Fixed bug in short-circuit detection for MEGA

The short-circuit code polled the track current every 10
“milliseconds.”  But Arduino millis() is based on TIMER-0 settings
which are changed in DCC++ Base Station.  The actual polling was closer
to every 1 millisecond.  When Base Station for the Mega for updated to
utilize TIMER-3 instead of TIMER-0, the millis() function now really
did count milliseconds, and 10 milliseconds between each track-current
sampling was too long.  Changed the code so that for the Mega, the
current sampling time is defined as 1 (instead of 10), representing an
actual 1 millisecond as desired.

DCCpp_Uno/CurrentMonitor.cpp

@@ -22,7 +22,7 @@ CurrentMonitor::CurrentMonitor(int pin, char *msg){
 boolean CurrentMonitor::checkTime(){
   if(millis()-sampleTime<CURRENT_SAMPLE_TIME)            // no need to check current yet
     return(false);
-  sampleTime=millis();
+  sampleTime=millis();                                   // note millis() uses TIMER-0.  For UNO, we change the scale on Timer-0.  For MEGA we do not.  This means CURENT_SAMPLE_TIME is different for UNO then MEGA
   return(true);  
 } // CurrentMonitor::checkTime
 

DCCpp_Uno/CurrentMonitor.h

@@ -13,9 +13,14 @@ Part of DCC++ BASE STATION for the Arduino
 #include "Arduino.h"
 
 #define  CURRENT_SAMPLE_SMOOTHING   0.01
-#define  CURRENT_SAMPLE_TIME        10
 #define  CURRENT_SAMPLE_MAX         300
 
+#ifdef ARDUINO_AVR_UNO                        // Configuration for UNO
+  #define  CURRENT_SAMPLE_TIME        10
+#else                                         // Configuration for MEGA    
+  #define  CURRENT_SAMPLE_TIME        1
+#endif
+
 struct CurrentMonitor{
   static long int sampleTime;
   int pin;