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

[Florian Anwander]

Kay from LPZW did this already in 2017 in the Schleußig 
(https://leipzigwest.org/?page_id=173) ... ;-)

Am 28.06.24 um 11:50 schrieb René Schmitz:
>
>
> If you have the space and budget, use two optocouplers: one for each 
> direction, that allows you even to sense which direction it is.
>
> (So you can change the output too...)
>
>
> Where do I collect my prize? :)
>
>
> Best,
>
>  René
>
>
> Am 28.06.2024 um 00:06 schrieb Mattias Rickardsson:
>> On Thu, 27 Jun 2024 at 20:55, Andrei Kudryavtsev 
>> <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
>>
>>
>> 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.
>>
>>
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> -- 
> --
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>
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