I am working on a project which uses a set of sensors (HC-SR04). These sensors use pins 2 to 13 of the Arduino Uno. Here you can find the board:
I also want to add an MP3 shield (VS1053B) to it and it fills all the pins on Arduino. So I decided to add an Arduino Mega and add the sensors to it and use the Arduino Uno and MP3 shield. The problem is with connecting these two Arduinos. As I said the MP3 shield fills A4 and A5 pins too, so I can not use them to communicate with the Mega. What other options do I have?