[sdiy] MIDI cable impedance and MIDI In ESD protection?

[Roman Sowa]

There is such thing as optocoupler with 2 LEDs back to back, so polarity 
does not matter for them. I used them long time ago in one of my MIDI2CV 
converters. Unfortunately it's not very fast, so it needs a little trick 
to make it work at MIDI speed. I think it was ACPL-214.
Fun fact - connecting MIDI jack in reverse is number 1 reason for user 
claims that the product doesn't work.

Roman

W dniu 2024-06-28 o 00:06, Mattias Rickardsson pisze:
> On Thu, 27 Jun 2024 at 20:55, Andrei Kudryavtsev 
> <andrei.kudryavtsev at gmail.com <mailto:andrei.kudryavtsev at gmail.com>> wrote:
> 
>     Speaking of TRS mess, found this one in the recent application list
>     for MIDI innovations:
>     https://midi.org/innovation-award/psimidi
>     <https://midi.org/innovation-award/psimidi>
> 
> 
> Oops, that has been solved in commercial products for over 5 years.
> But without those extra diode voltage drops!
> 
> (Assuming 1.9 V drop for the optocoupler and 2 x 0.3 V drop for the 
> Schottkys, and the new 3.3 V (+/- 5 % on the lower side) logic level, 
> there's 0.635 V left for the 220 ohm resistor. The current is then only 
> 2.9 mA, far below the required 5 mA. Oops2!)
> 
> (It would need to have 127 ohms instead of 220. But with 5 V (+/- 10 % 
> on the higher side) logic level, and 1.9 + 0.3 + 0.3 V voltage drops, 
> you get 3 V over the resistor. 23.6 mA is above the specified Abs Max 
> input current of the 6N138 optocoupler suggested in the MIDI spec, even 
> if the 6N137 used here will survive. Oops3!)
> 
> I'm sure similar gender-agnostic TRS MIDI In jack solutions must have 
> been implemented by several manufacturers by now? It was a bit weird to 
> see different brands using different polarities when TRS MIDI emerged, 
> and even more strange to see MMA omit a solution for it in the new 
> standard. :-)
> 
> Thanks for the reading tip, Andrei!
> 
> /mr
> 
> PS: I wrote "TS" in my first message, mistake - should have been "TRS". 
> Sorry.
> 
> 
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy at synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace at synth-diy.org