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

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