[sdiy] Updated MIDI Spec for 3.3v

MTG grant at musictechnologiesgroup.com
Fri Aug 11 17:33:44 CEST 2017

I found out from the guy at MIDI Solutions since he's making some tweaks 
to his products.  There are also a few blog entries on the MIDI.org site 
about a new standard smaller connector, and a few comments about what 
people "out there" have been doing with 3.5mm stereo jacks.  Not sure 
that's the way they'll go but it would be nice if they picked a 
connector that's easily panel-ized, inexpensive, available and isn't 
already used for something else in our repertoire.

That doc I sent a link to was from a 3rd party site (and a .DOC as 
well).  I didn't bother looking on MIDI.org for PDF.


On 8/11/2017 7:52 AM, Neil Johnson wrote:
> I remember discussing this very topic on the midi forum years ago....and 
> it took them until last year to finally publish something.
> If I remember rightly it was on a thread about drawing power from MIDI.
> Neil
> On 11 Aug 2017 15:26, "MTG" <grant at musictechnologiesgroup.com 
> <mailto:grant at musictechnologiesgroup.com>> wrote:
>     Maybe I'm the last to know, but there appears to be an official word
>     on this:
>     https://mitxela.com/other/ca33.pdf <https://mitxela.com/other/ca33.pdf>
>     I know people have been doing their own thing regarding the series
>     resistors for the current loop.  I also noticed this caveat here:
>     https://www.midi.org/forum/492-certain-midi-equipment-for-3-3v
>     <https://www.midi.org/forum/492-certain-midi-equipment-for-3-3v>:
>     "The MIDI specification specifies a 5 mA current loop, and shows
>     three 220 Ω resistors to limit the current when used with a 5 V
>     transmitter.
>     When you have a 3.3 V transmitter, the two resistors in the
>     transmitter must be smaller to get the same current, as shown in the
>     Electrical Specification Update.
>     The receiver does not need to know what voltage the transmitter
>     uses; it always uses the same 220 Ω resistor. All transmitters are
>     designed to work with that same receiver circuit. This means that
>     all transmitters and receivers are compatible.
>     (The receiver can use either 5 V or 3.3 V as supply for the
>     optoisolator; this part of the circuit is isolated from the current
>     loop, and does not affect compatibility of the MIDI interface. But
>     note that only the PC900/H11L1 optoisolators can run at 3.3 V; other
>     common models like the 6N137 or 6N138 require 5 V.)"

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