Hagiwo Sync VCO mods

Carrying on with the search for an interesting DCO, I was looking at Hagiwos $25 Hard/Soft Sync VCO which is based around an UNO R4, something which is hard to obtain and expensive and quite large unless you can get the Flint format one. Anyway it uses the onboard DAC to generate 4 different waves, saw, square, triangle and sine selectable with a pot. You then have some Freq and Sync controls, and octave selection and a volt/octave CV input and a Sync input which seems to require an LFO to activate the sync sounds unless you use the sync control.

I took this and ported it to a waveshare Zero RP040 board and an 8 channel16 bit DAC. First thing to do was get the DAC to output a wave and test the functionality. Took a while but I got a waveform, then I took the resolution of the original waveforms from 10 bits to 14bits to smooth out the edges of the waves. This again worked well and the waves were smooth. Finally I wanted each wave to appear individually on a channel of the DAC, this again took all my tiny brain power to achieve, but it got me there.

It has MIDI now and the octave and hard/soft sync is under CV control.

Next is to take away the volt/octave and replace it with MIDI notes and add glide. Hopefully it will make a nice oscillator as the basis for the next synth.


This is really very good and could be very useful indeed. I would love to know more about how you incorporated the DAC and simultaneously generated waves. Will this be added to your GitHub?

It’s still a WIP, I’m not a 100% sure of the functionality of the original and without an R4 to test with I’m a bit stuck. I was messing with the midi notes yesterday and got it almost to play in tune, probably just need to adjust the caib variable to lock it in.

I will post it on GitHub, but it seems the DAC is just updated by an interrupt every 10mS or so from the wavetable.

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