[sdiy] GEM / GeneralMusic SX-3 service manual

[Tom Wiltshire]

Yeah, have to say, some MIDI variant with a proprietary plug/pin-out would be my first guess too. It’s not that hard (ok, dead easy) to change the baud rate/pin out and call it something else. Even if actually it isn’t.

==================
       Electric Druid
Synth & Stompbox DIY
==================

> On 15 Jul 2018, at 21:11, rsdio at audiobanshee.com wrote:
> 
> Timing is most likely asynchronous serial, since there’s no obvious clock line. It could very well be MIDI. It doesn’t seem to be too old for that. The GEM S2 started in 1992 (?), so the SX-3 should not be any earlier than that.
> 
> I’d recommend wiring up a MIDI setup to that pedal input, send it various MIDI notes, and see what happens. Before you wire it up, measure the impedance to ground (and power) of the Rx channel, just to make sure it won’t damage your MIDI output if it’s shorted to something (i.e. if it’s not actually a MIDI input).
> 
> What’s the exact DIN plug? How many pins? What’s their angle? (there are some variants of DIN that have the same number of pins, but they’re spaced differently).
> 
> Brian
> 
> 
> On Jul 15, 2018, at 12:02 PM, Rutger Vlek <rutgervlek at gmail.com> wrote:
>> Hi Brian,
>> 
>> I know, beautiful thing, a switch matrix. This works differently though. I've been able to identify the pinout of the plug and it carries two types of grounds, one for shield and one for power. It carries a +5v supply line and provides an Rx data input pin. So the original pedal for which this input was designed must carry some active electronics. I haven't yet nailed how they would gave done timing of the Rx channel. Anyone fancy a guess at what would have been in there? 
>> 
>> Rutger 
>> 
>> Op zo 15 jul. 2018 20:34 schreef <rsdio at audiobanshee.com>:
>>> You only need 11 or 12 pins for a matrix to support a 30-note pedal board. How many lines on the DIN plug?
>>> 
>>> Brian
>>> 
>>> On Jul 14, 2018, at 1:25 AM, Rutger Vlek <rutgervlek at gmail.com> wrote:
>>>> Additionally, another question for GEM conaisseurs: there's a pedalboard input (looks like a DIN-variant plug) that seems intended to be used with bass pedals. Anyone know which type of pedals could connect to this? Or what the control protocol is? I'm suspecting it's either a straight diode-matrix-scan input (but don't think there's enough lines to make up the required notes), or communication line to some kind of multiplexer or shift-register internal to the pedals. I have pedals from another brand here, with straight switch-outputs and I'd love to modify it to work with the Gem.
>>> 
> 
> 
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