[sdiy] ODP: Re: MIDI notes filter which is also a MIDI converter for Junos ?

Roman Sowa modular at go2.pl
Sun Dec 29 16:25:56 CET 2013

> I don't agree here. The specification calls for a 5mA current loop, and you can do that at 3.3V as well as at 5V. In fact, I have. Simply adjust the 220R resistors in the MIDI OUT and you're done. As long as the voltage you provide is enough to drive the opto at the far end (e.g. >1.2V, or say 1.5V for safety), the exact level shouldn't be an issue. Isn't that partly the point of using a current loop? MIDI is agnostic about the voltage level - it could be 12V, 5V, or nowadays 3.3V, as long as it's 5mA loop, it's legal.
> In fact, I'm a bit surprised you haven't done the same yourself at some point, Roman. Haven't you got some little 3.3V uP-based MIDI gizmo knocking around somewhere?
> 2 cents,
> Tom

Well, I did, and I'm a bit ashamed of it now. It was little midi keyboard encoder powered from two AAA cells. Output resistors were 150 ohm to compensate for lower voltage. I discontinued it about 8-9 years ago, although I can't recall anybody complaining about any problems.

In every manual I clearly state that the midi controller will work even when powered below 3V but its operation is not guaranteed then. User's choice.
I use 5V in any MIDI OUT jack now.


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