Schematic reading help MIDI IN DIN

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Bananagab

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Hi,

I'm a beginner at this kind of electronic stuff, I never used a Tennsy only Arduino. What are the two diodes at between the 220 resistor and the pc900? And do I need them for my midi input circuit to work?

Thank you!


midiin.png
 
First, there is only one as the second is inside the PC900. The inside one is a current switch on the internal buffer

Second, that's schematic is specifically for T2.0 and are you really using that?

Third, there should always be three things in a short list!

...but I'm fairly sure it's polarity protection in case the MIDI In current has been reversed somehow. And similarly for the T3.x version above on the MIDI page.
https://www.pjrc.com/teensy/td_libs_MIDI.html
 
First, there is only one as the second is inside the PC900. The inside one is a current switch on the internal buffer

Second, that's schematic is specifically for T2.0 and are you really using that?

Third, there should always be three things in a short list!

...but I'm fairly sure it's polarity protection in case the MIDI In current has been reversed somehow. And similarly for the T3.x version above on the MIDI page.
https://www.pjrc.com/teensy/td_libs_MIDI.html

Yes I will be using a 2.0 since the project I'm currently attempting to do use it. So I don't really need the diode if I'm using the MIDI connector "as intended"?

View attachment 19397
 
You don't need it if you never need it.

Getting that wiring wrong on an out or thru circuit is really easy as it's not immediately clear which direction the wiring diagram is meant to show; face or contact side?

The fact it's standard suggests it happens.... the part is a few cents... add it if you can.
 
The PC900 opto-isolator has been long since discontinued. Use a 6N137 in it's place. The pin out is different, but there are plenty of example circuits for MIDI in. A 6N138 based circuit would be fine too.
 
(CA-033) MIDI 1.0 Electrical Specification Update [2014], available on MIDI.org (free, requires registration for download) has a lot more detail than the original and very sketchy MIDI 1.0 electrical "specification". In particular it adds details for changes to the MIDI out low voltage signalling, explains the current loop operation, and suggests changes for electromagnetic screening. In general it is a lot better written.
 
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