added prompt for I2C scan

cubesatsim/cubesatsim.ino

@@ -4149,11 +4149,15 @@ void serial_input() {
        break;	
 		   
      case 's':
-     case 'S':
        Serial.println("Change to SSTV mode");	     
        new_mode = SSTV;
        break;	
-		   
+
+     case 'S':
+       Serial.println("I2C scan");	     
+       prompt = PROMPT_I2CSCAN;		
+       break;	
+   
      case 'i':
      case 'I':
        Serial.println("Restart CubeSatsim software");	     
@@ -4244,6 +4248,7 @@ void prompt_for_input() {
        Serial.println("f  FSK/DUV mode");	     
        Serial.println("b  BPSK mode");	     
        Serial.println("s  SSTV mode");	     
+       Serial.println("S  I2C scan");	   
        Serial.println("i  Restart");	     
        Serial.println("c  CALLSIGN");	     
        Serial.println("t  Simulated Telemetry");	     
@@ -4411,6 +4416,85 @@ void prompt_for_input() {
       else  
         Serial.println("off");
       break;	
+
+    case PROMPT_I2CSCAN:
+      Serial.print("I2C scan");
+
+/ --------------------------------------
+// i2c_scanner
+//
+// Version 1
+//    This program (or code that looks like it)
+//    can be found in many places.
+//    For example on the Arduino.cc forum.
+//    The original author is not know.
+// Version 2, Juni 2012, Using Arduino 1.0.1
+//     Adapted to be as simple as possible by Arduino.cc user Krodal
+// Version 3, Feb 26  2013
+//    V3 by louarnold
+// Version 4, March 3, 2013, Using Arduino 1.0.3
+//    by Arduino.cc user Krodal.
+//    Changes by louarnold removed.
+//    Scanning addresses changed from 0...127 to 1...119,
+//    according to the i2c scanner by Nick Gammon
+//    https://www.gammon.com.au/forum/?id=10896
+// Version 5, March 28, 2013
+//    As version 4, but address scans now to 127.
+//    A sensor seems to use address 120.
+// Version 6, November 27, 2015.
+//    Added waiting for the Leonardo serial communication.
+// 
+//
+// This sketch tests the standard 7-bit addresses
+// Devices with higher bit address might not be seen properly.
+//
+
+
+{
+  byte error, address;
+  int nDevices;
+
+  Serial.println("Scanning...");
+
+  nDevices = 0;
+  for(address = 1; address < 127; address++ ) 
+  {
+    // The i2c_scanner uses the return value of
+    // the Write.endTransmisstion to see if
+    // a device did acknowledge to the address.
+    Wire.beginTransmission(address);
+    error = Wire.endTransmission();
+
+    if (error == 0)
+    {
+      Serial.print("I2C device found at address 0x");
+      if (address<16) 
+        Serial.print("0");
+      Serial.print(address,HEX);
+      Serial.println("  !");
+
+      nDevices++;
+    }
+    else if (error==4) 
+    {
+      Serial.print("Unknown error at address 0x");
+      if (address<16) 
+        Serial.print("0");
+      Serial.println(address,HEX);
+    }    
+  }
+  if (nDevices == 0)
+    Serial.println("No I2C devices found\n");
+  else
+    Serial.println("done\n");
+
+  delay(5000);           // wait 5 seconds for next scan
+}		  
+		  
+		  
+        Serial.println("complete");
+      break;	
+		  
   }
   prompt = false;	
 }