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Thread: MIDI convert Rodgers Asilomar 780 analogue sound w/t digital matrix console control

  1. #11
    mp Mezzo-Piano John Kinkennon's Avatar
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    Having converted a number of Rodgers and Allen consoles I have come to the conclusion that in most cases it has been easiest to gut as much of the dated electronics as possible in both cases. I don't attempt to reuse Rodgers serial (SPI) channel equipment except for the very latest examples. I convert any -12v keying or -16v SAMs voltages to 3.3v or 5v for keying and have modified -16v supplies to +16 with properly grounded chassis. I'm currently working with a coupler rail that used old 40x series CMOS chips and don't even want to guess what speed and mode they ran at and just how static prone they might be.

    Once the equipment is free of the old analog voltage polarities it's possible to use generic encoders and decoders to handle the keys and controls. Everything ends up being serial with conventional SPI channels or matrix, usually 8x8 or the Allen 11x6. With Allen stops I use some flexible 64 GPIO boards that are the slower I2C which is still good enough for the stops. Reuse as much existing wiring as possible and the project becomes manageable.

    I know I'm talking generalities here rather than Rodgers 770 specifics, but I get concerned when I see attempts to adjust to arbitrary voltages and polarities when it isn't necessary.

    EDIT: Of course I keep a 12v supply for Rodgers lamps but drive them via 5v circuits and open collector chips like the ULN2803A.

  2. #12
    Moderator jbird604's Avatar
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    Joel, you need to keep in mind the basic concept of the LED. It is not actually a "lamp" in the usual sense. An LED is a "light-emitting-diode" and as such it does not consume current like a light bulb or other common electrical device. It simply passes electricity the same way any other diode does, and in the process, it gives off some light, a mere byproduct of its passing current through.

    That is why an LED always REQUIRES that there be a resistor in the circuit in series with the LED. That is why the little circuit boards in the Rodgers have a resistor for each LED already mounted there. They are essential. If an LED is simply connected across a source of current, even if the voltage is very small, it will eventually burn up, probably VERY quickly. The resistor must be there to dissipate current, and the LED just acts like one of the conductors in the circuit, with the useful side-effect that it gives off light.

    So, whatever kind of interface you use, connect the driving voltage to the end of the resistor away from the LED and it will work perfectly and last for decades. I've never seen one of those LED's burn out on a Rodgers organ.

    We've gotten into some technical discussion here, but it still seems to me that SOMEBODY out there must make a simple, ready-to-install, drop-in adapter board that will accept the incoming "momentary contact" pulses from those Hall effect transistors, and will convert that to a "stop on" MIDI signal, and likewise provide 12 volts to light up the LEDs.
    John
    ----------
    Church: Allen MDS-45 with Allen MIDI-DIVISION-II expander
    Home: Allen Renaissance R-230 with expanded four-channel audio and MIDI-DIVISION-II
    Shop: Bunch of organs in varying conditions, some good, some not...
    Half of an incredible two-man organ service team -- servicing all the major digitals in Arkansas churches
    https://www.facebook.com/pages/Birds...97551893588434

  3. #13
    fff Fortississimo toodles's Avatar
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    Like all diodes, LEDs have a fixed voltage drop across them, though it's usually higher than your average signal diode. They are specified with a maximum forward current, and that's the purpose of the limiting resistor, which as JBird said, is necessary.

    Artisan has a 32 input/driver lighted piston board that could be used for encoding the Rodgers LED tabs, but it's for use with the Artisan MicroMIDI system. Not that the Artisan system isn't a fine way to go. I imagine that the Hall effect input operating on negative logic (0=true) could be handled in software. A quick email to Artisan or phone call ought to get an answer.

  4. #14
    ppp Pianississmo StevenJoelSpeirs's Avatar
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    I ordered everything I need to complete the project from Digi-Key.com. I'm using your suggestion for using the glass enclosed reed switches attaching then to the existing Hall Effect sensors with a single drop from a hot-glue-gun. My Classic organ works MCU only looks for 12 volts for note/on and could care less about the current, so I will cater to the Rodgers LED tabs needs. I will run the each individual LED in series with each Glass Reed Switch, ignoring everything on the stop-rail existing boards, only using the boards magnets and LEDS and using the Hall Effect Sensors as mounts for the reed switches. Since I will not use the existing circuitry, I will need to know the value of the individual resistors I need to use to keep from blowing the LEDS. Do you happen to know? I can read the values of the resistors populating the boards but they are involved in the matrix circularity. I found that lead 15 and 16 on the ribbon cable lights up all the LEDS on both stop rails. If I remove the voltage are reapply it every five seconds, it steps the stop-rails through the Rodgers factory default general piston settings that are remembered by the stop-rail matrix broads when the power is off. If I know (without error) what the individual resistors values will need to be for a single LED, I'm home free without blowing any LEDS.

