Spin Semiconductor

Say you want your pots for other parameters, could you use something like electricdruid's fantastic TAPLFO into a pot input or even RADC? I assume so, but couldn't find any mention when searching.


Likewise, I assume people have already used a PIC to process the pots into CV and used that to make presets? With enough pins that would allow a preset to constitute three knob settings AND a program selection, and furthermore allow a pot to be used to select the program (just with a simple 3 bit ADC!)

Thirdly, if I already have an EEPROM programmer, could I make my own crude dev board that way without the USB bits? I'd like to get the real thing eventually, but I'm in that awkward "just graduated" position of not knowing what my financial situation is actually like until I know what I'm doing next!

Hides-His-Eyes wrote:Say you want your pots for other parameters, could you use something like electricdruid's fantastic TAPLFO into a pot input or even RADC? I assume so, but couldn't find any mention when searching.

People have run LFOs into the pot inputs but keep in mind the pot inputs are filtered to remove jitter and have a long time constant.

Hides-His-Eyes wrote: Likewise, I assume people have already used a PIC to process the pots into CV and used that to make presets? With enough pins that would allow a preset to constitute three knob settings AND a program selection, and furthermore allow a pot to be used to select the program (just with a simple 3 bit ADC!)

I've heard of people doing this but have not seen a schematic myself to point you at.

Hides-His-Eyes wrote: Thirdly, if I already have an EEPROM programmer, could I make my own crude dev board that way without the USB bits? I'd like to get the real thing eventually, but I'm in that awkward "just graduated" position of not knowing what my financial situation is actually like until I know what I'm doing next!

Yes, this is easy if you have a programmer already. Just d/l SpinAsm and when you make a project check the box to make a hex file and it will produce an Intel HEX file that just about every programmer is able to read and use to program a 24LC32A. A lot of DIY people and small pedal companies are doing this because they already have a programmer, they just put a socket in the project so they can easily swap eeproms as they develop their programs.

What's the time constant on the pot input? 10s, 100s of milliseconds? Will the spare audio input struggle with DC in any way?

I'll have a think about the PIC bit then. If I can get something like that working I'd love to contribute.

I think a "dev pedal" is easily done then. How critical is using two layers if you use the 15p cap? (Would 22p be ok there?) I don't mind doing proper two layer layouts but if I only want one of them I might see if someone would just etch it for me.

Hides-His-Eyes wrote:What's the time constant on the pot input? 10s, 100s of milliseconds? Will the spare audio input struggle with DC in any way?

POT time constant is about 100mS. Audio inputs only want an AC signal so you really don't want to run DC into it.

Hides-His-Eyes wrote: I'll have a think about the PIC bit then. If I can get something like that working I'd love to contribute.

That would be great, really nice to see a design using the PIC to store presets.

Hides-His-Eyes wrote: I think a "dev pedal" is easily done then. How critical is using two layers if you use the 15p cap? (Would 22p be ok there?) I don't mind doing proper two layer layouts but if I only want one of them I might see if someone would just etch it for me.

Well, 2 layer always helps with routing and keeping things quiet. 22pf for the cap on the resonator is probably fine, this is a non-critical value. We discovered due to the high gain in the XTAL pads that some resonators would go into a high harmonic (someone with more knowledge about how crystals are cut may want to explain the details here). The cap suppresses this so you don't want a large cap on the pin but moving from 15pf to 22pf I think is OK.

We're using 22pF for production and it's OK.