The AGH1000 is connected between the Wii's video output and the TV or monitor's video input. The Wii's video output format is NTSC Composite Video. This means that all the information to properly drive a video monitor is present on a single wire - typically the yellow RCA connector. We used this composite video signal to generate signals that electrically press the correct notes and strum button at the correct time.

The system consists of four sections - the Analog Processing Board, the Digital Processing Board, the Driver Board, and the Opto-Isolator Board.

The Analog Processing Board is responsible for three basic functions:

1. Separate the composite video signal into signals for the Digital Processing Board. This section generates the digital signals ODD/EVEN, VSYNC, and BURST.

2. Generate a digital signal if the analog voltage of the video signal is above a certain level, called SLICE.

3. Under processor control, add a small voltage offset to the composite video signal that drives the video monitor to highlight a section of the screen. This signal is called HIGHLIGHT and is an input to this board.

The signals are connected to the Digital Processing Board through a 10 pin ribbon cable.

Read more about the Analog Processing Board HERE.

The Digital Processing Board is responsible for doing all the processing necessary to convert the digital signals from the Analog Processing Board to the Driver Board. It's an off the shelf development board called a Spartan-3 and is sold by Xilinx and others and contains a Xilinx FPGA. Instead of a microprocessor or microcontroller that sequentially steps through a program, the FPGA is a collection of gates that can be programmatically connected together to form concurrent processes that runs much faster than the video information it's trying to process. The program is written in VHDL, inside Xilinx's programming environment called ISE, compiled, downloaded into the board via the Digilent USB2 interface board, and runs on the FPGA. Read more about the Digital Processing Board HERE.

The Driver Board is simply a 74LS244 used to buffer the signals for their trip down the cable to the Opto-Isolator Board. Each output drives a corresponding Opto-Isolator on the Opto-Isolator Board. It's connected to the Digital Processing board via a 10 pin ribbon cable.

The Opto-Isolator Board is mounted inside the Guitar Hero's guitar. It's responsible for electronically pressing the buttons. There are 6 opto-isolators on this board. One for each of the 5 colors (Green, Red, Yellow, Blue, and Orange), and one for activating the strum bar. We mounted a male RS232 connector on the side of the guitar to facilitate the connection between this and the Driver Board so we could use any standard DB9 serial cable to connect the system to the guitar.

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