TRS Midi Connection

Would it be possible to redefine one of the inputs into a midi in using software?

Alternatively what would be involved in adding a 3.5mm TRS midi connection?


1 Like

That’s interesting. I think all you’d have to do add a jack to the right pins along with a vactrol, though Notes & Volts includes a couple of transistors, as well:

All the pins are exposed to you as the designer, so adding a MIDI interface in any configuration is up to you. Design it to use straightened coat hangers or semaphore if you want!

Yeah on the XFM2 platform it’s very easy, and probably because there is some additional logic added to the FPGA module.


But the midi in is actually really close to that using the 4N36 octo.

It’s not exactly a vactrol, since it doesn’t use a LDR. And those transistors are inside the 6N138. Another popular choice is 6N137.

1 Like

@mark.linton I think it is theoretically possible to reuse the audio jacks for MIDI, but it’s impractical. It’s not something that will be implemented in the short term. The issue with reusing the audio jacks for MIDI TRS IO is obviously that you sacrifice that audio connection.

The other issue is that there is no optocoupler on the base board. It’s not clear to me if MIDI TRS adapters actually include an optocoupler internally or not. The Novation Circuit for example has official TRS MIDI adapters that they ship. It would be interesting to know exactly how they handle the optocoupling issue.

In the short term, it’s much easier to rig up TRS MIDI through the expansion pins that would normally connect to a DIN breakout. Or any of the other available pins that can be driven with a UART. This is the practical solution.

I realize that MIDI, both DIN and TRS, are critical for users so I’ll work on preparing official solutions for both.


The somewhat standard TRS-MIDI adapters don’t have an optocoupler.

Just to expand on what @nsm wrote: MIDI on the audio ports would be very very impractical. Just say no.

See this hardware schematic for jack/TRS midi in on the DAISY Pod, who connects to the STM32 MCU.
(note: jumpers R78+R83 and R79+R84 select midi TRS type A or B - only one pair is mounted)

a midi input without an optocoupler is pretty bad… the whole point of the optocoupler is to electrically isolate the source from the destination. a trs connection without opto might induce noise from the midi device connected for example. so if you do an expansion board, the trs connectors could be wired in parallel with the midi din and use the same opto. (but you could only use one at a time)

generally though midi trs seems to be a flimsy connection, din midi is a much better connector/choice…

Hi…I was seeking request the link for interfacing POD to MIDI gadget. I was taking a gander at different on Amazon, and apparently there’s certain distinctions in wiring of the links. Would anyone be able to share the Amazon connect to a link that is known to work with Daisy POD?

The correct MIDI adapter for a POD is a TRS-DIN Type A.

This will work:

BUT, at $15, it’s overpriced.

This is what I use, and it’s a fair price.

So based on the Daisy POD schematic have they implemented a midi connection without the use of an optocoupler? It looks that way no?

No, the POD schematic shows an optocoupler. But , apparently, they didn’t have a symbol for it, so you might misread it.

Looking at the Pod itself, the device is obvious. White chip, 6 legs on bottom of board. (ON Semiconductor H11 series)

So, am I right to understand that in order to take advantage of the MIDI pins on the back of the module I need to create a circuit that involves an optocoupler?

Damn. I was kinda hoping I would be able to just plug the MIDI output pins from my controlling device using a simple DuPont cable.

Optocouplers are super cheap and the circuit is easy. But yes, if you’re not using MIDI over USB, you do.

1 Like

I am using MIDI over USB but it seems extremely unreliable. I have a controller sending CC messages to a few parameters and it works for a while, but then it gets jumpy.

Some parameters are not being controlled at all while using the editor. It is very disappointing really. I am kind of hoping the TRS/MIDI will be more reliable, but then I wonder if the issue is in the software and whether it will even make a difference.