RockBot System

Rock Band Guitar

Getting Started

This guide describes how to modify the rock band guitar for the bot. A nearly/completely solderless (depending on how you fit it), easy-to-fit 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 Rock Band Guitar works

The rock band guitar is fairly similar to the guitar hero ones. It has a strum bar with up and down sensors, back start, D pad, etc.

The colour buttons, however are beautifully simple compared with the guitar hero ones. Instead of using eight wires for five buttons it has one common wire then ten more wires, five for the normal buttons and five for the solo buttons. The strum bar is slightly different, it has two reed switches instead of two press switches, probably to reduce mechanical wear.

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

The colour buttons have a negative common, it is the 6th wire from the right in the picture below, the other 5 right-most wires are the button control wires. The wires on the left are the solo button wires.

The board there connects the on-board plug to the socket that is on the neck wires, it is very simple to make and fit using 2.54mm pitch Pin plugs and sockets.

Fortunately the common wire (6th from the right, the pink one) is negative so we can control all those buttons with opto isolators, drawing the negative source from that common wire, below is a section of the schematic:

The connector SV5 is what goes to the usb board, 1-8 are control outputs 9 is common Gnd.

Neck 6 is the common negative, the others are switched for the buttons.

For strumming, back and whammy there are pairs of wires to be activated (for whammy its usually the middle and the 'inner' one but its best to check by 'shorting' them.

When connecting these pairs using a low voltage measurement setting on the meter check which is negative and which is positive, it will probably only read about 2 volts. Once you know which is which you can connect them to the other opto isolators. Here is the full schematic:

Once this is done, connect the SV5 wires to the USB board and you're ready to go!

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