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Scheater5
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PostPosted: Sat Jul 01, 2017 1:47 am   Reply with quoteBack to top

X-Post from the Kiesel forums - I dunno if any Carvin amp people still go there since the split.

So, I've had a Quad X for a while now, and I love the thing. But anybody who has one knows the midi implementation is pretty lackluster - it was just before the days of robust midi integration. You can change the channels with Program Changes, and that's about it. But, it had a footswitch - FS77 - that had more direct access to the reverb, graphic EQ bypass, etc. I was at Best Buy for something completely unrelated, and I noticed a super simple little USB-serial cable - exactly the pins and size of the connection for the FS77, a jack apparently called RS232.
Well, I've got a Raspberry Pi Zero itching for a project, and I figure if I can get the hardware connected, the rest should be doable. Except, my Google-fu has failed, as I cannot find even where to start on such a project. Ideally, I'd like to be able to send MIDI-over-USB from a footswitch (either a Line 6 Helix or a FBV Express - which is surprisingly programmable) sending CCs, not program changes, to the Raspberry Pi, and then out the USB-to-Serial cable into the FS77 connection to switch channels on the Quad X and turn the EQ on and off (the reverb is kinda lackluster).

So:
Helix - [Midi CC] - Usb cable - Raspberry Pi - Usb-to-serial cable - Quad X

I could have sworn I remember someone trying to make an aftermarket pedal for the Quad X at one time, but I can't find it on the forum or with a Google search. If anyone has done something similar and can help me out, or just point me towards some resources, that would be greatly appreciated.

(Side note - I figure adding in USB-midi to this preamp will up it's value, especially since it is non-invasive. I'm considering replacing it with a Kingsley preamp, since I'm already used to only having access to one channel at a time on the Quad X. If anyone is interested in buying the Quad X once my name comes up on the Kingsley back-order, PM me)
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tms13pin
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PostPosted: Sat Jul 01, 2017 6:42 am   Reply with quoteBack to top

If you go into the technical docs area on this site:

http://www.carvinmuseum.com/techdocs.html

You'll see schematics for the Quad-X as well as for the FS77 (scroll down a bit). They should give you all that you need.

--Tom
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Scheater5
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PostPosted: Sat Jul 01, 2017 9:40 am   Reply with quoteBack to top

Indeed, I had found that schematic. I seem to have reached a software problem - I have no idea how to take midi signals in, and have them send the appropriate signals to the Quad X. My schematic reading is pretty basic, but near as I can tell the Quad X just wants to see the various pins grounded out - like a typical TRS channel switching pedal you'd find on a Fender, etc. I've found ways to send midi down the serial cable from some fine work done on arduinos, but nothing about just "receive midi signal, then ground pin"
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tms13pin
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PostPosted: Mon Jul 03, 2017 12:26 am   Reply with quoteBack to top

Is there a parallel output port on your R-pi?

--Tom
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Scheater5
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PostPosted: Wed Jul 05, 2017 2:16 am   Reply with quoteBack to top

So, I did some tinkering with a buddy of mine who is more knowledgeable about electronics than me. It took some digging, and quite a while chasing a red herring ("I mean, that's not how DB9 ports work. It must be sending data of some kind") before we determined that, indeed, my initial reading of the schematic is correct - the Quad X is expecting the various pins to be grounded or not to indicate various functions. The good news is that it's smart about channels - you can't activate 2 channels at once. Whichever pin most recently was grounded is the only active channel.

So, any hope of using the USB-to-serial converter is out. A raspberry pi doesn't have a parallel port, but it does have GPIO pins that you can connect a wire to and then ground it or not with some code - but my buddy said it would be even easier with an Arduino, which I duly ordered up from Ali Express and we are now waiting on it to arrive. But this should totally be do-able, and I'm pretty excited about it. We've already sketched out some code, and we should be able to select any given channel, turn the EQ, Reverb and Master FX loops on and off, and even choose two channels to toggle between on a single footswitch - all with MIDI commands sent from my current footswitch (Line 6 Helix), and passed to the Arduino and then sent to the FS77 connection, which is pretty exciting to me - it brings the Quad X up to modern midi capabilities.

There was some disbelief on his part that Carvin would make the port function in that way. It was, in his words, "super janky." I suppose that's why that sort of connector never caught on - that and being supplanted by decent midi implementation.
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tms13pin
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PostPosted: Wed Jul 05, 2017 7:12 am   Reply with quoteBack to top

Yes, the Arduino has a parallel port and that'd be the easiest way to do this, just assign a pin to each switch function and output the correct 0 or 1 to switch it on or off.

--Tom
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