Noise Floor interface board collection

This is set of interface boards to speed effect pedal development, continuing my efforts to learn PCB design with KiCAD.

IO and Switch boards

The first board is an audio input and power board, featuring:

• Switched DC barrel jack supporting either a 9VDC center negative supply or 9V battery
• Mono audio jacks w/ switched input circuit (ring/ground shorted to sleeve on insertion)
• Basic power input protection

The IO PCB is designed to fit in a standard 125B enclosure.

The second board simplifies effect bypass via a 3PDT switch adapter with an LED indicator.

Connectivity (cabled)

IO, Effect, and Switch boards are connected using four-circuit Molex PicoBlade connectors.

Headers are labelled symmetrically from the perspective of the IO board:

• S1 on IO Board <-> S1 on Switch Board
• S2 on IO Board <-> S2 on Switch Board
• E1 on IO Board <-> E1 on Effect Board

UX PCB (experimental)

The third and newest (experimental) board is a UX board providing a standard superset of potentiometers and switches. It is intended to connect to an effects board using two 25-position Amphenol "Conan Lite" board-to-board connectors.

The current iteration of the UX board supports six potentiometers and three SPDT switches, but alternative control layouts are an obvious extension. Each potentiometer on the current prototype can be adjusted using optional parallel resistors (SMD 1206) to tweak the taper and total resistance.

Connectivity (board-to-board)

The effect and UX boards are connected using Amphenol "Conan Lite" board-to-board connectors. Only a single UX board variety currently exists, supporting a superset of six potentiometers and three SPDT switches. As the UX board is in the experimental/proof-of-concept phase, the pin assignment should be considered preliminary and subject to change.

Current connector allocation:

• 6x Potentiometers x 3 (CCW, Wiper, CW) = 18
• 3x SPDT switches x 3 (NO, COM, NC) = 9
• 4x Reserved for ground
• Total used: 31
• Remaining for expansion: 19

Ideas for future boards / changes:

• Allocate connector positions for a single DPDT switch (+3, reusing 3 from an existing SPDT)
• Incorporate linear potentiometers into an alternate IO board
• Allocate at least 12 positions for "flexible use" (enough to support a 4PDT switch)
• Allocate positions to drive (RGB?) LEDs with standardized current-limiting resistors

Schematic PDF

Credit

The original idea and specific bypass circuit is inspired by many manufacturers of utility PCBs and well-known circuits for 3PDT-based effect bypass, notably PedalPCB's 3PDT breakout, augmented to suit my needs.

Thanks as always to the folks on the freestompboxes.org forum for feedback and suggestions.

Potentiometer, 3PDT footswitch, and DC barrel jack 3D models courtesy Vasily Kashirin.

SPDT toggle switch 3D model courtesy Stephanie Schwecke.

Conan Lite footprints adapted from the 51-position footprints available from SnapEDA: Header, Receptacle.(Additional license details). 3D models courtesy Amphenol.

I am not affiliated with any of the brands, sites, or products named in this overview.

Future plans

• Build an IO board that includes a TRS expression pedal input (started this way, but found it hard to fit in a 125B enclosure)
• Support stereo operation via relays, optoisolators, or a "millenium" switch

Versioning

My pcb designs utilize the following versioning scheme (I'll add to this as I produce more revisions):

• v0.0XX: A candidate design that has not yet been produced and tested.
• v0.XX: A design that has been produced, tested, and any initial errors addressed.

Name

The name Noise Floor is a reflection of the function of the board (a substrate for pedals and bypass circuit) and security nerdery.