Logic chip, flip flop, or relay?

[Matthew Sanford]

So, almost done with home repairs, and wanting to get back to it. I've been playing with a PT Wobble type thing, but want to switch between a StompFLO and One Shot. 4 CVs and the LFO to switch. First I was thinking NPNs instead of FETs in an extended flip flop, was worried about the voltage level changing (or would common base work?), then thinking a 74hc157, maybe flipping relays...?

I figured relays would keep the signals the same better than the others, but haven't had time to play with any of it...on the other hand,





I'm almost done with the house, so it's just been running round my head. Any pros or cons to each method? I'm figuring the 157/relay way would be lowest part count.

[ElectricDruid]

You can probably parallel up the CVs on both chips. Use one set of controls, but feed the pot wiper CV output to both chip's inputs. You might need 1K series resistors to each input, but I'd try it without first and see if it's ok.

Like that, you'd only have to switch between the two outputs, so you could just use a simple switch.

[Matthew Sanford]

Interesting. I figured to do that with the tap/trigger to a momentary but thought the others would interact. I'll try it, hopefully this weekend. Thanks!

[ElectricDruid]

Interesting. I figured to do that with the tap/trigger to a momentary but thought the others would interact. I'll try it, hopefully this weekend. Thanks!

"Interact" how? The trouble will be that the best setting for one of the chips probably won't be the best setting for the other chip. So you might still want two sets of controls, so you can fine-tune each one and then jump between the two sounds.
But in principle, there's no problem with paralleling up several chips. I don't know of examples with these two exactly, but people have paralleled up 5,6, or 8 chips of the various Env Gen designs I've done for polysynth projects and there haven't been any problems.

[Matthew Sanford]

Good to know, I think I'll try just the PDM switch first. I do think I'll want separate controls...though I was thinking to route one or the other to the pots, which means same issue, and 8 pots just feels like too much...any tricks to have it remember settings? I'm guessing digital pots or something.

I do want to route whichever signal is hitting the closed switch to be able to route to an out jack, for CV control on something else. This is all great food for thought though, have to (hopefully) make time to breadboard this weekend

Thanks again!

[ElectricDruid]

any tricks to have it remember settings? I'm guessing digital pots or something.

Well, the chips are expecting a 0-5V CV, so anything that produces that is fine. That means a DAC, digital pots, an Arduino's PWM outputs (with a bit of filtering), whatever. It's all shouting "PROCESSORS!" at me at that point though - remembering settings is a job for microprocessors and code, in whatever form you like best.

[Matthew Sanford]

Hmmm...wondering if I figure the voltage drop from in to out on the 157, if I can feed one from the pots, adjust it after, then would it hold the voltage? Or...maybe look for a Schmitt trigger one, then it should hold and I can switch the after parts. Something I need to learn on, but that's what holds its output state steady, regardless of input changes, yea?

Ok, thank you on this, I'll riddle through a bit more...