5 Pin MIDI Input Circuit Methods

I’ve made a couple of MIDI interfaces in the past on arduino pro micros and nanos and had great success with adding traditional 5 pin midi jacks. In the past, for wiring up a jack, I did something like in this tutorial: Arduino MIDI Note Player. It’s a nice easy and cheap way to add MIDI when you only need some wire and resistors.

But then I came across other tutorials where they put optocouplers into the circuit like in this article: Midi To Arduino. This seems to be more like a genuine MIDI experience since MIDI supposedly uses flashing LEDS to communicate.

My assumption here is that using the optocoupler effectively turns the communication line from electrical to an optical connection.

My questions:
Is the optocoupler method better/safer/more compatible with standard controllers and MIDI devices?

Am I risking anything if I just use a 3v3 serial connection on the 5 pin MIDI connections?

Haven’t posted before but I’m hoping to understand this a little better. Thanks in advance for any answers.

Optocoupler is used in MIDI IN. MIDI OUT typically has no optocoupler. The optocoupler in the receiving side electrically isolates the two devices.

1 Like

Yes, the optocoupler is ‘better’ - it will work in some cases when an actual direct electrical connection aka ‘galvanic’ will fail. Mainly when you try to connect two midi devices that have differences in their AC Power connections - particularly when they’re on different AC circuits, aka different breakers.

Are you risking anything using 3v3 - I think you’re just risking that it won’t work. I don’t think it will hurt-‘fry’ anything anything. Of course, those are ‘famous last words’!

1 Like

Again, it’s important to understand that the optocoupler is only used on the MIDI IN. It’s only a few parts, and it increases the chances your device will work with anything you plug in.

Thanks for the replies. That makes a lot more sense! I purchased some optocouplers for the input side of my future daisy projects.