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Seeking documentation for INTERMIDI Encoder board, circa 1980

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  • Seeking documentation for INTERMIDI Encoder board, circa 1980

    The piano keyer on my organ was connected, by a previous owner, to an INTERMIDI encoder board. I haven't been able to find much information on this board, its configuration or settings. I wonder if anyone here might have some information.
    Eric Mack
    www.ThisOld340.com
    Rodgers 340 S/N 34341
    Los Angeles, CA

  • #2
    Hi Eric,

    I couldn't find any Intermidi information on the Internet when I searched last September. I scored a Rodgers Trio 321C last year and when I opened up the back I found that the Solo keyboard had been hooked up to a some Intermidi boards, very likely the same as yours.

    According to my notes, there are three boards. One is an "MMI 1.20 Controller" with a Z-80, EPROM, and SRAM. It's obviously designed to produce a MIDI Out data stream over a good old 5-pin DIN connector. I have no idea if it works (EPROMs don't remember forever) and I'd have to buy a USB MIDI adapter to use it, so I'll most likely give it away some day. That's the one you're probably most interested in. I don't have any documentation, but if it works I could probably figure out what it's doing. I would guess that it's only producing "keep alive" messages along with Note ON/OFF messages. I didn't take a close look at the board to see if it had DIP switches to configure channel # and/or velocity values. I would expect those to be the only configurable parameters.

    The other two boards "KMI-1.10" are obviously the keyboard encoders. Each board has eight NEC 2501 ICs. I think they're the same as a CEL PC2501 quad photocoupler which has a downloadble data sheet. I'm guessing that each board encodes 32 keys as a 4x8 keyboard matrix. Using photocouplers is a nice (but pricey) way to deal with the +12V key switches on the Trio so there's no danger to the 5V logic on the Intermidi boards.

    Some day (I hope this year) I'm going to add home-brew VPO to my Trio, and having the Solo already wired up will save some time. My plan is to reverse-engineer the matrix boards to see how they're wired up. That's easy with a 1980 board with 0.1" components and connectors. Then I'm going to use one of my ST Discovery boards to scan the keyboards and stops to produce a USB MIDI stream. Scanning the Trio stops is another fun project :-)
    Last edited by johnbeetem; 03-18-2019, 08:45 AM.

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    • #3
      Hi John, when I got my Rodgers 340 (similar in architecture to your Trio) the previous owner had disconnected the piano keyer (Only) and routed that to the Intermidi. That provides MIDI out for the PIANO only. From there, he installed the motherboard from a digital keyboard to provide the wave samples. That motherboard was modified to provide 16 switches on the front of the organ for other instruments that could be played from the piano stop on the organ. (e.g. xylophone, clarinet, etc. ) it was a clever solution. I have since removed the motherboard and all of its switches. In its place I put something similar. Works great. And, I'm pleased to say that 40 years later, the Intermidi continues to work fine, too. I plan to keep it until I install Artisan. Meanwhile, I was curious to find any documentation.

      UPDATE: As I typed this, I thought of one other place to check. The Rodgers Theater Organ Users group on Yahoo. I have an archive of it, so I searched and found documentation and notes on Trio interfacing! I'll scan and post. If you are not already in RTOU, it's inactive but rich with info. I will scan and share.
      Eric Mack
      www.ThisOld340.com
      Rodgers 340 S/N 34341
      Los Angeles, CA

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      • Eric Mack
        Eric Mack commented
        Editing a comment
        Also, be sure to see the posts from the John who has been sharing his Arduino Encoder/Decoder/Stop plans and code. For example: see: https://organforum.com/forums/forum/...dule-version-2

      • johnbeetem
        johnbeetem commented
        Editing a comment
        That's a very cute customization. My Trio's Piano stop is pretty bad -- it sort of sounds like a banjo. The harpsichord is awful. On the other hand, the chimes are very pretty. My Trio also has a Glockenspiel -- 30 bars of real metal with magnetic strikers. Never needs tuning!

    • #4
      OK, I had forgotten I had access to an archive of the inactive Rodgers Theater Organ Users on Yahoo. (I use PG Offline to archive those groups before Yahoo destroys what is left of them). Anyway, in the files section, I found these Intermidi files plus someone's drawings of a Trio conversion.It appears that Intermidi system would do 3 manuals plus pedals. Intermidi - Installation notes.pdf Intermidi - Programming pistons.pdf Intermidi - Block diagram and programming.pdf Intermidi - Trio schematic.pdf

      Since the files are there, there must also be a discussion around that topic, so that would be something to look at. I have no immediate need. The intermidi works fine for the piano. I hope this information is helpful.
      Eric Mack
      www.ThisOld340.com
      Rodgers 340 S/N 34341
      Los Angeles, CA

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