Web Synth with Particle Photon Part 1: Hardware

Recently someone asked me to look at the Particle cloud platform as the basis for a project. So, I did what any reasonable person would do and used it to hook the Internet up to my .com modular synth 🙂

The Build

I bought a Photon from Amazon and hit up the local electronics surplus place for a small breadboard and a 5-pin, 180 degree DIN jack.

The construction is super simple. Following the MIDI Electrical Specification Update*, it’s just a couple of resistors and a receptacle:

MIDI output schematic

Since the Photon is a 3.3V device, I followed the 3.3V chart and used the Photon’s 3.3V core voltage to keep things simple:

Easy, right? Well…

You only had two options…

If you look carefully, you may notice something fishy about the way the MIDI receptacle is wired… Based on the MIDI wiring diagram, pins 4 and 5 are swapped! When I first built the circuit and nothing happened, I suspected that the MIDI wasn’t getting out of the Photon.. or maybe at the wrong baud rate.. or maybe some bad commands. After looking at it with a scope those things seemed to be ok. I just flipped pins 4 & 5 and BAM. Works.

This was baffling since it seems to be directly opposite the MIDI standard, but for some reason the standard doesn’t say whether it is illustrating connectors from the front, back, plug, or receptacle. It’s lightly implied that it shows the pinout from the cable point of view…

Fortunately Practical Usage Blog came through with this illustration to back up the working prototype’s pinout:


It also agrees with continuity measurements from the Sparkfun MIDI shield, although their schematic symbol is disappointingly just as confusing…

It’s nice to have confirmation from other sources, but the best confirmation is that it works this way. Hard to argue with that.

On to the firmware!

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