RockBot System

Guitar Hero Guitar

Getting Started

This guide describes how to modify the guitar hero guitar for the bot. A kit version is available in the Shop.

Tools you will need:
  • A Soldering Iron & Solder
  • A Multimeter
  • Wirecutters
  • Some tools for making a hole in the case for the connector

Components Used:

  • 2 x Quad ILQ74 or ISQ74 Opto Isolators
  • 1 x 100 Ohm Resistors

How the Guitar Hero Guitar works

The controller has a double switch strumming system which is easy to interface with along with the back button and whammy, however the coloured buttons were clearly concieved by a fool.

5 buttons use 8 wires and strange pair cominations to detect button presses, these are the pairs:

GH2 Controller:
Green:  1 and 8
Red: 2 and 7
Yellow: 2 and 5
Blue: 1 and 6
Orange: 3 and 4
GH3 Controller:
Green:  1 and 8
Red: 2 and 7
Yellow: 2 and 6
Blue: 2 and 3
Orange: 4 and 5

Beware: I have a friend in Canada who attempted this and found the wiring of his guitar to be different. The best way to be sure is take out the 'button board' and check it! See below:

Opto Isolators

I will explain (briefly) how opto isolators work as they are key to the drums and guitars.

The the GH3Bot I used relays for simplicity but they are slower to respond than opto isolators because of the mechanical delay.

From Wikipedia:

In electronics, an opto-isolator (or optical isolator, optocoupler, photocoupler, or photoMOS) is a device that uses a short optical transmission path to transfer a signal between elements of a circuit, typically a transmitter and a receiver, while keeping them electrically isolated — since the signal goes from an electrical signal to an optical signal back to an electrical signal, electrical contact along the path is broken.

The ILQ74 or ISQ74 is a quad optoisolator, four isolators in one housing with NPN phototransistors.

Each opto isolator has 4 pins, two for the light source (usually an infra-red LED) and two for the light sensor (usually a phototransistor).

An NPN phototransistor takes negative and switches it to the output (an PNP one would take positive and switch that). This means that polarity (the negative and positive) pins are crucial.

Be wary if using different opto isolators as they can have different pin configurations, for example a single opto isolator could be like:

Where pin 1 is + LED, 2 is -LED, 3 is the output and 4 is - In. (These are not the techical names).

However some double or quad ones alternate the pin pairs, imagine this is a chip:


2 & 3 would be - and 1 & 4 would be +, and 5-8 would also be similar.


How control the Guitar

There are 8 wires that run up the neck (gh2) or to the neck (gh3) you must tap into each one, and know the number of each (1 to 8), the numbers are marked on the PCB boards in the guitar.

Each pair has to be switched for the buttons using an opto isolator. Usually the lower value numbers are negative, but its best to check with a multimeter. There are common wires, which in my experience are the negative ones, this is not a problem just wire it up as it should be.

The schematic below is to show how a GH2 guitar should be wired (bare in mind my previous comment that some are differnet, check first!):

Once you have the colours button pairs sorted the rest is relatively easy. There is a 100 Ohm resistor beween the common of the optoisolator LEDs and ground.

Copyright © Paul Ridgway 2009 | Pictures by Amanda Taylor | HTML Layout & Base code by James Ridgway