Is there any reason that a backwards CV trigger would not fire? I used to think that it was a bad switch issue, but I have wired the forward and backward CV plugs directly into the arduino and only the forward trigger seems to work. The momentary switch works perfectly. The diodes are facing the correct direction and the plugs themselves seem fine.
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One thing to check is whether or not the software is looking for the backward gate on the pin that it is in fact wired to.
Forward and backward gates are wired the same way and handled the same way in software, so if one works and the other doesn’t, a software/hardware mismatch like that is all I can think of.
Do the gate inputs have pulldown resistors, located closer than the diodes to the Arduino?
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Yes, pulldown resistors are all on the socket side (where the diodes are) as opposed to the arduino side.
I notice now that the “L” led on the nano flashes in sync with the back pulses. Not sure if that helps at all.
Pulldown resistors should be on the Arduino side of the diodes.
Hmm. Back is supposed to be connected to pin 13, and pin 13 connects to the LED. So it sounds like the back gate is getting to the Arduino. Software (if it’s the same as the posted version) looks for the back gate on pin 13. So it seems like everything’s as it should be.
None of the other signals make that led light up. Its a real head scratcher.
The LED is connected to pin 13 which is what the Back gate uses.
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Unrelated question, but I see a lot of people adding op-amp buffers to their inputs/outputs to protect modules. Is that something worth adding to the circuit or does the Arduino have that covered?
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Also I saw @analogoutput recommend skipping the 5V regulator that Sam added because it would prevent the Arduino from being able to output 5V. Why not use a 9 or 10V regulator instead so Vin stays between the 7-12V that’s recommended for the Nano?
Did I? I used one in my build. But I connected it to the 5V pin, not the VIN pin, bypassing the Arduino’s regulator. The idea being that it can supply more current than the Arduino’s regulator can, though maybe it doesn’t need to. Seemed like cheap insurance.
You could use a 10V regulator on the VIN pin but is there any advantage in running 12V through two consecutive regulators versus just 12V to VIN or to an external 5V regulator to the 5V pin?
Op amp as protection? Seems odd to me. Protection against what? A series resistor will limit current, and if you want to limit voltage a couple of Schottkys will do that. The Arduino has protection diodes on its pins but you can argue it’s better to burn out off-board diodes than on-board ones.
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Really? I thought the 5V pin was meant to act as an output. It doesn’t seem like you’d need to supply more current. I know you need enough to turn on the signal LEDs, and the current flowing to the CV outputs aren’t that important. Wouldn’t supplying more current just cause it to consume more power than needed?
As for the regulator I figured since the max Vin recommended is 12V I’d air on the safe side and supply with something a little lower like 10V. Not sure if this is a great idea though, it’s just something that came to mind.
From what I’ve seen it’s just a way to avoid having to worry about impedance matching between modules. Sounds like I need to do more research into this.
Yeah, the on board regulator’s probably got enough current capability. Like I said, I just figured the external reg was cheap insurance. The 5V pin outputs 5V when you supply 7–12V to the VIN pin, but that just means it’s connected to the regulator output — and you can just as well connect it to the output of an external regulator to input 5V. And having more current capability doesn’t mean it’s forcing more current down the Arduino’s throat. Just means it can supply more if the Arduino needs more.
I see various comments about the wisdom of using 12V on VIN. You’re right that it’s on the edge of the recommended range. But is double regulation the answer?
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Sure, that might be a good reason for buffering an input. I just wouldn’t think of that as “protection”.
Okay I forgot that you’d be increasing the current capability and not necessarily the amount of current actually consumed.
Yea there’s probably a better way of going about this than double regulation. Other than maybe making a voltage divider to step it down to 10V no other solutions come to mind.
So then are isolation buffers there to improve the efficiency of the circuit?? If that’s the case then it seems like the current limiting resistors/schottkky diode route you mentioned earlier would be a better solution.
It’s connected to the internal +5V rail. If you have a stable 5V, you can power the Nano that way:
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Thanks @analogoutput and @fredrik. This cleared up a lot of the misunderstandings I’ve been having.
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I know this is kind of a useless comment, but this project has been frustrating me for months.
I’ve finally got it all wired up and it doesn’t work properly. First only buttons 3, 4, 5, 6 were working (as in, triggering the LED to change). Now only buttons 1 & 2 work. Buttons 7 & 8 aren’t even picked up by the arduino. It used to go forward but skip around a little, now the switches are literally just showing random numbers in the serial monitor when I go to check on them.
Just feel really useless at this right now honestly. Haven’t even gotten to the point of trying the jacks because I can’t even get the LED to work correctly. I am not sure where i’m going wrong at all. It all seems to be wired up correctly, though there’s more bare wire than i’m comfortable with none of it is touching. In arduino it will pick up the first 6 buttons, but only do anything to the first 2 LED steps.
Frustrated 
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This project had me messed up for awhile too, don’t give up! If you see the numbers bouncing around in the serial monitor there’s a good chance you have “floating” pins. Did you make any changes to Sam’s schematic?
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