I feel that this is an over-simplification. HP and others have optos that
have bandwidths as high as 10 Mbits/sec. Perhaps in your application this
is SLOOOOOOW. It's true that if you pick up an opto that is constructed
with an led and  photo-transistor (or worse, a photodarlington), it will be
sloooow. As soon as you substitute an opto that is constructed with a PIN
diode and transistor instead of a phototransistor, the bandwidth goes up to
about 1Mbit/sec. So you pick your performance and pay the price....

Regards, Jim Ham

At 08:23 PM 1/16/98 -0500, you wrote:
>This is for anyone contemplating using opto couplers or similar devices in
>projects.
>
>    "USE ONLY AS A LAST RESORT!"
>
>Why?  They are SLOOOOOOOOOOW!
>
>So before you design them into a project, go to SIEMENS web site
><http://www.siemens.com>, find the opto app notes section and get app notes
>1, 2, 4 and 5 as a minimum. They are in .PDF format and although small,
>ther is enough info there to put you on the right track.
>
>Good luck with your projects,
>Bill
>
>
Jim Ham, Porcine Associates
(415)326-2669 fax(415)326-1071
"http://www.porcine.com"