main.cpp

00001 #include "mbed.h"
00002 
00003 DigitalOut myled(LED1); // Activate LED
00004 DigitalIn mybutton(USER_BUTTON); // Activate button
00005 DigitalInOut data_pin(A0); // Activate digital in
00006 Serial pc(SERIAL_TX, SERIAL_RX); // Initialize UART connection
00007 // Use a terminal program (eg. TeraTerm).
00008 Timer tmr; //initialize timer
00009 uint64_t adat; // 64 bit variable for temporary data
00010 int i;
00011 
00012 // Function to initialize DHT11
00013 void dht_read(void) {
00014     data_pin.output(); // Set A0 as output
00015     // Initialize measurement > 18 ms low
00016     data_pin = 0;
00017     wait_ms(20);
00018     // After high and release the pin switch input mode
00019     data_pin = 1;
00020     data_pin.input();
00021     // Wait until the end of 80 us low
00022     while(!data_pin.read()) {}
00023     // Wait until end of 80 us high
00024     while(data_pin.read()) {}
00025     // 40 bit, 40 read out cycle
00026     for(i=0; i<40; i++) {
00027         adat = adat << 1; // Shift for new number
00028         tmr.stop(); // Stop timer if runs
00029         tmr.reset();  // Reset timer
00030         // Wait until pin
00031         while(!data_pin.read()) {}          
00032         tmr.start();            
00033         while(data_pin.read()) {}
00034         // If DHT11 HIGH longer than 40 micro seconds (hopefully 70 us)
00035         if(tmr.read_us() > 40) {
00036             // bit is 1
00037             adat++;
00038         }
00039     }
00040 }
00041 
00042 int main() {
00043     pc.printf("Read the DHT11 temperature and humidity sensor!\n"); //Welcome message
00044     while(1) {
00045         if (mybutton == 0) { // Button is pressed
00046             // Reset adat variable
00047             adat = 0;
00048             myled = 1; // LED is ON
00049             dht_read(); // Call the function
00050             // Send result through UART result
00051             pc.printf("Humidity: "); // Humidity
00052             pc.printf("%d", (adat  & 0x000000ff00000000) >> 32); // Humidity
00053             pc.printf("\n\r"); // Send a new line and carriage return.
00054             pc.printf("%d", (adat & 0x0000000000ff0000) >> 16 ); // Temperature
00055             pc.printf("\n\r");
00056             pc.printf("%d", adat & 0x00000000000000ff); // Checksum.
00057             pc.printf("\n\r");
00058             wait_ms(200); // Wait 0.2 sec till continue.
00059         } else {
00060             myled = 0; // LED is OFF
00061         }
00062     }
00063 }