Opto-couple confusion – 6N137 or 6N138?

Preamble

Following on from USB to MIDI connections, and Notes on optocouplers, I realised that I, myself, had become a bit confused and mixed up my optocouplers.

Trash80 recommends using a 6N138 in the ArduinoBoy, see the schematic. I had subsequently order a batch of 6N138, in order to build an ArduinoBoy, see Making your own ArduinoBoy. Then I started looking at the use of optocouples for other MIDI applications. However, many other users recommend 6N137 for MIDI applications, and I ended up getting the two confused.

So, how different are they? Are they interchangable? Is the 6N138 the right optocopuler for the ArduinoBoy?

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Minimal AVR kit

Preamble

Many moons ago, before I knew anything about Arduino, I bought a “minimum ATmega kit” from eBay, pretty much like this, DIY ATMEGA8 Minimum System Board ATmega48 ATMEGA88 Minimum System Board AVR Kit. It arrived, I built it, I put in in a box and forgot all about it until today, when I came across it.

But once you’ve made it how can you use it and what are the buttons for?

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