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

[eidorian at aladan.net]

Thanks Neil, this is an interesting (if somewhat disappointing) read.  
It's a shame they haven't come out with a more forceful position on this 
given how long they're had to do so.

That said, it's pretty clear that to add any sort of genuinely _useful_ 
power specification to the MIDI standard risks introducing 
incompatibilities that are just not safely backwards compatible with 
existing equipment.  I think the best approach would be a new physical 
interface, with simple (i.e. unpowered, ideally) but well-defined 
converters to allow for integration between old and new.  I won't hold 
my breath though :)

And yeah, I personally won't be powering anything from MIDI in the near 
future, and I have no plans to use any MIDI Solutions gear!

Cheers,
A.


On 2015-09-10 18:30, Neil Johnson wrote:
> 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