[sdiy] unused pins ?

[harry]

Harry will throw in a related story...

When you tie CMOS inputs high, or low... be sure you do
no tie any OUTPUTS by mistake.

Outputs should be left floating....

Finding a shorted unused output is very hard. The last place you look
in a non-functional circuit is the gates that are not used. You will be lucky

if you probe there. I found one because the chip was slightly warmer than the
rest...

H^) harry

Magnus Danielson wrote:

> From: Mountain Man <mtman at cloud9.net>
> Subject: [sdiy] unused pins ?
> Date: Sat, 07 Apr 2001 10:53:19 -0400
>
> > Hi folks,
>
> Hi there...
>
> > I'm breadboarding my first "non-pcb" circuit and I'm
> > wondering what to do with the pins that are unconnected?  Specifically,
> > the S/H from tomg's sbm doesn't seem to use the offsets on the TL071,
> > but I'd like a general answer to this question :)  Do I leave them
> > unconnected?
>
> Yeap. You should.
>
> >  Connect to ground?  Does it depend on the particular
> > circuit?
>
> It most particularly depend on the chip. For logic gates and
> especially CMOS chips you should wire all inputs to either high or
> low, they should never be allowed to be floating. For OPs you should
> check the datasheet carefully, but for things like offset and
> compensation inputs it is most commonly so that you may leave them
> really unconnected.
>
> Except for logic chips, you should find hints in the datasheets, for
> logic chips you may have to look in the familly description documents
> in order to find the necessary sentence.
>
> Leaving floating CMOS inputs around can be a HUGE misstake!!!
> I guess Harry could toss in some nice story on it, I don't have one
> that springs to mind at this moment...
>
> Cheers,
> Magnus