[sdiy] filtering

[media at mail1.nai.net]

At 2:34 AM -0800 02/03/02, Toby wrote:
>hey guys
>
>i'm having a hell of a time making my divide by two circuit work.  What do
>you guys use for filtering on a digital chip?  I've been using .01 up to .1
>across the power supply pins.

For bypass caps??  I'm no EE, but I use .1uF (also called .1mfd, 104, or
100nF) ceramic caps.  I don't don't know if ceramic caps are better in any
way, but they are the most economical.  My only exception to this is the
555 timer, which has a huge switching transient.  For that I use a big
tantalum.  An elctrolytic would work fine, but I already have a bag of
tantalum caps to go with my sleeve of 555's :)

>I'm suspicious that there's a hell of a lot
>of interference where I'm located (60*n cycle especially).

I wouldn't depend on the bypass caps to filter the line.  Firstly, I run my
mains through a hefty LC filter and use an isolated ground.  Secondly, I
would use a power supply with adequate filtering and regulation.  You can
either buy one already made (which is probably the best and easiest
solution) or you could build one, or compromise and use a DC wallwart with
a three-terminal regulator with a couple extra caps.

Another thing you may try is running your circuit off of a battery.  If it
still doesn't work, then line hum isn't the problem.