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Simplest way to get Gameport -> MIDI out

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First post, by Vresiberba

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Looking for the simplest way to connect a Sound Blaster to a Raspberry pi with a MT-32 hat . What I understand is there are basically two ways, 1) use a buffer and two resistors and 2) just use resistors and skip the buffer entirely. So just to confirm everything is okay, this schematic is correct, yes?

Also, does anyone know which side +5 is on the MIDI IN on the pi hat, A or B? The DB15 is idiot-proof as it's symmetrical, but the DIN 5 in the schematic can either be seen from the soldering side or looking into the male connector side, for which it would be mirrored. Should be the same on all MIDI IN devices. Googling this was surprisingly inconclusive. I don't want to fry anything.

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Reply 1 of 3, by Jo22

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"I don't want to fry anything."

Your worries are wise. Use an opto-coupler/opto-insulator on the reception side (Pi+MT-32 hat).

I know, it really can be annoying finding a coupler/schematic that's fast enough.
However, it's worth it. Broken hardware is much worse.
Also, the coupler will filter out noise, sheet waves and potential issues.
Stuff that can be annoying or causing other weird behavior.

I'm speaking from experience here. I've built a few MIDI boards for a MT-32 Pi project..
Using a cheap opto-insulator in diode-mode only fixes some speed issues sometimes, also.

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 2 of 3, by Vresiberba

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Jo22 wrote on 2022-11-10, 22:34:

Your worries are wise. Use an opto-coupler/opto-insulator on the reception side (Pi+MT-32 hat).

There already is one on the pi hat and as I understand it, you don't put those on the outputs, only inputs. I also checked the schematic of my JV-1080 and it too has an opto-coupler on the MIDI IN as I plan to use that one as well.

The only thing I need to know is if the schematic is okay and the polarity of the MIDI IN. I'm leaning towards +5 being B and that the connector in the schematic is looking into the connecting pins on the male side. Schematic like these should really have this written into it, it would be so much easier to understand.

Reply 3 of 3, by coldturkey

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As this post shows up on Google searches for midi schematics, I figured I'd respond (even though it's years later and not useful to the OP).

I used to use two resistors on my soundcard midi pins without any other electronics and it seemed to work. But there's no guarantee that every soundcard will work with this method. A buffer like the NAND used in this circuit increases the probability of compatibility (and decreases the risk of damage to the soundcard).

I recently built this exact circuit and can confirm that it works. I even scoped the voltage levels on the output of the NAND gate when my computer was connected to a midi device, and they looked appropriate to deliver the expected current defined in the midi spec.

For the DIN plug, I used a female DIN and matched the numbers in the diagram to the numbers printed on the soldering side (which again, worked).

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