I've seen zero crossing detection of AC currents come up frequently on this
list lately, especially with respect to dimming applications.  What is the
practicality of zero crossing detection?


In a message dated 98-05-10 14:23:40 EDT, you write:

<<        Each pin has a clamp diode to ground and Vcc to limit voltage
 excursions to that which the chip will tolerate.  As long as you are
 using resistive loads that only connect to +5V and GND, you'll not get
 any current through the clamp diodes.  A favorite example of using the
 clamp diodes is to put a current limit resistor between the clamped pin
 and some higher AC voltage.  I typically connect a 10K between the INT
 pin and 12VAC to detect AC line zero crossings (see the Shoebox dimmer at
 http://www.dovesystems.com).  Microchip has an application note where
 they do this to detect zero cross by running a resistor directly to the
 120 VAC line.
  >>