Controlling ditto looper with micro-controller

[spoitras]

Hello,
I've replaced the footswtich on my ditto looper with a mini jack. So far, if I plug in a patch cable and short the tip to ground, I get the behaviour I normally expect from the footswitch on this pedal.



To control this with a micro-controller, I can think of three ways to proceed by essentially replacing the original switch with either:

• an opto-isolator ic
• a relay
• an analog switch ic

Am I correct to assume these three options would function equally well? Would any of them be preferable? I would rather not use a relay if I can help it to keep the (mechanical) noise to a minimum... I'm mostly leaning towards the analog switch IC since I've used them before and I have a few on hand.

Any thoughts?

[highwater]

For the switch IC, there are two main concerns that I can think of:

1) Does it/can it leak DC into the signal path? If it does, you might have problems. If the signal pins need to be biased to a particular DC voltage, then it probably won't work at all.
2) What's the on resistance? Find a resistor near that value and connect it between tip and ground - if it still works, you should be fine with the IC.

[spoitras]

For the switch IC, there are two main concerns that I can think of:

1) Does it/can it leak DC into the signal path? If it does, you might have problems. If the signal pins need to be biased to a particular DC voltage, then it probably won't work at all.
2) What's the on resistance? Find a resistor near that value and connect it between tip and ground - if it still works, you should be fine with the IC.

Thanks, those are great points to consider.

I went for an opto-isolator in the end because I liked having all the control circuity in the pedal. This way, I can send 5v triggers from a micro-controller pedal or from my modular synth and the ditto will respond to both equally well. Works well on the breadboard, I'll try to solder it together this week.

[spoitras]

Here's a video of the completed mod:
https://youtu.be/sDWQqti_hbA

[ElectricDruid]

I know you've completed this, but if the original pedal just uses a short-to-ground, that suggests to me that the switch is connected to a micro controller input. These typically have internal pull-ups, so the easiest way to add a switch is a short-to-ground. You can use an NPN transistor to short the input to ground in the same way - either instead, or in parallel with the switch. It doesn't need a relay. Essentially this is the same as your opto-isolator, except without the isolation!! If you're connecting it to a modular synth, you'd need a 10K to the tranny's base and a diode to ground to protect the tranny against negative inputs.

HTH,
Tom

[spoitras]

You can use an NPN transistor to short the input to ground in the same way - either instead, or in parallel with the switch.

Thanks Tom! That's certainly an elegant solution.

Am I wrong to be wary of doing without isolation in this case?

Sylvain

[ElectricDruid]

You can use an NPN transistor to short the input to ground in the same way - either instead, or in parallel with the switch.

Thanks Tom! That's certainly an elegant solution.

Am I wrong to be wary of doing without isolation in this case?

Sylvain

That's up to you, I guess. I've used the transistor solution on modular gear plenty of times, and I've tested whacking it with +20V signals and it survives that, so that was good enough for me. The opto-isolation keeps the grounds separate, which might sometimes be an advantage, but aside from that, I don't see any particular benefit to it.

Tom