Tim,

you can do that when the light is off by connecting 10 meg resistor + 
diode after your
light bulb where it gets connected to triac to one of pic pin.
make sure your light bulb is connected to HOT wire
software function:
1. turn off the light thru pic
2. check thru resistor logic 1 ? 
3.  if it is 1 then the bulb is there 0 means open
4. if 1 turn the light on
5. check thru resistor again if  0 it means it is working if 1 your 
triac is open
now you can check if your traic is working too

Andre Abelian




Tim ODriscoll wrote:

>Hi Everyone,
>
>I'm making a little PIC-controlled floodlight interface for my house,
>and I'd like the PIC to be able to detect if the lamp filament is
>working.
>
>The PIC is running off a 7805 from a wall-adapter, and is happily
>controlling the floodlight via a triac. The floodlight is running off a
>240vAC fused spur and is rated for 500W. I have another floodlight I'd
>like to use for a second interface that is 250W, so I'd like to be able
>to create a 'generic' broken-filament detector that doesn't rely on
>there being a specific wattage of bulb.
>
>I've seen the X-10 Microchip app note where they just use a mega Ohm
>resistor to connect a PIC pin up to the mains for the zero-crossing
>detect, but I'm not sure on the safety issues of that one.
>
>My other idea was a transistor with it's base connected via a suitably
>sized resistor to the 240v live just before the floodlight. The
>transistor would drive an optoisolator. I've seen something similar on
>piclist.com describing a stalled motor detector, but I've no idea if it
>would work with a lamp of variable wattage at 240vAC.
>
>Any thoughts/ideas appreciated.
>
>Cheers,
>
>Tim
>
>  
>

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist