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Topic: Multiple MIDI-Outs with same data (Read 2482 times) previous topic - next topic

Signal

Hi all,
I try to build a midi-timer based on an Arduino UNO. There is no midi-music-data. Just the Start/Stop/Continue and Clock.

I want to have 8 MIDI-OUTs all with the same data.
Can i just solder them together? And handle them like 1 cable? Or does that suck to much power?

The actual Midi-Ports will sit behind an OptoCoupler 6N138. Does the UNO have enough power from the 5V to drive all 8 outs?

Thank you very much!

RuggedCircuits

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Can i just solder them together? And handle them like 1 cable? Or does that suck to much power?


You'll have to be more specific. What do you mean by "solder them together"? I don't think you'll have trouble powering the optoisolator LED's from the 5V, the question is where do you plan for that current to go? If you expect to use a single I/O pin to power (or sink current from) all 8 optoisolators then that's too much.

You can either use 1 I/O pin for 2-3 optoisolators, or use a high-current buffer or MOSFET to drive all the optoisolator LED's from a single pin.

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Grumpy_Mike

MIDI output doesn't use opto isolators, so all you need is a transistor to drive it, like in this:-
http://www.thebox.myzen.co.uk/Hardware/MIDI_Shield.html

As you are just diving the base of a transistor you can wire all the bases (through a resistor) to the same pin. However you do need the transistor for each output.

Signal

@RuggedCircuits: The basic idea is to use just one TX pin for all the 8 midi-outs (because the same data is sent on every line).

@Grumpy_Mike: Why exaclty do i need a transistor? I am an absolute noob. So i am sure what exactly that thing does there. Whats the purpose of it in that situation.

Thank you guys for your help and time!

RuggedCircuits

Here is a suggested circuit:



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Signal

Oh wow! Now i see how all this is connected... the signal amplification and so on.
I will order the mosfet right now.

Thank you very very much!

Grumpy_Mike

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Why exaclty do i need a transistor?

To provide enough current drive for the receiving MIDI circuits. The designs that don't use one will not always work with all devices.

I wouldn't connect pin 2 of the MIDI socket to ground. That is a common mistake and against the MIDI spec.

RuggedCircuits

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I wouldn't connect pin 2 of the MIDI socket to ground. That is a common mistake and against the MIDI spec.


The suggested MIDI specification diagram has pin 2 connected to ground on MIDI OUT but not MIDI IN.

http://www.midi.org/techspecs/electrispec.php

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Witzman

I would like to do the same,  but the picture from RuggetCircuits is not here anymore.
Can someone explain me in basic english or provide a short picturr,  how to connect the transistors/mosfets and tell me,  which i need?

Grumpy_Mike

What picture is not there any more?
What was the link?

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