Watt's the wattage when used on a PIC?

[ERMEGM]

I'm just wondering what a voltage divider plus a zener would cost opposed to a voltage regulator to limit the input.


Yes, most zeners must have current limiting resistor. I say most cause as soon as I say all then someone will post one that doesn't.


This sound like you're trying to make a logic gate for the PIC. There 's a good example in the PBP manual of how to do this.


You could use a transistor with the collector using your 5V supply and voltage divide the input to the base of the transistor. You'd still need a pull down resistor so you're not saving much. You'd end up with a higher parts count but not necessarily lower cost or reliability. Optos in essence are transistors and you've said your not having much luck with them. Though a 2n2222a and a couple of resistors aren't very expensive. If you wanted to go this route it's probably cheaper and easier to do the voltage regulator at the input.


I'm sorry to say math is math and it's been done here already.

Disclaimer: I've not seen your schematic and I'm often not good with word pictures. If I've botched something I apologize.

Here is what I am speaking of. The left schematic is the one we are all talking about. The right schematic is one that I have seen a couple of times now. Still a high value on the top and smaller one on the bottom. What would be the formula for this bad boy?