[sdiy] Midi opto isolation

[Grant Richter]

Ha, ha, ha...

This is actually a throwback to before the 8 bit microprocessor world.

Before the RS-232 suggestion, there was the 20 ma current loop.

MIDI is based on that technology.

These were used for teletype terminals, before the advent of the  
"glass teletype" you are using now.

I guess the theory was that it would be harder to induce a noise  
current than a noise voltage. So they must have picked it for  
reliability, the interface parts cost is more expensive than RS-232.

On Jan 1, 2008, at 12:09 PM, Sean Ellis wrote:

> Over the years I have picked up some modules that have trouble with  
> complex midi signals. I'm considering ways to fix them like  
> improving the midi inputs stage but I'm curious, why have the  
> signal isolated? Surely using the isolation lowers the quality of  
> the signal with very little benefit, is it really needed?
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