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  Thursday, 29 March 2018
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I'm new to electronics, so forgive not using official terms.

I want to make a MIDI project with an Arduino (Mega) and want to have 3 MIDI input channels. Currently on my breadboard I use 6N137 optocouplers which seem to work.

However, I also see schematics using a 6N138 or 6N139 optocouplers... Since I'm not so good at reading datasheets, let alone comparing them (since they use somewhat different terminology).

Since I need to use 3, maybe I thought I can use a so called multiple-optocoupler like this 4 channel optocouper

Also I found LTV847

However, is it comparable to a 6N137? And would I still need to use a diode and resistors as in the schematic:http://www.apogeeweb.net/article/25.html

https://www.pjrc.com/tech/midi-drums/sch-midi.gif

Or should I use a 6N138 or 6N139 or another since the 6N137 has disadvantages?

Or are there even better/more suitable multiple channel optocouplers than the one I found?

(the reason is want to check if I can save some space by using a multi channel optocoupler instead of 3 separate ones, including resistors/diodes etc).
4 years ago
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I have a circuit here from 1987 project where the part between the optocouple and the connector is just the same as the one you show.

I would expect that you could use a multi optocouple, as long as the individual oc devices are TOTALLY electronically and optically independant. Can you guarantee that? The oc is there for protection. To protect your device from unwanted input voltages/current. No other reason.

The diode and resistor seem to be a standard part of the circuit. I would assume they should be there unless you know better (i.e. regarding the exact requirements of the oc device)?

Your use of the words 'midi channel' may be incorrect. A midi channel is something specific within midi data. I assume you just require 3 midi inputs (sockets) and each one may be carrying data for the usual 16 midi channels?

Geoff
Every MIDI port has 16 channels so one 5 PIN DIN MIDI input has 16 MIDI channels.

Do you need 3 MIDI channels or three MIDI inputs (16 channels X 3 MIDI Ports= 48 Channels)?

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