diff --git a/examples/04.Communication/MultiSerial/MultiSerial.ino b/examples/04.Communication/MultiSerial/MultiSerial.ino
index d356f51..20fc441 100644
--- a/examples/04.Communication/MultiSerial/MultiSerial.ino
+++ b/examples/04.Communication/MultiSerial/MultiSerial.ino
@@ -17,6 +17,8 @@
   by Arturo Guadalupi
 
   This example code is in the public domain.
+
+  https://www.arduino.cc/en/Tutorial/BuiltInExamples/MultiSerialMega
 */
 
 
diff --git a/examples/04.Communication/ReadASCIIString/ReadASCIIString.ino b/examples/04.Communication/ReadASCIIString/ReadASCIIString.ino
index e49a989..bbd395b 100644
--- a/examples/04.Communication/ReadASCIIString/ReadASCIIString.ino
+++ b/examples/04.Communication/ReadASCIIString/ReadASCIIString.ino
@@ -17,6 +17,8 @@
   by Arturo Guadalupi
 
   This example code is in the public domain.
+
+  https://www.arduino.cc/en/Tutorial/BuiltInExamples/ReadASCIIString
 */
 
 // pins for the LEDs:
diff --git a/examples/04.Communication/SerialPassthrough/SerialPassthrough.ino b/examples/04.Communication/SerialPassthrough/SerialPassthrough.ino
index 81037eb..84824cf 100644
--- a/examples/04.Communication/SerialPassthrough/SerialPassthrough.ino
+++ b/examples/04.Communication/SerialPassthrough/SerialPassthrough.ino
@@ -20,6 +20,8 @@
 
   created 23 May 2016
   by Erik Nyquist
+
+  https://www.arduino.cc/en/Tutorial/BuiltInExamples/SerialPassthrough
 */
 
 void setup() {