[sdiy] OT: MIDI interface question

[Trevor Page]

Hi Michael,

> This is inverting the MIDI data coming in; is that supposed to be the
way it 
> works?

Essentially this does invert, yes, if you think of it that way. When
there is a current flowing through the MIDI cable to the LED in the
opto, the phototransistor inside the opto causes pin 15 to be pulled to
ground.

> I happen to have a 6N139 on hand for this, is it a suitable device 
> for the task?

Yes. I'm no opto expert but I have used the 6N136 quite often for MIDI
and found it to be a very good part. 

I have found a variation of the design where the output from the
optoisolator is buffered - I prefer this:

http://www.borg.com/~jglatt/hardware/pc_intfc.htm

Cheers

Trev

. .  .   .    .     .      
t at introspectiv.org
http://introspectiv.org/ 


-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Michael Ruberto
Sent: 15 April 2003 05:44
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] OT: MIDI interface question




My Music Quest 2Port/SE MIDI interface finally burned out so I want to 
construct the adapter to get the MIDI from my computer's joystick port.
It 
should do for now. I am looking at the schematic for this adapter and it

shows the optoisolator sinking current from pin 15 on the joystick port.

This is inverting the MIDI data coming in; is that supposed to be the
way it 
works? I happen to have a 6N139 on hand for this, is it a suitable
device 
for the task?

Thanks in advance!!

~M



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