relay board for pedal switching

[amonras]

Hi people,

This is my first post, so please forgive me if I do not explain properly

After having built a few analog pedals, I am now thinking of an Arduino-based signal router. I want to fit all my gear inside a badass pedalboard. As I am still learning, I want to focus on scalability, as my initial project will probably be much smaller than the final result, so I'd like to start with something which is already easily scalable.

After looking at various posts about relay switching, I am overwhelmed with the variety of options. NO/NC/latching? opto/mechanical? 2pdp/3pdt?

I have thought of using a board of 3pdt relays, in order to have true-bypass and a led signal for each effect that is active, but I could also operate the leds by software. My concerns are:

- audio signal quality (I don't want the control current to mess with my signal)
- Latency (I guess anything within 10-20ms should be enough)
- Clipping (I'd like to keep this at a minimum)
- Power consumption? One idea is to fit the pedal board with a battery, so keeping the power consumption at a minimum might also be also an issue. For this reason maybe the best is a latching relay, but these seem more expensive, and have other drawbacks... I am open to trading this for convenience...

* There are probably many other things that I haven't considered, so I'm open to suggestions.

What do you think is the best fit for me?

[amz-fx]

An Arduino should be able to control enough relays for your pedals switching, and manage the LEDs on another port.

Non-latching mechanical DPDT relays are the easiest for this type of project. Panasonic, Omron, Axicom and many others make devices that are suitable.

Audio signal should be excellent and the control feedthrough will be minimal if you route your control wires away from the audio wires.
Latency is not an issue with non-latching relays. They switch fast enough that you won't notice.
Clipping? No problem.
Power? An Arduino, the LEDs and the relays will draw as much current as the pedals so it would be best to give them a separate power supply or battery.

A problem that you might encounter is that there may be a pop as the audio is switched if all of the pedals are not designed properly. The relays should be as quiet (or more quiet) than a mechanical footswitch, but true bypass pedals without pulldown resistors may pop, and some pedals with electronic switching (like Boss) will pop when put in a bypass loop.

regards, Jack

[R.G.]

After having built a few analog pedals, I am now thinking of an Arduino-based signal router. I want to fit all my gear inside a badass pedalboard. As I am still learning, I want to focus on scalability, as my initial project will probably be much smaller than the final result, so I'd like to start with something which is already easily scalable.

There is a wealth of information on signal routing options on geofex.com. See:
http://www.geofex.com/article_folders/rmtswtch/rmtsw.htm
http://www.geofex.com/Article_Folders/pffootsw.pdf
http://www.geofex.com/article_folders/fxswitchr/fxswitchr.htm
http://www.geofex.com/article_folders/cd4053/cd4053.htm
http://www.geofex.com/Article_Folders/bosstech.pdf
http://www.geofex.com/article_folders/bypass/bypass.htm

After looking at various posts about relay switching, I am overwhelmed with the variety of options. NO/NC/latching? opto/mechanical? 2pdp/3pdt?

In general, you want miniature DPDT relays for pedalboard switching unless there is some other explicit need. See:
http://www.geofex.com/article_folders/relays/relays_for_switching_audio_signa.htm
See the relay article below on the NO/NC/latching issue. A DPDT relay has two NO and two NC throws. Latching is unrelated to the poles/throws.

I have thought of using a board of 3pdt relays, in order to have true-bypass and a led signal for each effect that is active, but I could also operate the leds by software. My concerns are:

That's one way to do it, but in general if you have a logic system that remembers which relays should be on, just have that power the LED. 3PDT miniature relays don't really exist (never found one) and aren't needed. 3PDT non-miniature relays are quite expensive and much larger, noisier, etc. than miniature PCB mount relays.

- audio signal quality (I don't want the control current to mess with my signal)

This is controlled by how well you wire the power to/from the relays and are careful about grounding much more than the relays or control signal.

- Latency (I guess anything within 10-20ms should be enough)

Anything under 50mS is generally OK. Well done software should be much, much under this, and the thing that drives latency will probably be debouncing the switch in software before driving the relays. Some mechanical footswitches may bounce for 20-50mS on their own. You can't do a good job of switching before the switch quits bouncing.

