Does a transformer....pass these spikes?  I always assumed that because the
"transformation" of voltage was because of the magnetic coupling from
primary to secondary windings, that spikes were minimized.

-----Original Message-----
From: Anne Ogborn [mailto:anniepoo@NETMAGIC.NET]
Sent: Wednesday, July 14, 1999 8:39 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: Long-term timer


> Use a diode off one side of the mains transformer's secondary, through a
> largeish resistor, to a PIC pin, to detect AC cycles.  (Keep the current
> through the protection diodes low so you don't mess yourself up, by
> large enough resistor value.  100kish or so?)
>

uh, guys...
    There are some impressive voltage spikes running about on
the power lines. An optocoupler is a better solution, and you
presumably will need some isolation anyway at the output end
if it's to interact with a hum