dht22, main, makefile

dht22.c

@@ -0,0 +1,105 @@
+/*
+ *      dht22.c:
+ *	Simple test program to test the wiringPi functions
+ *	Based on the existing dht11.c
+ *	Amended by technion@lolware.net
+ */
+
+#include <wiringPi.h>
+#include "dht22.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+
+#define MAXTIMINGS 85
+static int DHTPIN = 7;
+static int dht22_dat[5] = {0,0,0,0,0};
+
+static uint8_t sizecvt(const int read)
+{
+    /* digitalRead() and friends from wiringpi are defined as returning a value
+     *< 256. However, they are returned as int() types. This is a safety function */
+    
+    if (read > 255 || read < 0)
+    {
+        printf("Invalid data from wiringPi library\n");
+        exit(EXIT_FAILURE);
+    }
+    return (uint8_t)read;
+}
+
+static int read_dht22_dat(int pin, sensor *s)
+{
+    uint8_t laststate = HIGH;
+    uint8_t counter = 0;
+    uint8_t j = 0, i;
+    DHTPIN = pin;
+    
+    dht22_dat[0] = dht22_dat[1] = dht22_dat[2] = dht22_dat[3] = dht22_dat[4] = 0;
+    
+    // pull pin down for 18 milliseconds
+    pinMode(DHTPIN, OUTPUT);
+    digitalWrite(DHTPIN, HIGH);
+    delay(10);
+    digitalWrite(DHTPIN, LOW);
+    delay(18);
+    // then pull it up for 40 microseconds
+    digitalWrite(DHTPIN, HIGH);
+    delayMicroseconds(40); 
+    // prepare to read the pin
+    pinMode(DHTPIN, INPUT);
+    
+    // detect change and read data
+    for ( i=0; i< MAXTIMINGS; i++) {
+        counter = 0;
+        while (sizecvt(digitalRead(DHTPIN)) == laststate) {
+            counter++;
+            delayMicroseconds(1);
+            if (counter == 255) {
+                break;
+            }
+        }
+        laststate = sizecvt(digitalRead(DHTPIN));
+        
+        if (counter == 255) break;
+        
+        // ignore first 3 transitions
+        if ((i >= 4) && (i%2 == 0)) {
+            // shove each bit into the storage bytes
+            dht22_dat[j/8] <<= 1;
+            if (counter > 16)
+                dht22_dat[j/8] |= 1;
+            j++;
+        }
+    }
+    
+    // check we read 40 bits (8bit x 5 ) + verify checksum in the last byte
+    // print it out if data is good
+    if ((j >= 40) && 
+        (dht22_dat[4] == ((dht22_dat[0] + dht22_dat[1] + dht22_dat[2] + dht22_dat[3]) & 0xFF)) ) {
+        float t, h;
+        h = (float)dht22_dat[0] * 256 + (float)dht22_dat[1];
+        h /= 10;
+        t = (float)(dht22_dat[2] & 0x7F)* 256 + (float)dht22_dat[3];
+        t /= 10.0;
+        if ((dht22_dat[2] & 0x80) != 0)  t *= -1;
+        
+            //printf("Humidity = %.2f %% Temperature = %.2f *C \n", h, t );
+            s->humidity = h;
+            s->temperature = t;
+            return 1;
+        } else {
+            //printf("Data not good, skip\n");
+            return 0;
+        }
+}
+
+void getData(sensor *s) {
+    int tries = 100;
+    while (read_dht22_dat(s) == 0 && tries--) {
+       delay(1000);
+    }
+}