> I'm sure there are several other ways to accomplish this and could use 
> your recommendations. To recap, I want to detect when a bulb is in a 
> socket using the filament as a switch. I will use a PIC pin to monitor 
> this and will use another PIC pin to turn the light on/off. The light 
> will be an incandescent type operating at 120VAC and be rated at 25W.
>
> Thanks in advance.
>
>
>   
One could use the PIC to generate a high frequency square wave using the 
PCM module. Then couple this to the AC line via a small value blocking 
cap and measure the injected signal level with a diode detector and the 
PIC's ADC. Presumably the injected high frequency voltage will differ 
whether the bulb is in place or not. Might need to isolate the bulb from 
the rest of the house wiring with an RF choke, however, as otherwise the 
total impedance of the wiring plus other devices will vary as loads are 
added, switches thrown, etc.

A variant on this would be to inject a high frequency current into the 
line via a current transformer and measure it.

Appropriate caution needed when selecting components that connect to the 
line, of course.

Jack
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