Hi,

Refering to Microchip's AN521, it shows a PIC connected to AC supply
line (of "several hundred volts") using just a 5 megaohm resistor in
series in between. Safety issues apart, it looks too simple to be true.
Is this enough to detect a zero-crossing (eg. for a PIC based triac
dimmer)or   should I put two clamping diodes on the pin detecting the
zero-crossing? I'm using a PIC16F870. I've read the manual and I believe
it doesn't have protection diodes in its i/o pins.

                              --->|---o Vdd
                  R           |
 240VAC o-------/\/\/\---o----o---------o PIC i/p
                 5 M     |    |
                         |    ---|<---o Vss
                         \
                     R   /
                    100K \
                         |
                         o
                        Gnd

Btw, the PIC in my dimmer is powered from a transfomer on the same AC
line (and bridge rectifier) so both the commons are going to be same.

Off topic, sitting here in India I can only guess what is "HOT OUT" and
"HOT IN"... its LINE and NEUTRAL, right? Pity we don't have such
interestingly graphic lingo down here.

Mohit.

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