MIDI directly to an Arduino

All kinds of Arduino MIDI projects use some kind of an 'isolation' between the Arduino and the MIDI port, like TRIAC or some inverter IC. Is this necessary? Can't the MIDI port be connected to the Arduino directly?

I've never seen a triac being used in MIDI interfaces. You do need an opto-isolator for standard-compliant MIDI inputs. Strictly speaking, MIDI uses a current loop for communication, not voltage levels.

If you don't use the opto-isolator, you risk getting either ground loops, or having two different "ground" potentials, one on the MIDI device, and one on the Arduino. The first one can result in large currents through your ground wires, and introduces noise on any audio equipment connected to it. The latter means that signal levels are meaningless, and if the ground potential difference is large enough, you might blow up one or both of the devices involved.

If the MIDI device and the Arduino can safely share a ground, you can probably do without the opto-isolator.

From the MIDI standard (see midi.org):


[u]Reference schematic here[/u].

Not a TRIAC. The spec "requires" an opto-isolator on every input (not the outputs). I assume you have to have optical isolation if you're selling a product and you want to claim "MIDI compliance".

It should generally "work" without it, but it does function as an inverter so if you don't us it, you'd need to add an inverter or invert in software.

My mistake, I meant opto-isolator. Anyways thanks for the help, ill definitely look into it