SID Organ

Behold the unholy marriage between an old wrecked reed organ and a SID chip.

Features:

  • 62 keys, monophonic CV/SID or polyphonic Midi. No touch sense.
  • Adjustable keyboard split high/low.
  • Individual envelope and arpeggio and glissando for each keyboard split.
  • 2 LFOs. Sine only so far.
  • 4 Control rods assignable to a lot of different functions and parameters.
  • Built in MOS6581 SID chip. You know. 3 channels triangle/saw/square/noise and all.
  • 4 0-10V CV out for Euro Rack module control.
  • 2 gate inn/out  for Euro Rack control and external arpeggio sync.
  • 10 save slots for settings (pre-named after C64 games from A to J)
  • some stuff i can’t recall…

I found the old reed organ in a really sorry state after at least a year outdoors in the Norwegian rain. It was already on its way to the trash yard, and the keyboard was so swelled it looked like a sine wave. I knocked it apart and kept only the keyboard section.

I have mounted pushbuttons and springs under each key. Instead of a keyboard grid I have used PCF8574 expansion boards (which I happened to have a pile of) making the whole keyboard I2C interfaced. An Arduino Mega takes it from there.

The sound is generated from a MOS6581 SID chip controlled straight from the Arduino Mega, but it can also 1V/octave control external oscillators trough one of the four CV outputs. I have made room and power for a few eurorack modules at the right side. At the moment I only use a reverb unit which I control with CV out patched to one of the Sound Rods, and patch the SID audio output trough this. Yes, and a home made eurorack master clock so I can sync arpeggio with my Ditto guitar looper.

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The old sound control rods are connected to potentiometers and sent to the AIs on the Mega. The transmission only moves the potentiometer a few degrees so the voltage difference is quite small. I have compensated somewhat for that by changing the analog reference voltage as low as possible so I don’t waste to much resolution.

20171216_125539.jpg

I have used one of the tiny 128×64 oled displays from ebay, together with an encoder, to allow serious menu diving. There is A LOT of settings available so far, so this unfortunately necessary. I would really want a bigger display, but that would require more memory for the display library and I’m already dangerously low on RAM.

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On the software side I had some challenges with the multi-level menu system and the lack of memory, forcing me to learn more about pointers. Which is a good thing I guess. I have made my own Arduino libraries both for the menu system and the SID, only the latter anywhere near clean enough to share with you guys.

20171216_125352

Problems so far:

  • The SID and CV-out circuits is a breadboarded rats nest and not trustworthy.
  • The Mega is almost out of memory. The oled library takes a lot. The menus take the rest.
  • The Mega is to slow to allow smooth LFO/Envelope/Appergio/Glissando processing together with menu operation. Glitching occurs and resources are maxed out. Okay, maybe with tons of optimization but ain’t Nobody Got Time for That!
  • The filter of the SID chip does not work. Yes they are bought on Ebay.
  • The +/-12V power supply made from scrap transformers gets dangerously hot. Also it is a bit hummy which you might notice on the video. I have used it for hours with no problem but I am afraid it will burn down the house if I forget to switch it off.

Future plans:

  • Replacing the Mega with a Teensy to satisfy my need for speed and memory. I am not planning on any audio processing in the teensy, only menus and control signals.
  • Getting a bigger display. Menu diving on the tiny oLed is mildly cumbersome.
  • Designing and printing some PCBs for the SID and the CV out,  trough Dirty PCBs. Both cards will be I2C controllable to save pins and to avoid level shifting a million pins from 3V3 to 5V if I move to teensy.
  • Building a new power supply. From new parts.

 

Gotten this far? Maybe add me on Instagram: https://www.instagram.com/tinkartank

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12 responses to “SID Organ

  1. Pingback: I2C controllable MOS6581 card | neo-norwegian experiments in art and technology

  2. Pingback: I2C controllable CV output card | neo-norwegian experiments in art and technology

  3. Pingback: SID Organ Pulls Out All the Stops | Hackaday

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  5. Pingback: SID Organ Pulls Out All the Stops – High Tech Newz

  6. Pingback: SID Organ Pulls Out All the Stops | Premium Blog! | Development code, Android, Ios anh Tranning IT

  7. Pingback: Arduino Blog » Playing chiptunes on an old reed organ with Arduino Mega

  8. Pingback: Playing chiptunes on an old reed organ with Arduino – Arduino Boards News

  9. Pingback: Playing chiptunes on an old reed organ with Arduino |

  10. This is superb. Would you be interested in letting Hackspace magazine feature it in our Top Projects pages? We’d need 2 or 3 photos, plus around 100 words giving an outline of the project.

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