); // 80 uS
sharifdeens 0:e50b1c66ec57 57 wait_for_edge(EDGE_TYPE_FALLING); // 80 uS
sharifdeens 0:e50b1c66ec57 58 }
sharifdeens 0:e50b1c66ec57 59
sharifdeens 0:e50b1c66ec57 60 /*
sharifdeens 0:e50b1c66ec57 61 * Reads 16 bits of data from the DHT22
sharifdeens 0:e50b1c66ec57 62 *
sharifdeens 0:e50b1c66ec57 63 * Returns: the signed value read. dht22_t.
sharifdeens 0:e50b1c66ec57 64 * NB. the DHT22 uses a sign bit to do -ve and positive, but this is
sharifdeens 0:e50b1c66ec57 65 * incompatible with signed numbers in C, so the conversion is done here.
sharifdeens 0:e50b1c66ec57 66 */
sharifdeens 0:e50b1c66ec57 67 int16_t DHT22::read_word()
sharifdeens 0:e50b1c66ec57 68 {
sharifdeens 0:e50b1c66ec57 69 dht22_s.input();
sharifdeens 0:e50b1c66ec57 70 int32_t duration;
sharifdeens 0:e50b1c66ec57 71 int16_t word = 0x00;
sharifdeens 0:e50b1c66ec57 72 for(char bit = 0; bit < 16; bit++)
sharifdeens 0:e50b1c66ec57 73 {
sharifdeens 0:e50b1c66ec57 74 /* /-----------\
sharifdeens 0:e50b1c66ec57 75 * / duration \ 50us
sharifdeens 0:e50b1c66ec57 76 * ----/ \-------
sharifdeens 0:e50b1c66ec57 77 */
sharifdeens 0:e50b1c66ec57 78 wait_for_edge(EDGE_TYPE_RISING);
sharifdeens 0:e50b1c66ec57 79 duration = wait_for_edge(EDGE_TYPE_FALLING);
sharifdeens 0:e50b1c66ec57 80
sharifdeens 0:e50b1c66ec57 81 if(duration > DHT22_SIGNAL_HIGH_LOW_BOUNDARY)
sharifdeens 0:e50b1c66ec57 82 {
sharifdeens 0:e50b1c66ec57 83 word |= (1 << 15-bit);
sharifdeens 0:e50b1c66ec57 84 }
sharifdeens 0:e50b1c66ec57 85 else
sharifdeens 0:e50b1c66ec57 86 {
sharifdeens 0:e50b1c66ec57 87 word |= (0 << 15-bit);
sharifdeens 0:e50b1c66ec57 88 }
sharifdeens 0:e50b1c66ec57 89 }
sharifdeens 0:e50b1c66ec57 90 if(word & 0x8000)
sharifdeens 0:e50b1c66ec57 91 return 1 - (word ^ 0x8000);
sharifdeens 0:e50b1c66ec57 92 return word;
sharifdeens 0:e50b1c66ec57 93 }
sharifdeens 0:e50b1c66ec57 94
sharifdeens 0:e50b1c66ec57 95 /*
sharifdeens 0:e50b1c66ec57 96 * Reads 8 bits of data from the DHT22
sharifdeens 0:e50b1c66ec57 97 *
sharifdeens 0:e50b1c66ec57 98 * Returns: the unsigned checksum value read. dht22_t.
sharifdeens 0:e50b1c66ec57 99 */
sharifdeens 0:e50b1c66ec57 100 uint8_t DHT22::read_checksum()
sharifdeens 0:e50b1c66ec57 101 {
sharifdeens 0:e50b1c66ec57 102 dht22_s.input();
sharifdeens 0:e50b1c66ec57 103 uint32_t duration;
sharifdeens 0:e50b1c66ec57 104 uint8_t word;
sharifdeens 0:e50b1c66ec57 105 for(char bit = 0; bit < sizeof(uint8_t)*8; bit++)
sharifdeens 0:e50b1c66ec57 106 {
sharifdeens 0:e50b1c66ec57 107 /* /-----------\
sharifdeens 0:e50b1c66ec57 108 * / duration \ 50us
sharifdeens 0:e50b1c66ec57 109 * ----/ \-------
sharifdeens 0:e50b1c66ec57 110 */
sharifdeens 0:e50b1c66ec57 111 wait_for_edge(EDGE_TYPE_RISING);
sharifdeens 0:e50b1c66ec57 112 duration = wait_for_edge(EDGE_TYPE_FALLING);
sharifdeens 0:e50b1c66ec57 113
sharifdeens 0:e50b1c66ec57 114 if(duration > DHT22_SIGNAL_HIGH_LOW_BOUNDARY)
sharifdeens 0:e50b1c66ec57 115 {
sharifdeens 0:e50b1c66ec57 116 word |= (1 << 7-bit);
sharifdeens 0:e50b1c66ec57 117 }
sharifdeens 0:e50b1c66ec57 118 else
sharifdeens 0:e50b1c66ec57 119 {
sharifdeens 0:e50b1c66ec57 120 word |= (0 << 7-bit);
sharifdeens 0:e50b1c66ec57 121 }
sharifdeens 0:e50b1c66ec57 122 }
sharifdeens 0:e50b1c66ec57 123 return word;
sharifdeens 0:e50b1c66ec57 124 }
sharifdeens 0:e50b1c66ec57 125
sharifdeens 0:e50b1c66ec57 126 /*
sharifdeens 0:e50b1c66ec57 127 * Reads a packet of DHT22 data.
sharifdeens 0:e50b1c66ec57 128 *
sharifdeens 0:e50b1c66ec57 129 * Param data: the packet to fill.
sharifdeens 0:e50b1c66ec57 130 */
sharifdeens 0:e50b1c66ec57 131 void DHT22::read(DHT22_data_t * data)
sharifdeens 0:e50b1c66ec57 132 {
sharifdeens 0:e50b1c66ec57 133 // Send start bits
sharifdeens 0:e50b1c66ec57 134 send_start();
sharifdeens 0:e50b1c66ec57 135
sharifdeens 0:e50b1c66ec57 136 // Wait for device to respond
sharifdeens 0:e50b1c66ec57 137 await_start_response();
sharifdeens 0:e50b1c66ec57 138
sharifdeens 0:e50b1c66ec57 139 // Read data bits (16+16)
sharifdeens 0:e50b1c66ec57 140 int16_t humidity = read_word();
sharifdeens 0:e50b1c66ec57 141 int16_t temp = read_word();
sharifdeens 0:e50b1c66ec57 142
sharifdeens 0:e50b1c66ec57 143 // Read checksum (8)
sharifdeens 0:e50b1c66ec57 144 uint8_t checksum = read_checksum();
sharifdeens 0:e50b1c66ec57 145
sharifdeens 0:e50b1c66ec57 146 data->humidity = (humidity);
sharifdeens 0:e50b1c66ec57 147 data->temp = (temp);
sharifdeens 0:e50b1c66ec57 148 data->checksum = checksum;
sharifdeens 0:e50b1c66ec57 149 }