106 lines
2.8 KiB
C
106 lines
2.8 KiB
C
/*
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* dht22.c:
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* Simple test program to test the wiringPi functions
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* Based on the existing dht11.c
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* Amended by technion@lolware.net
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*/
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#include <wiringPi.h>
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#include "dht22.h"
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <sys/types.h>
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#include <unistd.h>
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#define MAXTIMINGS 85
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static int DHTPIN = 7;
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static int dht22_dat[5] = {0,0,0,0,0};
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static uint8_t sizecvt(const int read)
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{
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/* digitalRead() and friends from wiringpi are defined as returning a value
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*< 256. However, they are returned as int() types. This is a safety function */
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if (read > 255 || read < 0)
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{
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printf("Invalid data from wiringPi library\n");
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exit(EXIT_FAILURE);
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}
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return (uint8_t)read;
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}
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static int read_dht22_dat(sensor *s)
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{
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uint8_t laststate = HIGH;
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uint8_t counter = 0;
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uint8_t j = 0, i;
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DHTPIN = s->pin;
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dht22_dat[0] = dht22_dat[1] = dht22_dat[2] = dht22_dat[3] = dht22_dat[4] = 0;
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// pull pin down for 18 milliseconds
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pinMode(DHTPIN, OUTPUT);
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digitalWrite(DHTPIN, HIGH);
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delay(10);
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digitalWrite(DHTPIN, LOW);
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delay(18);
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// then pull it up for 40 microseconds
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digitalWrite(DHTPIN, HIGH);
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delayMicroseconds(40);
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// prepare to read the pin
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pinMode(DHTPIN, INPUT);
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// detect change and read data
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for ( i=0; i< MAXTIMINGS; i++) {
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counter = 0;
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while (sizecvt(digitalRead(DHTPIN)) == laststate) {
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counter++;
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delayMicroseconds(1);
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if (counter == 255) {
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break;
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}
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}
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laststate = sizecvt(digitalRead(DHTPIN));
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if (counter == 255) break;
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// ignore first 3 transitions
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if ((i >= 4) && (i%2 == 0)) {
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// shove each bit into the storage bytes
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dht22_dat[j/8] <<= 1;
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if (counter > 16)
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dht22_dat[j/8] |= 1;
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j++;
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}
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}
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// check we read 40 bits (8bit x 5 ) + verify checksum in the last byte
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// print it out if data is good
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if ((j >= 40) &&
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(dht22_dat[4] == ((dht22_dat[0] + dht22_dat[1] + dht22_dat[2] + dht22_dat[3]) & 0xFF)) ) {
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float t, h;
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h = (float)dht22_dat[0] * 256 + (float)dht22_dat[1];
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h /= 10;
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t = (float)(dht22_dat[2] & 0x7F)* 256 + (float)dht22_dat[3];
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t /= 10.0;
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if ((dht22_dat[2] & 0x80) != 0) t *= -1;
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//printf("Humidity = %.2f %% Temperature = %.2f *C \n", h, t );
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s->humidity = h;
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s->temperature = t;
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return 1;
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} else {
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//printf("Data not good, skip\n");
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return 0;
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}
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}
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void getData(sensor *s) {
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int tries = 100;
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while (read_dht22_dat(s) == 0 && tries--) {
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delay(1000);
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}
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}
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