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little car accessory that light up with cell phone usage

At the local autopart store, they have these little "toys" that clip
onto your car air vents. When you receive a call, the toy blinks or
lights up. How does that work? I'd like to build one myself.
Jeffrey
 
J

Jeroen

Jan 1, 1970
0
At the local autopart store, they have these little "toys" that clip
onto your car air vents. When you receive a call, the toy blinks or
lights up. How does that work? I'd like to build one myself.
Jeffrey

when you cell phone is being called, the cell phone sends information back
to the network. This a few watts worth of RF power. The 'toy' uses a filter
tuned to the right frequency, and because the transmitter is very close by,
there is enough power to light up a LED.
 
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