Second is the character brick circuit. I chose PIC16F628A for each character brick, since it is cheap (around HKD$10 each if I buy at China). It has 4 analogs in so that I can use a piezo buzzer as a knocking switch, and internal 4MHz oscillator. It also provides enough pins for me to drive a custom made 7 x 5 LED matrix. And I still got 6 pins left for communication and other purpose. 
Testing board for the character bricks, knocking mechanism not yet implemented.
Third is the receiver, I chose PIC18F452 in the prototype stage, since I need to have enough space to store the data coming from the character bricks. In the testing stage, I need to connect the 7×5 LED matrix to check is it get the right data from the character bricks. So in the final product, I will use PIC18F252 to make the receiver smaller. Also, I want to test the serial communication between character brick and receiver work properly, I used an 8MHz Crystal to drive the PIC18F452 to make sure different speed microcontroller can communicate properly. Later I will change the Crystal to 20MHz powered oscillator to make sure it has stable MIDI output.
Testing board for the character bricks, MIDI not yet implemented.
