ABCD Pedal Switcher

[jonathansuhr]

I like building pedalboard utility stuff in my free time and was wondering if there was something like this out there already.

Wanted to figure out some way to make a four pedal switcher that basically doesn't allow you to have more than one pedal on at once, but can be bypassed if I press the switch of the engaged loop. My assumption is that MIDI would be the only way to do this. Anyone have any ideas to make this work?

[Seljer]

Though you might be able to pull it off with standard logic ICs or latching relays, these days the easiest way is accomplish what you want is with a microcontroller, wire four switches to the digital inputs, wire four transistors to drive four relays (to do the actual audio switching) to the digital outputs, program it and you're done.

If you're new to microcontrollers and/or programming get an Arduino board. You can get it for under $20 and you don't need any fancy external programmer, just a regular USB cable. There's plenty of example code out there as the platform is basically aimed at beginners (but still capable of quite a lot)

[R.G.]

If you're willing to use a separate fifth footswitch for "bypass all", it gets easy.

The one-of-N switcher at geofex will do that. It's a single CMOS chip that has eight clocked data latches. Diodes and timing resistor-capacitor pairs let any one input work the clock, but only let data into one of the latches. So pressing any footswitch clocks "active" into its latch, but the other, inactive inputs are all clocked to "inactive". This works for up to eight footswitches with one chip.

So you have the output from each latch work a relay or JFET switch or CMOS switch to make the signal do what you want. One of four pedals or a bypass is easy enough.

[Processaurus]

The circuit at Geo is a very  handy one, for doing radio pushbutton type logic, where you push one button and it resets the others.  It could take a fifth stompswitch and make that the bypass switch.

The original poster is asking for something unfortunately more complicated, by wanting to have a second tap on the switch of the selected channel to put it into bypass.  Here is a CMOS version of that circuit designed before I learned basic programming.  It takes quite a few discreet logic chips (6).  If I were doing it over I would use a PIC, it would be a good beginner's programming project, being a simple state machine (a logic machine that looks at a number of inputs and generates a state for the outputs based on the inputs) type design.

It uses a cap that takes a moment to charge up in power on to start it up in a bypassed state, rather than something random, or illegal.

Note the bypass logic is inverted, being off when bypassed, and on when a channel is on.  This could be made to be a hi signal when bypassed by tacking on one of the unused inverters.

For reading the schematic, the labels in red ("Ch A Sw", "PWR RST", etc.) are net identifiers, all of the wires with the same label are connected together.  The chips have unnecessarily complicated names from my parts library, but are regular 40xx series logic.  For example an HCF4072BMI is a CD4072.

[vigilante397]

It sounds like a programmable looper might be a convenient fix for you. I just built this one from a board and chip a forum member designed and sold me pretty cheap.



You can program "patches" of any combination of the pedals plugged in, or in Bypass mode it functions like a true bypass looper. It's super cool.