    As far as the keyboards are concerned, I'm coming off the whiskers on the bottom of those boards, with individual wires (Cat-5 Ethernet cable) to the Molex connectors on top of MCU. The pistons I'm rewiring the same way. I am also rewiring the, toe tabs, and the pedal board reed switches with Ethernet cable to make everything uniform and more sturdy than the micro fine wire Rodgers used. The Rodgers thin wires will not hold onto the Molex connectors anyway, as they require for 24 gauge wire, and the MCU requires Molex connectors. So, that is that. My only problem now is the value of individual resistors needed for each individual LED. What do you think?

    Toodles, JBird just emailed me while I was replaying here, so I returned to edit this. Here is what he had to say...

    According to the Rodgers schematic, the series resistor for each stop tab LED is 470 ohms when used in a 12 volt circuit. These resistors would have yellow, violet, and brown bands, in that order. There is probably also a silver or gold band to indicate the tolerance, but it is not important. The resistors can be very low wattage. I'm sure 1/8 watt will do, as the LED's don't draw more than a few thousandths of a watt.

    Glad you found some help at Digi-Key. Those people are really nice. Keep up the good work!
    John
    Last edited by StevenJoelSpeirs; 05-17-2018 at 01:57 AM.
    Joel
    ----------
    My Organ:
    Rodgers 780 (Asilomar) 1983 #27 of 40 built. Console electronics gutted and replaced with the following;
    (1) Classic Organ Works MIDI Control Unit with optional General MIDI 2 Sound Module (Canada).
    (2) M-Audio MIDIsport 4x4 USB to MIDI Interface.
    (3) HP Zbook G2 Mobile Workstation w/t 32GB RAM, Four SSD Hard Drives, Nivida Quadro 4GB Video Card.
    (4) Digital Virtual Organ Software is jOrgan 3.20 / Custom Disposition is my own to mirror the console stops and controls.

  5. #15
    ppp Pianississmo StevenJoelSpeirs's Avatar
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    John, Check out the reply I made to toodles. It has my final game plan for the console. I got your email and returned here to edit the replies accordingly. and included your information about the resistors in my reply to toodles. Thanks, Joel
    Joel
    ----------
    My Organ:
    Rodgers 780 (Asilomar) 1983 #27 of 40 built. Console electronics gutted and replaced with the following;
    (1) Classic Organ Works MIDI Control Unit with optional General MIDI 2 Sound Module (Canada).
    (2) M-Audio MIDIsport 4x4 USB to MIDI Interface.
    (3) HP Zbook G2 Mobile Workstation w/t 32GB RAM, Four SSD Hard Drives, Nivida Quadro 4GB Video Card.
    (4) Digital Virtual Organ Software is jOrgan 3.20 / Custom Disposition is my own to mirror the console stops and controls.

  6. #16
    fff Fortississimo toodles's Avatar
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    Since the Rodgers tabs are momentary, if you run the LED wiring through a reed switch, the tab will only illuminate while pressed--unless you plan to alter the tab rail to remove the momentary action. Do you have a plan for latching the data?

    If you run the LEDs off 12V, and use the 470 Ohm resistors, I get 2.55 mA, and that across 10V that results in just over 1/4 Watt. I chose 10V because similar LEDs have a minimum of 2V drop across them (12-2=10). I don't know the exact spec on the Rodgers LED because I don't know what brand they used or the manufacturer part number. I'd recommend 1/2 watt resistors to be safe.

  7. #17
    ppp Pianississmo StevenJoelSpeirs's Avatar
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    Yes, I thought about that when I was making the parts order from Digi-Key, and talked it through with one of the applications consulting engineers. We came up with a toggling latching switch (push on/push/off) that I can use in series with each LED. This is actually better physically too, as far mounting goes. Just above the magnets of the stop-tabs, is a white PVC plastic area, that is the same build material, as the piston of the switches the engineer at Digi-Key came up with. Having PVC ride on PVC will insure smooth operation, and enhance longevity. Since that area of the back of the stop tab is curved a bit, it will allow for the 1-mm travel of the piston of the switches to have a bit of wiggle-room to comply with their need for +/- 5-mm travel tolerance. I might just end up with something almost as maintenance free as Rodgers original design, even if this is a totally different operational concept. The price for 75 of them was only a few dollars more than the non-latching glass-enclosed reed switches. I agree on the 1/2 watt and made the upgrade on my order since they hand not pulled it yet for shipment. They pull most small lot orders on the 3rd shift, so I caught it in time. Thanks for that math. Tremendous help...
    Joel
    ----------
    My Organ:
    Rodgers 780 (Asilomar) 1983 #27 of 40 built. Console electronics gutted and replaced with the following;
    (1) Classic Organ Works MIDI Control Unit with optional General MIDI 2 Sound Module (Canada).
    (2) M-Audio MIDIsport 4x4 USB to MIDI Interface.
    (3) HP Zbook G2 Mobile Workstation w/t 32GB RAM, Four SSD Hard Drives, Nivida Quadro 4GB Video Card.
    (4) Digital Virtual Organ Software is jOrgan 3.20 / Custom Disposition is my own to mirror the console stops and controls.

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