>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@spam@mit.edu]
>Sent: 14 December 2005 16:00
>To: Microcontroller discussion list - Public.
>Subject: [EE:] Detecting a blown lamp
>
>
>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