Advice on Simple Switch

Hi all!

I've recently become interested in creating a custom MIDI footswitch controller with a couple added features to control my guitar effects processor. I think I have most everything worked out thanks to the excellent examples from the community, however there is one thing that I'm not certain about just yet.

One of the features I'm interested in adding is the ability to switch channels on my guitar amp. This is done using a 1/4" TRS phone plug where you connect tip to sleeve, ring to sleeve, etc. The amp supports the following combinations:

  • Tip open, ring open
  • Tip open, ring closed
  • Tip closed, ring open
  • Tip closed, ring closed

When closed, I've observed 14.76VDC and 12.39mA across each connection.

A pair of SPST relays seem pretty straightforward, but I was exploring other potential options like optocouplers or transistors and I'm curious on your thoughts as to the pros/cons for each.

I kind of like the idea of using something other than a relay. What component(s) would you recommend and why?

Thanks!

Is this switching part of the MIDI specification (or any other spec)? I don't think anyone will provide you with details of a solid state alternative to relays without knowing the details of what's being switched.

johndg:
Is this switching part of the MIDI specification (or any other spec)? I don't think anyone will provide you with details of a solid state alternative to relays without knowing the details of what's being switched.

Yes, my multi-effects unit will send a MIDI CC message that the Arduino will receive. Depending on the message, the Arduino will set the two switches appropriately (either opened or closed) as described in my first post.

My guitar amplifier has a 1/4" TRS phone jack that accepts a 2 button footswitch. Each button toggles a different setting on the amp. This is very common. What's a little unique about my amp is that it provides an alternative mode designed to allow external devices to switch the amp channels and voices. Rather than the default toggle mode, it accepts explicit instructions via the four open/closed combinations of tip-to-sleeve and ring-to-sleeve.

I want the Arduino to open and/or close two switches so the amp knows what channel and voice to switch to. I know I can do this with two SPST relay modules, but was curious whether other options may be viable, or perhaps even preferred.

Thanks!

pgfitzgerald:
. I know I can do this with two SPST relay modules, but was curious whether other options may be viable, or perhaps even preferred.

I understood the two SPST relays bit, what we don't have is the spec. of what the relays are switching.

pgfitzgerald:
When closed, I've observed 14.76VDC and 12.39mA across each connection.

Do we take this to mean that the contacts switch 15VDC at 12.5mA? If so, is it ground-referenced, or floating?

Great questions. I don't have schematics for the amp, so I don't know for sure. Edited to correct: I observe 100ohm resistance when I test between the TRS jack's shield and any other place on the chassis. Sounds like ground-referenced to me.

I was under the impression I just needed a switch of some sort that is capable of being triggered via the 5VDC signal from a digital pin on the Arduino and passing the ~15VDC/~12.5mA without burning up. After all, the included footswitch is just two latching SPST switches wired tip-to-sleeve and ring-to-sleeve respectively. It's quite possible my ignorance has led me to assume this was simpler than it truly is. :slight_smile:

Thanks!

For posterity...

I decided on a dual SPST NO solid state relay, LAA108:

LAA108 Datasheet by IXYS Integrated Circuits Division | Digi-Key Electronics

It's working perfectly for me. Here's a snippet of the circuit:

Yep, good shout. Relays (solid state or mechanical) are definitely the best solution, unless you know exactly what you're switching (ie you have the full circuit diagram of the device, or at least a completely-defined specification for what's being switched).

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.