Another Arduino project from HAGIWO
"My 8th arduino synth project.
Gakken SX-150 type low pass filter VCF with arduino nano.
It operate only 5V ( to 12V ) , no need negative voltage.
Sallen-key type filter is used for KORG MS-20.
Gakken SX-150 is Japanese low cost desktop synthesizer.
Its VCF circuit is very simple and operation with AA battery.
My VCF has distortion and resonance.
It’s not electrically beautiful.
But it helps to make a fat synth bass."
These are brilliantly simple builds. @Dud you should invite him here.
Are you (anyone) building these?
I wrote a little thing on his channel 
no build yet for me, but for the next case surely the Generative sequencer !!!
Not having watched this, I’m confused as to why anyone would need an Arduino to make a Sallen-Key filter?
I’ve looked a the design and wondered why he is using an arduino. The arduino and ADC could be replaced by maybe one potentiometer and keep everything analog. That would simplify the circuit a lot.
[Edit] On his blog he states that he wants to learn how to program. Maybe that is why in all of his designs there is at least one arduino even if circuit wise it does not make too much sense to include one.
I think he’s doing an excellent job exploring the use of mcu in modules. There are indeed many ways to filter with many results. Why not?
But I mean, what’s he using the Arduino for? What function does it play?
I suppose that was inevitable.
I’ll get my coat.
(Photo credit Illmind on Soundcloud)
Does it have to do something ?
Read just the CPC472 paragraph… 
Oh I think I remember that vaguely. I think the issue was that the ñ character was missing from many keyboards sold into the Spanish market at the time.
And the tax for computers with up to 64KB of memory.
So just add a 8KB chip to get over the limit, which isn’t even connected to the rest of the computer…
It appears all the Arduino is doing is reading two CVs, summing them, and sending the sum to a DAC.
Which could be done with a single op amp and a resistor, instead of an Arduino, a DAC, and the pin protection devices.
I mean, it works, but it’s not a design I’d ever want to emulate. If it’s an $8 module the way he did it, it must be about $2 the other way.
You work with what you got.
Suffer what have
and suck the marrow from it all.
Chew it all fine,
swallow all that juice 'n brine
And then you spit.
Hey! what you lookin at?
Sam made a can drum machine … is it the best way?
Dud’s dial trigger …
Bottom line is its not what you do but the way that you do it.
Enjoy all these creations. Whether they make sense or no.
Maybe he’s doing it to avoid using an opamp and the -12v … since his splash screen calls out that it doesn’t use -12v
Why speculate if one can ask?
Jos Bouten:
I was wondering why you are using an arduino and an ADC when choosing a voltage for the VCF could also be done with a potentiometer or some small analog cuircuit?
HAGIWO modular synthesizer channel:
The reason for using arduino is to step down from 12V to 5V, reduce analog circuit tuning man-hours, and turn on the LED. arduino has no important role as a VCF.
Although it is not an Arduino, I made a VCF PCB using Coolaudio’s V2044IC designed by HAGIWO.
It’s simple but works effectively and I love it.