Diff: Dht11.cpp

Revision:

0:c1da310d3e8a

Child:

1:5da6f6de3e42

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Dht11.cpp	Sun Feb 15 02:09:00 2015 +0000
@@ -0,0 +1,86 @@
+#include "Dht11.h"
+
+Dht11::Dht11(PinName p) : _pin(p) {
+    // Set creation time so we can make 
+    // sure we pause at least 1 second for 
+    // startup.
+    _timer.start();
+}
+
+// Return values:
+// DHTLIB_OK
+// DHTLIB_ERROR_CHECKSUM
+// DHTLIB_ERROR_TIMEOUT
+int Dht11::read()
+{
+    // BUFFER TO RECEIVE
+    uint8_t bits[5];
+    uint8_t cnt = 7;
+    uint8_t idx = 0;
+
+    // EMPTY BUFFER
+    for (int i=0; i< 5; i++) bits[i] = 0;
+    
+    // Verify sensor settled after boot
+    while(_timer.read_ms() < 1500) {}
+    _timer.stop();
+
+    // Notify it we are ready to read
+    _pin.output();
+    _pin = 0;
+    wait_ms(18);
+    _pin = 1;
+    wait_us(40);
+    _pin.input();
+
+    // ACKNOWLEDGE or TIMEOUT
+    unsigned int loopCnt = 10000;
+    while(_pin == 0)
+        if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
+
+    loopCnt = 10000;
+    while(_pin == 1)
+        if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
+
+    // READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT
+    for (int i=0; i<40; i++)
+    {
+        loopCnt = 10000;
+        while(_pin == 0)
+            if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
+
+        //unsigned long t = micros();
+        Timer t;
+        t. start();
+
+        loopCnt = 10000;
+        while(_pin == 1)
+            if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
+
+        if (t.read_us() > 40) bits[idx] |= (1 << cnt);
+        if (cnt == 0)   // next byte?
+        {
+            cnt = 7;    // restart at MSB
+            idx++;      // next byte!
+        }
+        else cnt--;
+    }
+
+    // WRITE TO RIGHT VARS
+    // as bits[1] and bits[3] are allways zero they are omitted in formulas.
+    _humidity    = bits[0]; 
+    _temperature = bits[2]; 
+
+    uint8_t sum = bits[0] + bits[2];  
+
+    if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;
+    return DHTLIB_OK;
+}
+
+int Dht11::temperature() {
+    return(_temperature);
+}
+
+int Dht11::humidity() {
+    return(_humidity);
+}