DIY Stompboxes => Digital & DSP => Topic started by: Sonic Wizard on November 04, 2009, 03:51:19 PM

Title: Help: CMOS, PICs and Matrix Switching
Post by: Sonic Wizard on November 04, 2009, 03:51:19 PM
I need help developing a design for an effects switching system. The design has two main requirements:

1) Preset effect and amp channel combinations
2) Small size and weight

1) Preset effect and amp channel combinations
To accomplish this goal, I've been working on an effects switcher for a while, based on R.G. Keen's articles on CMOS logic. The one that interested me most was the Programmable FX Switcher with Amp Controls: (
I like the functionality: metal on metal relay signal switching, flexible routing, preset combinations including amp channels. I don't need to switch effects in any order. It's also too big for my needs when you add all the other boxes (effects, patch switcher) that are needed for it to work.

2) Small size and weight
To reduce the footprint and number of boxes on the floor, I want to integrate the effects themselves into the same enclosure. This is the arrangement I've come up with:

A) Effects Hub. Contains three analog effects circuits, built in modular format with 4 connections on each module for input, output, ground, and 9V DC. (Pots are included in the modules.) Also contains manual switches for each effect and the circuitry to put it in one of two modes. Manual Mode means that the manual switches are independent and work like regular stomp switches. One per effect, bypassed or engaged. Patch Mode means that the effect switching is controlled by the other box, the Patch Bank, which is connected with a multi-conductor control cable.

B) Patch Bank. Contains seven patch switches. Each patch gets a DIP for programming which effects are included. Jacks are included for two separate amp controls, also programmable on the DIP switches. Contains relays for the amp control switching. Contains an eighth switch to set it to Manual Mode.

When the Hub is not attached to the Patch Bank, it always runs in Manual Mode, i.e. like three stompboxes in one enclosure. When the Hub and Patch Bank are connected, stepping on a patch switch puts it in Patch Mode. Stepping on the eighth manual switch puts it back in Manual Mode. To switch from one patch to another only takes one step - step on the new patch and the previous one will switch off.

The idea behind the whole thing is to build something that a gigging guitar player will be able to use. It should offer a reasonable variety of standard boutique-quality analog effects, which the player can put in a chosen order. They can bring just the Effects Hub to have a three-in-one box if they're traveling light to a jam. For bigger shows, they can add the Patch Bank for preset combos of effects and amp channels. Ideally, the whole thing would be expandable, at least to the size of six effects and two amp controls. It should run on a single power supply. I want to build this and sell it.

My problem is that I'm more of an entrepreneur and designer than a logic/programming person. I've been building analog effects for a while, but CMOS is daunting. It seems like PICs might be the better way to go for lower parts counts and smaller PCBs with program-based switching.

I've read through the posts on Peter Snowberg's Crossbar ( ( and other PIC-based projects. I need someone who is a logic and programming ninja, in the tradition of Peter Snowber and R.G. Keen (you guys want to chime in  :)?), and can help me flesh out the schematic for my project. I'm open to setting up a licensing agreement for design work. I can do the building; what I need is help designing a solid schematic and any needed code to make the machine work.