----- Original Message ----- From: Subject: Re: [EE] Pull-up/down resistors > value or a low one (100k / 1k) and the level > of electrical noise expected to be received by the pin. To some extent, this is the artsy part. If I have an input pin, and maybe it's driving several other gates, I may need a little lower value to drive all those gates. But if it is only an input, say pulled to ground by a pushbutton now and then, all I *really* have to do is drive the PIC input pin. Different pins have slightly different specs, but they all require very little current. From that perspective, why not put a very high value there. I could probably use a couple of megs, or at least hundreds of K, and still get enough current to raise the pin. The problem is that the PIC input presents a very high impedance, and if the rest of the line is also high impedance, then it will be easy for any nearby lines to get that line to dance with it. We generally don't like that, so we go with a little more current. Most of the time, 4.7K works just fine, or 47K. But if the line is short, and isn't near anything else, then higher is fine, it saves a little power. You can also work this from the other side, which is why you see so many different choices. If I can limit the current in the nearby line, then it will have a harder time making this line move. So if I can keep everything in the vicinity to very low current, then this line can work at very low current, too. But as you can see, in 99% of the cases, the value is terribly non-critical. Pretty much anything will work. I happen to like 4.7K. But if I'm already in my 10K drawer, or my 47K drawer, I'll use that. I gotta admit, if I'm pulling the line to ground through a contact closure, I'll probably lean a little higher, and if I'm doing this a bunch of times, I'll also lean toward the high side, in the interest of power consumption. Now, if I'm doing something to run off a battery, I might be a little more careful. A milliamp here and a milliamp there tends to add up. But most of the time, almost anything you lay your hands on will work just fine. --McD -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist