Re: Can I do this with a uProcessor?



Spehro Pefhany wrote:

Eeyore wrote:
Spehro Pefhany wrote:

Wiring switches directly to I/O ports is a really bad idea.

Why so ? They're simply pulling to ground. There's no external connection to >worry about
here.

Any kind of ESD through the switch that that doesn't get shunted to
ground can cause a CMOS processor to latch up, and likely die. There
will be fingers on the switches, and static electricity. A 0.1 cent
resistor is cheap insurance. Same deal if there is a difference
between ground potentials, for example caused by a motor-driven volume
control pot).

There's no practical path for ESD between say a TACT type switch with its mounded on keytop
and the internal circuitry. If someone's sufficiently charged with statis for it find a apth,
a little ressitor isn't going to save anything !


I've lost count of how many tens of thousands of products doing exactly this must >have
been made for Studiomaster. Problems, zero.


Maybe they were properly designed

By me !


taking into account ESD, or maybe they were lucky that the design turned out to be okay, or
maybe they didn't analyze the failures.

Where's the ESD path ?

It's this kind of switch......
http://uk.farnell.com/jsp/Electrical/Switches+&+Accessories/ITT+CANNON/D6C90LFS/displayProduct.jsp?sku=1201367

The keytop is located in an aperture in a grounded steel panel.


Graham

.

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