- Clipping (I'd like to keep this at a minimum)

Not an issue with relays. Might be an issue with JFET switching.

- Power consumption? One idea is to fit the pedal board with a battery, so keeping the power consumption at a minimum might also be also an issue. For this reason maybe the best is a latching relay, but these seem more expensive, and have other drawbacks... I am open to trading this for convenience...

A non-latching relay needs power to the relay coil continuously to hold it in its energized position. This is different for each relay, but for miniature pcb relays, it's about 5-50ma. An LED needs 2-20ma continuously. If you have many loops, you find the relay current and LED current, then multiply by the number of loops (they can all be on at once) and add the current used by your logic controller.

It's easy to use upwards of a quarter to half an amp in relay currents for large, complex pedalboards if you use non-latching relays. This is the big reason for spending the extra electronics parts to drive latching relays - it makes battery operation possible.

But it's only possible if you use a low-current logic controller. The Arduino is not necessarily a low-current device, although I could not find a clear statement of its power supply use independent of its I/O pins.

That's one reason for going with either CMOS hard-logic designs or bare microprocessor designs. Both of these use much less current than even one relay, so you can ignore their power use in the total. And once you have a very low power controller that you can program, you can use a latching relay to eliminate the idle current of the relays, leaving only the power to drive the LEDs.

* There are probably many other things that I haven't considered, so I'm open to suggestions.

The user interface is demanding. How will you tell the logic which combinations of loops to activate when you select a prearranged patch? There's another whole can of worms there.

What do you think is the best fit for me?

Reading. Lots of reading.

[amonras]

There is a wealth of information on signal routing options on geofex.com. See:
http://www.geofex.com/article_folders/rmtswtch/rmtsw.htm
http://www.geofex.com/Article_Folders/pffootsw.pdf
http://www.geofex.com/article_folders/fxswitchr/fxswitchr.htm
http://www.geofex.com/article_folders/cd4053/cd4053.htm
http://www.geofex.com/Article_Folders/bosstech.pdf
http://www.geofex.com/article_folders/bypass/bypass.htm

That's a gold mine right there! Thanks!

A non-latching relay needs power to the relay coil continuously to hold it in its energized position. This is different for each relay, but for miniature pcb relays, it's about 5-50ma. An LED needs 2-20ma continuously. If you have many loops, you find the relay current and LED current, then multiply by the number of loops (they can all be on at once) and add the current used by your logic controller.
It's easy to use upwards of a quarter to half an amp in relay currents for large, complex pedalboards if you use non-latching relays. This is the big reason for spending the extra electronics parts to drive latching relays - it makes battery operation possible.

But it's only possible if you use a low-current logic controller. The Arduino is not necessarily a low-current device, although I could not find a clear statement of its power supply use independent of its I/O pins.

That's one reason for going with either CMOS hard-logic designs or bare microprocessor designs. Both of these use much less current than even one relay, so you can ignore their power use in the total. And once you have a very low power controller that you can program, you can use a latching relay to eliminate the idle current of the relays, leaving only the power to drive the LEDs.

That's one good reason to begin with a less ambitious project and leave the battery aside for the moment.

The user interface is demanding. How will you tell the logic which combinations of loops to activate when you select a prearranged patch? There's another whole can of worms there.

That's true, but I'm much more experienced at programming than at fiddling with electronics. I'll take care of that... For the moment I'll just emulate standard individual footswitches, but eventually I'll be able to run in "basic" mode, or in "program" mode... The basic mode is quite straightforward to design... the "program" mode is much more vague at the moment... I guess I'll go to shops and try different pedalboards to see how they talk to the user...

Reading. Lots of reading.

Acknowledged! I do research for a living, so I know well what you mean! Thanks a ton to both replies!

[blackieNYC]

Also "Tone God Wicked switches" article. This and RG's 4053 circuits deserve a look when embarking on something like this.
And, Smallbear Electronics carries a "mono monster" DPDT relay pcb, with parts. AMZ also sells a similar product. Very easy to use with a programable controller or not
Then there is the "monoprice" programmable 8-looper for about a third of the price of all its competition. Haven't seen one up close.