[TRLog] Opto Iso Keying

[punkymcd@pacbell.net]

Sorry forgot to refer the article.

It appeared at the URL www.qsl.net/ae0q/contest/opto_key.htm. Used for a
serial and LPT printer port keying.

n6tr@teleport.com wrote:

> > Can anyone give me a good reason for the diode in series with the LED in
> > this circuit? It looks like a diode in series with another diode (LED)
> > to me.
>
> Not sure of what circuit you speak.  If the current is being set with
> a current limit resistor, then you shouldn't need a second diode in
> series.  However, removing it will change the resistor value to get the
> same current.
>
> Tree




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