[sdiy] MIDI phantom power...over 5 pin MIDI connector ?

[Neil Johnson]

Found the discussion I had with the MMA on this issue:

http://www.midi.org/cgi-bin/forum/forum.pl/forum.pl?m-1171180161/s-all/

Neil

On 10 September 2015 at 09:58, Neil Johnson <neil.johnson71 at gmail.com> wrote:
> What I find particularly funny/frustrsating/disappointing is how many
> people don't understand the MIDI spec.
> All this talk of "5V" and "220R resistors" completely misses the point.
>
> *sigh*
>
> Here's a clue: the text of the standard makes no mention of voltage.
> Chapter 2, page 1, "HARDWARE".  The circuit given on page 2 is an
> illustration of one implementation.  I've also discussed the wording
> in the standard with the MMA and their response to the vagueness in
> the standard is "well no-one's pointed this out before, and we don't
> quite understand why the spec was written in this way, so, umm, la la
> la la..."
>
>
> Neil
>
>
> On 10 September 2015 at 09:29, Ove Ridé <nitro2k01 at gmail.com> wrote:
>> On 10 September 2015 at 09:40,  <eidorian at aladan.net> wrote:
>>> I just re-read the original post, and it might be that JP isn't asking how
>>> he can get power from a MIDI cable, he might actually be asking a subtly
>>> different question: how can he *send* more power over the two MIDI pins
>>> (presumably without affecting the ability of those pins to transmit MIDI
>>> to
>>> older devices at the same time).
>>
>> The MIDI-DIN states that pin 2 should be connected, if nothing else, through
>> the shield. Are there really cables around that have pin 2 completely
>> unconnected?
>>
>>> But yeah, there's no fun to be had doing this.  Any device that requires
>>> your "high powered" MIDI-out ports for power is going to damage your
>>> "normal" gear if you ever plug it in accidentally :-(
>>
>> I don't see how. A compliant, regular output device should have 220 ohm
>> resistors in series on both pin 4 and 5 to limit the current and should
>> handle even being indefinitely shorted. Likewise, a regular input device
>> will have 220 ohm in series with the optocoupler. 5/220=23 mA and that's
>> being really pessimistic and ignoring the LED forward voltage drop.
>>
>> --
>> /Ove
>>
>> Blog: <http://blog.gg8.se/>
>>
>> "Here is Evergreen City. Evergreen is the color of green forever."
>>
>>
>> --
>> /Ove
>>
>> Blog: <http://blog.gg8.se/>
>>
>> "Here is Evergreen City. Evergreen is the color of green forever."
>>
>>
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>
>
>
> --
> --
> http://www.njohnson.co.uk



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