Using 74xx574 D FF to expand PIC outputs

Wasn't this for an optical display?

robert

Sure. But it sounded like "light show" and that's often done in conjunction with some kind of concert. Meaning long cables, rolled out by people who don't have the foggiest idea about EMI, stuff coupling over into the audio gear and so on.

Though it's not for a "light show" per se, it will be attached to (and controlled by) a PC that is also producing sound, and the roadies I imagine you're talking about are really just home PC users (equally clueless about EMI), so this is in fact something that will probably require consideration...

Many of them sure are blissfully unaware. I tried several times to convince a guy who had lots of noise in his audio to invest a few bucks in an audio transformer, explaining that the switcher of his laptop was causing the noise. Weeks later he was still wrestling with the problem, trying to get by using the battery. Did he go to Radio Shack and buy a transformer? Nope.

I agree here too - whenever I use a protoboard, I load it up with caps. If there's a chip I can't straddle with a cap, I'll put one at each end, from Vcc to Gnd:

---------+---------------+--------------

Good to know! I got lucky this time: The PIC's Vdd/Vss are directly across from each other, and the 574s have an active low enable pin directly across from Vcc, which I then jumped to ground. But I'll probably do what you've done once I get around to ordering that veritable bucket of .1uF ceramic caps...

Thanks PSM