>
> Perhaps it's just me,but this doesn't seem like it would need an
> optocoupler. If you want to use a relay, just put a 1N914 or 1N4148 diode
> across the coil to prevent voltage spikes and it should be fine. Just be
> sure that your relay coil doesn't need more current than the pic pin can
> source.

The problem is that almost always the coil requires more current than a
PIC can source. Reed relays like that Radio Shack 275-0232 part only
requires 20ma though. It would handle the job.

I usually use the optocoupler not only for isolation but to bump up the
current.

>
> I'd be tempted to solve the whole problem with a power darlington (like one
> of the TIP series). Just put the strike between 5V and the darlington's
> collector. Base to the PIC via a 4.7k resistor, emitter to ground. Add an
> additional 1.5k resistor from base to ground,to prevent self turn-on.

Now this sounds like a good idea.

>
> In either case, put a 1N4004 or similar diode across the strike (with
> cathode toward positive - reverse biased) to prevent voltage spikes. A
> capacitor such as a 0.1 uF ceramic disc would also be good across the
> strike. I take it that the strike contains a motor?

Probably an electromagnet.

BAJ