AVR-Chat

>
>Yes, I'm currently using a transistor but didn't know if a more preferred
>practice was to use an opto.  I'll continue with the transistor.

This is the fun part, where you get out of the software side, and have to 
deal with a little hardware. Everything has it's weaknesses.

The transistor, for example, should have a resistor between the port pin 
and the base, to limit current when the port pin is high, to some 
reasonable value, determined by the load current requirement and the 
transistor beta.

It also needs a resistor to ground, so that you can be sure that it is OFF 
when the pin is tristated during reset.

You can use a 2N7000 Mosfet, which eliminates the base current requirements 
and calculations, but that also needs a turn-off resistor. In this case, 
just large enough to keep the maximum guaranteed leakage current from the 
AVR pin from getting up to the mosfet's threshold voltage.

If these are driving inductive loads, you can protect them by adding an 
appropriately sized zener from collector/drain to ground, but beware, this 
is dumping the flyback current into your processor ground.  You can and 
should also put a conventional diode across the inductive load.  Both may 
not be needed, but I'd want some measurements before removing either 
one.  "I tried it and it worked" doesn't count as a measurement. :)

Too many hobbyists miss that last bit, and publish designs that "work" in a 
controlled environment, with parts of the right date code, etc.