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

[Martin Klang]

Well the input, if MIDI compliant, is protected by an optocoupler. Shouldn't that be enough?

I've seen plenty of DIY and not-so DIY circuits where the output comes straight off an MCU pin, which makes it susceptible to over-voltage and current. I'd put a transistor in line at least.

 
Martin

 
-----Original message-----
From: Mattias Rickardsson <mr at analogue.org>
Sent: Thursday, June 27 2024, 4:29 pm
To: grant musictechnologiesgroup.com <grant at musictechnologiesgroup.com>
Cc: synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: Re: [sdiy] MIDI cable impedance and MIDI In ESD protection?
 <grant at musictechnologiesgroup.com> wrote:
The latest MIDI electrical spec CA33 shows "optional ferrite beads to  improve EMI/EMC performance (FBx 1K @100MHz)"as well as "optional small  capacitor (0.1 μF typical) to improve RF grounding", along with diagrams.
 And I realize that the TRS MIDI spec (RP-054 from 2017-18) writes an unspecific answer to my other question:
 "Because TRS connectors are often used for other (non-MIDI) purposes, manufacturers are strongly advised to add protection circuitry (e.g. to handle the case when a DC-coupled headphone driver is connected to a MIDI output)."
 In the world of massive Eurorack systems and tiny plastic synths I expect that pretty loud signals are sometimes connected to MIDI Ins & Outs when confusing TRS MIDI with audio cables. But I wonder what the MMA would suggest that this protection is made, not only in the output case that they mention as example. :-) 
 /mr

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