On 20 Oct 2016 at 16:33, Van Horn, David wrote:

> I am mainly just thinking out loud here.  Understanding that some of
> you prefer to "short outputs" instead of using weak pull-ups, I
> nevertheless am curious as to your design thinking at times when you
> actually do want to use a weak pull-up to minimize current yet avoid
> serious EMI issues.  Or do you just go about selecting weak pull-ups
> via "trial & error"?=20

Ball park figures I generally start with for external pull-ups:
- 47k or 100k for short traces on a PCB when consumption matters
- 10k anywhere on a PCB when consumption doesn't matter
- 470R to 2k2 off PCB

Of course anything will work... engineer/test/refine to obtain "acceptable=
=20
workingness" for the application, plus some margin.

> If it's a one-off for your amusement, then do what you like.=20
> Especially if wrong operation has little to no consequence.=20
>=20
> The products I am currently designing are life-or-death.  I don't
> even have dipswitches.     The three switches I do have, have pull
> resistors that are activated just before reading, and a series
> resistor between the switch and the micro for ESD.   A small
> capacitor at the micro pin smooths the input, and that ESD resistor
> also limits current between the cap and switch, keeping me from ever
> exceeding the switch current rating.  I mostly use the controlled
> pullup scheme because I have to have a very long battery life.

Good thinking. Do you also keep the pin an output and low untill you need t=
o read=20
the switch? In a worst case (induced noise) scenario it would keep the volt=
age on=20
the pin from floating around and possibly entering the analog region causin=
g=20
unwanted consumption or mis-operation.=20

> Current wasted into switches during the 999mS when I'm not looking
> is just stupid.   The impedances are low enough that we pass ESD
> without upset, and radiated susceptibility which is normally tested
> at 3V/m for this type of product, will still pass test above 150V/m=20

I'm not surprised it wates current: 999mS =3D 1.001 Ohms ;-)
https://en.wikipedia.org/wiki/Siemens_(unit)

> How normal people test for ESD Issues:  http://www.teseq.us/products/NSG-=
435.php
> How I test for ESD issues: https://www.youtube.com/watch?v=3D999gLBK77ss
> After it passes my test, then it gets formally tested by the first
> method.   Funny thing, I have never failed formal ESD testing.=20

Nice. I usually just contrive something: Find a suitable inductor lying aro=
und=20
(transformer), add some caps to a DC power supply, wrap some turns of wire=
=20
around the device under test, touch contacts together and get some arcing g=
oing=20
on.
=20
> I've always said that embedded systems should "Just Work".  Meaning
> that you shouldn=B4t have to even think about it, operation should be
> obvious, and it should be dead reliable. If your new toy from china
> doesn't work right, you get annoyed or maybe inconvenienced.  The
> products I'm designing now, if they don't work, someone dies.=20

Absolutely. My other dis-like is embedded systems that take too long to boo=
t up,=20
some as long as 45 seconds. My "smart" TV annoys me in that picture and sou=
nd=20
come up quick enough but response to the IR remote to change chanel is flak=
ey=20
(ignored, or accepted but delayed) until about 10-15s after switch on.




--=20
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