optocoupling bypass anyone?

[pinkjimiphoton]

was just enjoying my version of st paddy's day libation cof cof 
while watching this video on tube'o you:

and i got to thinkin' to myself, hey self, what if ya was to use this in a guitar bypass kinda circuit dealio
where high gain makes switches clicky or problematic <or really, just cuz maybe it would work, and i'm nuts enough to ponder
such implausibles>....

i mean, basically, it could be used as a relay, right? and with the cheapest possible freekin stompswitch... this opens up some interesting possibilities to me... like having a box on a stand where i could reach knobs, and the footswitch(es) on the floor somewhere else, or whatever...

sorry. dachshund puppy just learned to bark and is trying to destroy my hearing, brains (?) and patience... so hard to think with the godawful racket, i guess a bee farted in china or something... anyways..

so was thinking, if using an opto coupler or even rolling your own, you can turn stuff off and on silently and electronically and remotely, without having to have the audio in the run at all, right?

so say, have it set up to flip flop alternately between one opto coupling circuit where the phototransistor turns on and lets the guitar signal straight thru as an electronic version of a true bypass, or routes it thru the circuit board in the other orientation. seems to me should be able to, with one pushbutton, to literally remotely true bypass the whole mess, but use light instead of mechanical switching.

or did i drink wayyyyyyyy too much tekeelye last nite?

just seemed like in addition to being the bane of clicking stomps echoing thru time, the possibility of just having simple controls remotely, like a relay switching in a guitar amp could be really useful in some circumstances.

i did a quick search, and found all kinds of info, but nothing regarding this kind of use.

do ya think it's possible?

should i waste the time and money and fall down a rabbit hole for shits n giggles?

ideas?

pink, you insane, or pink, it's cool....
remember
him the pink one be just an egg
a 10-toed freak
of
a monkey
with a broken breadboard.....

curious to hear folk's thoughts. pretty sure it may be cheaper or compatible price wise with mechanical switching.
a quick g-g-g-google shows the chips seem to be between 50 cents and a buck or so.

besides, if for no other reason, we need to see if the idea may have merit, just because it's there,
like a silicon mountain in the himilayahs or something...

[digi2t]

Bro, didn't you already go down this rabbit hole?
https://www.diystompboxes.com/smfforum/index.php?topic=117272.0

Anyway, here's what I found...

https://shop.pedalparts.co.uk/product/optopuss

https://1776effects.com/products/opto-tron-optical-bypass

https://www.musikding.de/Optotronic-Switch-Bypass-kit

https://rullywow.com/product/detour-optical-bypass-pcb/?doing_wp_cron=1647564808.0758810043334960937500

Phil and I have used the opto/relay angle for a few projects. In this case the opto only does the muting work while the signal gets switched by the relay. More parts? Yup. More expensive? Sure. Complex? Absolutely. But I think I prefer having the signal go through a relay than a MOSFET at any moment. It's as close to a mechanical 3PDT you'll get, without the ker-chunkiness (stole that one from Gov_Lacky. Thanks Greg!).

[Mark Hammer]

With any sort of bypass system/family, one has to make a distinction between bypass preventing something from "working", and permitting ANY amount of audio signal, no matter how small, getting through.  So, an optocoupler may cause enough of a change that the thing one is hoping to switch *from* no longer works.  This is essentially what Dino described.  That is, the relay is the thing that does the actual switching and completely changes what signal is leaving the pedal, and the optocoupler is causing enough of a change to make the relay go this way or that.

Over the decades here, you'll recall many have posted that their FET-switched pedal was still "leaking" effect signal, even in bypass.  FETs, and probably any bipolar transistor as well (as used in optocouplers), can still provide more than zero ohms resistance in one state, and less than infinite resistance in the other.  Not ALWAYS, of course, or else no one would use them for switching purposes, but sometimes.

The advantage of optocouplers is that they can make remote actuation of the "real" switch possible, conceivably by things like momentary SPST soft-touch switches.

[amptramp]

I always liked the idea of optoelectronic connections between stompboxes and the amplifier because you get ground isolation for safety and noise elimination.  A linear coupler such as this one:



could be redesigned to use a flip-flop of the kind used in Boss pedals to drive a transistor that is grounded and is connected to the bottom of R3.  The flip-flop controls drive transistors through an R-C time constant that avoids sudden switching that would cause switch pops and two of these optolinear stages would be used, one for the effect input and one for the effect output.  You switch between them to select effect of bypass.

The receive side would have parallel phototransistors, one from the bypass and one from the effect side.  The one that was deselected would go dark and pass no current because its associated LED would be off and the only one in control would be the selected one.  So imagine two of the circuit blocks in the diagram above with transistors at the bottom of R3.  the transistors would be driven from opposite sides of a Boss-type flip flop with a time constant to the transistors to avoid switch popping.

This would require a separate opto cable for bypass and effect if it was done with opto cables but if you could take an isolated power supply between each pedal, you could do it on one board with no opto cables - just ordinary jacks and cables.

