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Midifiying old Mac RS-422 Midi Hardware


Altitude
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So now that I have some extra 1x1 GM5 modules, I decided to look at adding USB Midi to my JL Cooper CS-10 control surface for cubase. I bought this thing NIB for $25 but it was the old Mac RS-422 Serial interface (hence the price). The way RS-422 and midi worked on the old macs was a simple hardware conversion so it was simply midi over RS-422. The way i got this up and running was simply connecting an old Motu fastlane mac midi interface to the RS-422 port on the CS-10 and midi in and out to one of my GM5s. This worked fine but it was a tangle of cables (RS-422, 2 midi, and the wall wart) but i would like to par everything down to one USB cable.

First thing I needed to look at was the current draw of the control surface. It is powered by a 9V Dc adapter which simply runs into a 7805 vReg. I bypassed the reg and ran it directly off a my bench PSU to see what it pulling and it draws a reasonable 130 mA.

Next step was powering it off my 1x1 GM5, plugged in the fastlane and fired it up. Works like a charm!

So this will work however I will need to scale down the fast lane to a simple one channel job.

The conversion is simply done with a 1 mHz clock, and a 4049 hex inverter.

midischeme.gif

I should not need the opto since everything will be running off the same supply (i'll need to verify this though, any input here would be appreciated) and instead of using a crystal, I'll use a resonator. The motu uses a 2 pin resonator with some load caps and for whatever reason 1 MHz crystals are $13. I have laid out a simple board to connect between the GM5 and CS10 and will be etching next week to see if it works!

Edited by Altitude
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