AVR-Chat

On Thu, Jun 17, 2010 at 07:52:49AM -0600, David VanHorn wrote:
> > The ATMega16's datasheet shows that the I/O pins have diodes from
> > the pin to Gnd and Vcc. ?These would seem to protect the pin from
> > surge voltages less than Gnd or greater than Vcc but I do not see
> > any specification as to what the max current capability of these
> > diodes is.
> 
> They do tell you not to put any current through the protection diodes.
> From a practical POV, I'd want to stay in the low microamp range..

Go look for an Atmel app note on direct reading voltages from AC power
lines. Might have been one on building a power meter for AC. The app
note I'm thinking of showed a 1M high voltage resistor directly
connected to 240 VAC or 460 VAC and an AVR I/O pin relying on the
protection diodes in the AVR.

It went on with a disclaimer that there was no advertised spec as to
what those diodes could handle but 1mA was thought to be safe, and
directly connecting the CPU to AC was a bad idea if it also connected to
humans.

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
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Whom computers would destroy, they must first drive mad.