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

[Neil Johnson]

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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