Diff: main.cpp

Revision:

0:2b4e5d360246

Child:

1:221a6fd3d62f

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Mon Oct 17 10:15:28 2016 +0000
@@ -0,0 +1,43 @@
+/*
+    Simple Program to use SFR05 or SFR04 in Single Pin Mode
+    Divide by 5.8 to give mm resolution from microseconds read of Echo pulse
+    Version 1.0a
+    M.Simpson 17/10/2016
+*/
+#include "mbed.h"
+
+DigitalInOut TriggerEcho(D8);                                   //Instance of the DigitalInOut class called 'TriggerEcho'
+
+Timer pulse;                                                    //Instance of the Timer class called 'pulse'
+
+float GetDistance();                                            //Function Prototype
+
+int main() {
+     float Distance;                                            //Assign a local variable for the main function
+     pulse.start();                                             //Start the instance of the class timer        
+     
+     while(true)                                                //Continuous loop always true
+     {
+        Distance=GetDistance();                                 //Get the value returned from the function GetDistance()
+        printf("Distance %.0fmm\n\r",Distance);                 //Send the value to the serial port for monitoring purposes
+        wait_ms(250);                                           //Wait for 250ms
+     }    
+}
+ 
+float GetDistance(){                                            //Function Name to be called
+     int EchoPulseWidth=0,EchoStart=0,EchoEnd=0;                //Assign and set to zero the local variables for this function
+     TriggerEcho.output();                                      //Make the DigitalInOut an Output to drive a signal
+     TriggerEcho.write(1);                                      //Signal goes High i.e. 3V3
+     wait_us(100);                                              //Wait 100us to give a pulse width
+     TriggerEcho.write(0);                                      //Signal goes Low i.e. 0V
+     TriggerEcho.input();                                       //Make the DigitalInOut an INPUT to accept a signal
+     pulse.reset();                                             //Rest the instance of the Timer Class
+     while(TriggerEcho.read()==0&&EchoStart<25000){             //wait for Echo to go high
+            EchoStart=pulse.read_us();                          //AND with timeout to prevent blocking!      
+     }
+     while(TriggerEcho.read()==1&&(EchoEnd-EchoStart<25000)){   //wait for echo to return low
+        EchoEnd=pulse.read_us();                                //or'd with timeout to prevent blocking!   
+     }
+     EchoPulseWidth=EchoEnd-EchoStart;                          //time period in us
+     return (float)EchoPulseWidth/5.8f;                         //calculate distance in mm and reurn the value as a float
+}
\ No newline at end of file