At 02:24 PM 4/27/98 EDT, you wrote:
>I was hoping someone could provide a simple explanation of an optoisolator
and
>an example of its practical use.
>
>
>Jon
>

Hi Jon,

        An optoisolator is a LED/phototransistor pair typically enclosed in a DI
P8
plastic package. The LED and phototransistor are electrically isolated from
each other but the light from the LED is allowed to pass thru to the
phototransistor. All external light is shielded by the package. The pins of
the LED and phototrans are brought out on the pins of the package. So, when
you turn on the LED, the phototransistor turns on.
        The purpose is to allow information exchange from one circuit to another
without any electrical connection. The purpose of this might be to protect
a sensitive circuit from high voltages (i.e., a circuit which produces and
uses HV needs to communicate with a PIC, for example). It also might be to
prevent coupling of additional signals which might occur over wires going
between the two circuits, but which can be prevented from being transmitted
through the LED.
        So, if you were building a circuit which, say, allowed a PIC to count th
e
RPM of your car's engine via the spark plug voltage, you might  make a
small circuit which turned on the LED whenever the spark plug fired, and
then use the PIC attached to the phototransistor to count the pulses. The
advantage of doing this versus some type of direct connection is that it is
easier and more reliable to make the LED immune to voltage spikes
(especially unexpected ones) than it is to try to allow the PIC to handle
them.

Good luck,

Sean

+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
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