Is this PNP transistor in my MIDI IN correct?

[Deva_Rishi]

@Grumpy_Mike

Remember this standard was made for musicians to work with, not electronic engineers.

I thought i was saying that, but your explanation is probably more clear. Moreover, it was designed by people that had to put warrantee on the equipment they'd sell.

[Grumpy_Mike]

@Deva_Rishi

Moreover, it was designed by people that had to put warrantee on the equipment they'd sell.

A very good point.

[Smajdalf]

@Paul_B

What about ESD?

This is all circuitry inside the device, nothing external. External is on the other side of the opto-isolator.

I am not following this thread closely because a lot of nonsense was posted here (what a shame with such simple circuit). As I understand the schematic it shows output of one device connected to the input of some other device - connected at points marked by (blue) 4 and 5:

@vrll

I took the midi out with the buffer and hooked it up the midi in (and removed the beads, etc)
Now I do have this:

So left hand part of the schematic is output, right hand part is input and the diode is in the right place to protect LED in H11L1 from ESD.

[Paul_B]

@Grumpy_Mike

It's use is to protect the opto isolator in the event of an incorrectly wired MIDI cable or socket.

OK, I have clearly misinterpreted the meaning of the circuit.

@Smajdalf

As I understand the schematic it shows output of one device connected to the input of some other device - connected at points marked by (blue) 4 and 5:

So it appears now.

This is not really an circuit on its own, but nothing more than a concept diagram to analyse the voltages involved.

So ...

@Deva_Rishi

But seriously, that thing should be able to take it.

In an actual MIDI interface, the diode is present to protect against (mis-)connection to a Midi interface which operates at more than 5 V, the rated voltage of the opto-isolator.

@Smajdalf

and the diode is in the right place to protect LED in H11L1 from ESD.

No, just reverse application of a voltage in excess of 6 V.

I shall just quietly go away now ...

[Grumpy_Mike]

@Paul_B

So it appears now.

This is not really an circuit on its own, but nothing more than a concept diagram to analyse the voltages involved.

No it is a full circuit, but the bits that are numbered 4 & 5 represent the plug and socket joining the transmitter to the receiver. To the right of these numbers is the MIDI receiver and the the left is the MIDI transmitter.

So those dots by the numbers signify a cable, which could be miss wired.

[Deva_Rishi]

@Paul_B

a Midi interface which operates at more than 5 V, the rated voltage of the opto-isolator.

Those haven't appeared in my studio so far, but with USB-C the future may hold surprises. But that does make sense though. So to prevent damage from an incompatible device that is connected in reverse. Those guys though of everything.