MIDI Interface Manual

Welcome to the construction manual for the MIDI IN + 4× MIDI THRU Interface, a compact little box whose entire purpose in life is to take one stream of MIDI data and multiply it like a well‑behaved, electrically isolated rabbit. This device is designed for builders who appreciate clean signal paths, modular wiring, and the deep personal satisfaction of knowing exactly where every resistor on the board lives — and why it’s there.

This project combines several classic ingredients of electronic music hardware:

• A 6N138 optocoupler, whose job is to stare suspiciously at incoming MIDI data and only pass along the important bits.
• A 74HC14 Schmitt inverter, which takes the optocoupler’s nervous whisper and turns it into a crisp, confident digital signal.
• A 78L05 voltage regulator, which bravely converts your wildly unpredictable 9–15 V DC input into a calm, dependable 5 V supply.
• And finally, a MatrixPortal tap point, because what’s the point of building a MIDI interface if you can’t also make it drive a lyric display, a robot drummer, or whatever other contraption you’ve decided to unleash upon the world.

All MIDI jacks, switches, and LEDs are panel‑mounted, because you deserve a device that doesn’t rip its connectors off the board the first time someone bumps a cable. Everything connects to the main board through pin headers, giving you modularity, serviceability, and the ability to unplug things dramatically when troubleshooting.

The circuit is built on a 2" × 3" perfboard, which is just large enough to be comfortable and just small enough to make you feel clever. The layout is intentionally simple, the wiring is intentionally logical, and the end result is intentionally robust — a reliable MIDI splitter that won’t add latency, won’t distort your signal, and won’t judge you for still owning that one synth with the sticky keys.

Whether you’re integrating this into a larger system, mounting it inside a custom enclosure, or simply building it because you enjoy the smell of flux in the morning, this manual will guide you through every step with clarity, precision, and the occasional moment of levity. After all, if you can’t have fun while soldering tiny metal legs onto a tiny green board, what are we even doing here.

Let’s begin.

始めましょう