relay-bypass

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Soft touch relay bypass for DIY guitar pedals

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# Relay Bypass for DIY Guitar Pedals

Visit <https://mas-effects.com/relay-bypass> to purchase pre-made PCBs and pre-programmed AVR ICs.

Build documents here: <https://mas-effects.com/relay.pdf>

This repository contains all you need to build your own relay bypass PCB,
or hack at the one I provide.

This is a true-bypass module that provides:

* Soft touch, momentary switches can toggle your DIY guitar pedal, using a relay to provide true bypass.
* Quick tap to switch between engaged and bypass, or hold the footswitch down to temporarily toggle until you release it
* Fits easily in a 1590A
* Optional optocoupler muting can be enabled with a switch or jumper to mute any popping your circuit might exhibit while switching
* Hold when powering on to toggle between remembering bypass state (LED blinks 5 times), auto-on (3 blinks), or auto-off (4 blinks)
* VERY cost effective. [Shop now](https://shop.mas-effects.com/collections/diy/products/relay-bypass).
* Totally free and open source

## Build Instructions

This is a pretty quick and easy build. All of the surface mount (SMD) components come pre-soldered. You simply need to add the relay, optocoupler (optional), IC, voltage regulator, and capacitor.

Mount a normally-open, momentary SPST switch on the PCB next to the relay using double-sided foam tape.

## Optocoupler Muting

If you connect the 2 pads labeled J1 with a jumper or a switch, this will tell the IC to momentarily mute (35ms) the signal while switching. This can be useful if you have a circuit that pops when engaged.

This needs to be enabled in the firmware. If you buy from me the firmware may disable this if you didn't get an optocoupler, unless you ask specifically for the behavior to be enabled.

## Multiple LEDs

By default you can connect the LED pad to the anode of an LED (in series with a current-limiting resistor) to indicate status.

If you want to use multiple LEDs or need more current than the voltage regulator can provide, then simply use the 5V signal (with an appropriately sized resistor) to drive a transistor. The size of the resistor should limit the base current so the collector current is about 15x greater.

## AVR Microcontroller

An AVR microcontroller is used at the heart of this module.  You can use either an ATtiny13 or ATtiny85.  The code for this is in the [relay-bypass folder](./relay-bypass/relay-bypass.ino).  You'll find there are a handful of `#define` statements to allow you to easily change its behavior.

## Versions:

1.49 uses the 1.4 PCB and same hardware setup, but adds memory to the bypass state. By default it will remember whether the effect is engaged or bypassed (and uses wear leveling to store this). Holding the switch down at startup will toggle the behavior.

1.4 is the latest version in the root of this repository. It uses a latching relay for slightly reduced power consumption.

1.3 also uses a latching relay, but is not as DIY-friendly if you scratch-build (from a kit, however, it's exactly the same as V4). It requires you to write a fuse to disable the RESET pin and turn it into a GPIO pin. After doing this you can't re-program the ATtiny without special equipment. i.e. if you're not careful you may waste some microcontrollers.

1.2 has all the same features as later versions, but uses a non-latching relay instead.

## COPYRIGHT and LICENSE (MIT)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

relay-bypass

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