hi
trying to trigger an external looper pedal using arduino.
looking for the easiest way to send 3.3V coming from looper into arduino GND. This has to succed for a split second in order to trigger the looper via arduino.
is there an alternative to BJT tramsistors? as there is no need for a continuous circuit. just a quick "draw" of 3.3V.
Thank you!
hi
my looper pedal is triggered by a footswitch that once pushed down releases 3.3V into ground.
my intention is to trigger this switch via arduino.
what is the best solution for this?
Can you add more information please? Maybe even add a schematic?
From what I understand right now, there is a connection on your pedal, that while not pushed, sees a logic high. When pushed the connections goes low.
Just connect your arduino and do something like
// triggered
digitalwrite(arbitraryPin, LOW);
// not triggered
digitalwrite(arbitraryPin, HIGH);
and find out whether you just a need a short pulse or if you need to set the connection low during the entire trigger time.
thanks for the quick reply!
you are right. when the footswitch connection is pushed, a short pulse of 3.3V is sent to ground. see attached pic.
just wondering what happens when two parallel unequal voltages meet up, namely the
arduino logic high = 5V
looper logic high = 3.3V
will the arduino create a current inside the looper? are there any risks involved?
Oh my god, I'm so sorry that I completely missed (hate the strict no edit limit < 100 posts). Fortunately I was still waiting on further confirmation from you anyway.
There are logic shifters designed for that purpose: they take the logic high from the arduino and convert it to 3.3 V. See https://www.sparkfun.com/products/12009
I stand corrected here but I'm pretty sure the footswitch and the arduino circuit need to share a common ground too.
OK now, it seems there was no answer to your first post so you tried again. I have asked for a moderator to combine them.
So, you have a footswitch jack that "sees" 3.3 V, positive to its ground (which must then connected to your ground). This is obviously a logic input to some circuitry with a pull-up inside.
Your original post seemed to have an aversion to using a transistor. I cannot imagine why, as a transistor is the answer. Perhaps that is why no-one thought it wise to reply. I didn't at the time, but I do get rather busy ...
Now the "logic shifter" chuckyx suggests could be used purely for its FET which is a "better transistor". That would be safer than using an Arduino pin written LOW and switched between INPUT (open circuit) and OUTPUT (grounded) because that leads to concerns about one part being switched off while the other is still on. If they both had the same power rail that would be just fine. 
The trouble with the logic shifter is that it has extra components which would get in the way.
Paul__B:
The trouble with the logic shifter is that it has extra components which would get in the way.
Do you care to elaborate what exactly get's in the way? I'm still learning myself and I have some of these lying around in case I need to work with a logic on a different voltage level. Thanks!
paul. thank you for the extensive answer!
your solution to switch btw low input and low output seems to be the perfect solution.if I understand correctly,
LOW INPUT = Arduino as a voltmeter (open circuit)
LOW OUTPUT = grounded circuit
Perfect because it involves no mismatched voltages, hence no risks. No logic shifters either.
I don't understand the concerns about one part being switched off while the other is still on.
chuckyx:
Do you care to elaborate what exactly get's in the way? I'm still learning myself and I have some of these lying around in case I need to work with a logic on a different voltage level. Thanks!
Well, here is the circuit for a common dual level shifter:
You basically want to use the FET just as a transistor, so you could tie one of the left hand terminals to ground and use the "+3.3V" terminal to control the gate, with the right hand terminal as the drain to switch your device. Now you have other FET tied in with the resistors.
It almost certainly will not cause a problem, but adds some parasitic capacitance, no actual concern in this application. The alternative is to tie everything together in parallel which - apart from that parasitic capacitance - would work just fine except for this module which includes a regulator.
It still gets a bit strange if you are using a four way module or this: 
orinocopaul:
I don't understand the concerns about one part being switched off while the other is still on.
Well, if the Arduino is switched off while the looper pedal is on, the Arduino will pull the connection continuously LOW. Simple as that. A transistor or FET will not cause that to happen.
thank you, paul!
for the convenience of powering both the arduino and the looper wih a single usb cable, I have decided for a common rail.
however. still haven't figured out how to step up the 5V of the USB to the 6V (200 mA) of the looper. before or after arduino... etc
I don't follow. Why do you now want to power the looper pedal from the Arduino. Does it not have its own power source?
to trigger itself, the looper switch is sending a pulse of 3.3V into GND. I am following one of your previous suggestions to switch pins btw
LOW INPUT = Arduino as a voltmeter (open circuit)
LOW OUTPUT = grounded circuit
current is flowing in one direction only, so no need for logic shifters or FET, as the arduino is always on LOW (for safety reasons thought about using a one direction diode only)
still, as you pointed out, if the Arduino is switched off while the looper pedal is on, the Arduino will pull the connection continuously LOW. this led me to thw idea of powering both of them from the usb cable, as it also adds the extra benefit of the one cable connection. the only problem is that the looper needs 6V (200 mA)
Perhaps you should explain how - exactly; using what actual components or units - each device is presently powered?
the looper originally takes 4 c type batteries but I modified it to
7,2V NP-F batteries + buck converter (6V)
currently have an arduino uno r3, but waiting for the pro micro 5v 16MHz. both are usb powered
figured I could ditch the buck conveter and power everything via usb
Yes, but you haven't explained what USB power source you would use. "USB" is not a battery or transformer.
You could use another buck converter to produce the 5 V from your 7.2, presuming you actually want it all battery powered.
imdeed sorry.
arduino will be bus powered over usb. 5v from computer. no more batteries in this case.
so the usb will ideally carry both
5V for arduino and looper
midi data for the arduino
Yes, sounds as if you need to swap to a boost converter then.
Note however that since a "looper pedal" is presumably an audio device, you may need careful design and bypassing to keep noise out of the audio.
On the other hand, if you are already using a switchmode "buck" regulator, the problem must already be solved.
dear paul
thanks a lot for your support!
put up everything together and everything worked out fine, except for
1
btw 3.3V looper and 5V arduino current is flowing in one direction, so no need for logic converters. only wanted to add a diode in-between, but couldn't find a Schottky one that doesn't drop the voltage below the 3V threshold. not a big concern at the moment.
2
you were right. now that the looper is usb bus powered, there's a terrible hiss coming out. the only workaround I found to be working is plugging the looper's original ac adapter, which makes the 6V redundant, and pushes 9V AC through an in-built rectifier instead. this kills the hiss almost completely.
have not researched the problem yet, but would appreciate some tips on issue no 2
orinocopaul:
have not researched the problem yet, but would appreciate some tips on issue no 2
You may just have to live with it. Hiss removal would involve complex matters of how it is wired, extra inductors and such. Not easy to figure without the things in front of me!
was also thinking about inductors. humbuckers. ground splitting re-amp boxes etc. also looking into other bus powered audio devices (such as DACs).
however, the initial problem - logic converters - has beem solved long time ago 
thanks a lot for the crucial extra support!
and let's call it [SOLVED] for now
