Mobile (Cell Phone) led flashers

[abu]

Hi,

Can anyone explain how those led flashers on mobile phones work?
I'm on about those sticky backed types you glue onto the back of the mobile so when it rings the leds flash.

Thanks All
Abu

[Bigglez]

Greetings Abu,

Can anyone explain how those led flashers on mobile phones work?
I'm on about those sticky backed types you glue onto the back of the mobile so when it rings the leds flash.

The mobile phone transmits a data burst before it
rings (so that the cell knows the phone has been
located).

The LED is powered by the RF signal, and uses an
LC tank circuit to rob energy from the RF signal
to light the LED. The first one of these that I saw
was a spiral inductor that clipped over the phone's
antenna. Later I found one that had internal
batteries, and a keychain. It was sensitive enough
to flash if the phone was in another pocket.

Comments Welcome!

[Dave Dixon]

Here are a couple of schematics. I haven't tried them!
http://www.techlib.com/electronics/cellhelp.htm
Hope this helps,
Dave