I’ve made the adaptor boards, I found that if I solder the boards upside down to normal 6 of the pins including power line up with the Seeed XIAO RP2040.
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That’s a very neat solution!
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Thanks, I only have to change 4 GPIO pins in the code now for this device to test it. But I really should be concentrating on my Polysynth build rather than this, but I wanted a distraction to let my mind refocus.
Update: New chips are in after a quick code change and definitions of the pins for easier identification. Took me a while to get the Arduino IDE libs into a state where the code would compile for the zero, eventually cludged it into a working state.
Just been breadboarding the mux/demux to give 32 analogue channels in and out for CV control of this synth. Seems I’ve been doing things all wrong. I was enabling the output of the 4067 before setting the DAC voltage, this gave rise to a few glitches in the matrix. So I’ve coded this DEMUX to change voltage and then enable the demux output for a short while to charge the sample and hold capacitor before disabling the DEMUX again and moving onto the next output. Now as the Teensy 3.6 has dual DACs it seemed sensible to write to both channels at the same time which means I can reduce the passes of the DEMUX from 32 to 16 to write all 32 channels. Also the DEMUX and mux chips can be powered from 5v rather than 3.3v to allow full voltage swing, they still switch happily with 3.3v select lines. This has improved performance a lot. I noticed this on some polysynths that the mux voltage is slightly higher than the pot swing for example in the prophet 600 the mux regulator voltage goes to 5.6v but the pots are 0-5v. Just a tip for people.
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I ran some tests on another test bed with a Teensy 4.1 and external SPI DACs and 4051 for the DEMUX chips. I can duplicate the results of a smooth sample and hold output for 32 channels. Again I’m using dual channel DACs (mcp4922 with an external 2.5v reference) so I can write 32 channels in 16 passes. Currently it’s set up for 32 single passes but it works.
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Finished the upgrade to make the synth programmable, the waves are now selectable with a pot. Every value is stored in memory for recall of 999 programs.
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AliExpress just search proto board 20*30
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Cheers. Much appreciated.