A refinement would be to reverse the position of the driver and feedback LED's in the circuit and use the transistors to short out the LED's that couple to the receive side.  That would eliminate any disturbance to the current drain on the input side and would allow R3 to be independent of transistor saturation voltages.

This is a better rabbit hole to fall down.  Say hello to Alice when you get there.

[pinkjimiphoton]

thanks brothers, i guess what i was really thinking was it seemed like this could be used to do exactly what you suggest... remote trigger an onboard relay in an amp or a rack or something.

as usual, i don't really know enough to really describe what i was talking about...

but i was thinking a simple spdt switch controls say two optocouplers... set so one lights up an led, and the other extinguishes it each time you flop the switch... off/on, right? but use the led's that get illuminated to open or close the audio circuit, if that makes any kind of sense... even an led/ldr, right? i'd assume that dark, with an ldr inline, 60 ohms or so wouldn't matter much to the signal, and that lit, at 10megs or so it would effectively mute it.

but then, i'm JUST NOW beginning to "get" ohm's law and grok how all this stuff works, and the math isn't as scary as i thought.

i appreciate the research links from dino, the pic from amptramp, and of course anything mark says always leads me to greater underrstandings than i thought possible.

it was weird... i thought optocoupler and bypass would get me a lot more hits than it did, mostly all i got was every other practical use for them

i am gonna fall down them rabbit holes and see what i come up with.

so am i right then to think my idea COULD work to trip relays remotely?

i know its more parts and more money... but the idea of it seems worth at least monkeying with.....

and of course, the idea of passing signal with light came to mind, or using infrared versions of the optocouplers and stuff.

originally i thought the kind that's basically an led and a photo transistor in one package would be interesting for a fuzz or something... power the led, light hits base on the q, and boom, current flows...  could you still pass a signal thru it tho, from c to e? or am i being brain dead again.

watching some videos on youtube that were completely unrelated to stompboxes just made me curious if this kind of tech could be useful.

i mean, some circuits, even with proper pulldown resistors can still "pop".... or like, if you're switching something INSIDE the circuit proper, maybe it would cause less pops, like my silly 2399 mod to switch the input to the jellybean off and on and leave the dry side always connected to get tails.

that can make it pop if the caps aren't charged yet in the circuit... usually the first time you bypass, it will "pop pop pop" slightly, but after that the switching is silent.

if i could do that with an opto instead of a mechanical switch, i thought it may be a useful fudge for that kind of situation, or similar.

and extra added bonus, its just nice to talk a little smack with the boys once in a while, too

[pinkjimiphoton]

Bro, didn't you already go down this rabbit hole?
https://www.diystompboxes.com/smfforum/index.php?topic=117272.0

hahahahahah holy cow, dino, i didn't remember til i saw it just now... lol. nothing new under the sun!!! 

[Toy Sun]

Also into the idea of remote switching, no audio going between the actual switch and the relay. In one of the above posts, it was implied that an optocoupler is needed for that. Did I get that right? My idea has always been to use one of the many relay bypass systems available, either someone's PCB or roll my own and just run a set of long wires to the switch.

Is that problematic?

Thanks,
John

[rankot]

I've been going through similar topic in the search of speaker protection circuits. Finally settled on this one, built it, but still didn't have time to test it. In case you can use this, here's the schematic - it combines delay circuit with NE555 and DC sense with optocoupler switching MOSFETS, to cut the signal for speakers:



Maybe you can use something similar for bypass? If you want, I can post spice code here.

I sneaked those circuits posted above, they are all quite simple, but don't provide any switching delay, which could be handy. Maybe adding transistor driver for opto, together with capacitor controlled delay could provide that?

[pinkjimiphoton]

Also into the idea of remote switching, no audio going between the actual switch and the relay. In one of the above posts, it was implied that an optocoupler is needed for that. Did I get that right? My idea has always been to use one of the many relay bypass systems available, either someone's PCB or roll my own and just run a set of long wires to the switch.

Is that problematic?

Thanks,
John

hi john,
you don't NEED one. i'm just currently kinda fascinated by the idea of using light to control stuff... seriously considering trying a fiber optic rig between my pedalboard and amp, i was surprised at how easy it appears to be to do that.

for all intents, you send your signal to a 386, have the 386 power an led, and use the led to drive the fiberoptics. no noise!

dunno how practical it will be, but...

and here's a thing on optos, and what piqued my curiousity

Ranko, would love to see more of what you did, too! looks cool!
knowledge is power, bro, so always interested in.... well, everything!

[Toy Sun]

I also love controlling things with light. The fiber optic idea sounds cool. Long runs, no noise, and I assume cheap cables easy to replace (DIY Toslink?).
My one and only patent is for a device that communicates with a screen through light. The challenge was in early iPad days and getting Apple's approval to use the proprietary connector would take 6 months. The team wanted to be first to market. I came up with the dead-simple photoresistors sitting on the screen. Worked great, no connection needed.
There is also a reason why IR remotes are popular: no FCC/radio issues.

[mdcmdcmdc]

Just for reference/so it's in the thread, here's the voodoo labs optocoupler bypass schem: