[sdiy] MIDI Optocoupler

[Bob Weigel]

Most of the specs are of little consequence...particularly speed (since 
hey we're only at ~32Kbit/sec right?).    Current of course well..the 
output has to be able to handle 5V through itself and a 220ohm resistor 
to what ever it's driving.  So...that's of little consequence either.  
The real considerations are just that the thing has enough efficiency to 
run off that amount of current delivered by the lowest output chip used 
to buffer the MIDI out signal.   AND that it's the right type of device 
(phototransistor outputs recommended usually as I recall..)  -Bob

Tim Parkhurst wrote:

> Hi All,
>  
> Just came across a whole bunch (like 2000) of a Philips 4N35 
> optocoupler. I've seen these listed in some Sound Blaster to MIDI 
> schematics, so it looks like they're okay for use in MIDI 
> applications. What I'd like to know is, what is really the determining 
> characteristic for a MIDI optocoupler? Speed? The 4N35 has a switching 
> speed of about 3uS, so (1/.000003)/2 = a maximum switching speed of 
> approx. 167kHz right? (divide by 2 because each cycle is two 
> transitions, and 1/3uS to get frequency... right?) Anyway, if this is 
> correct, then this part should be more than fast enough for MIDI. What 
> about current capability? Any other factors to look at when picking an 
> optocoupler?
>  
> By the way, if these things are good for MIDI, I'll sell 'em real 
> cheap since I have so darn many (something like $2 + shipping for a 
> tube of twenty, I have to see how many are in a tube).
> Tim (right?) Servo
> -- 
> "Imagination is more important than knowledge." - Albert Einstein