How does a cell phone detector work and how to build one?

Thread Starter

gloface

Joined Apr 15, 2007
2
Do you know those cell phone detectors that has LEDs that flashes when there is an incoming call? Something similar would be this pen that i found through google (the link originally provided expired, the redirection was to a suspicious site - moderator). I would like to find out how these work exactly and how to make one of my own.
 

Thread Starter

gloface

Joined Apr 15, 2007
2
but what im having in mind is different. what i want is the detector that is able to convert the energy that is broadcast by the phone when it is active to light up the LED. In other words, it is operable without batteries.
 

beenthere

Joined Apr 20, 2004
15,819
Don't think there is enough energy available for such a device. A crystal radio can get just enough poop from an AM broadcast pumping out thousands of watts to drive a high impedance headphone. Your detector would have to build at least 1.5 volts and 2 - 5 milliamps to light a LED. The cell signal is in the milliwatt range.
 

mozikluv

Joined Jan 22, 2004
1,437
i know what he is trying to imply. that led is the one used as backlight to keypads of a cellphone. this device is coated with rubberized plastic with an adhesive to be pasted at the back of the cp, near the antenna. but i have never given it a thought how its done coz its sold here at $o.o5 a piece only. so every time a signal comes in/out it lights up in a blinking fashion. some of those uses 3 - 4 leds so it looks like it dances.

moz
 

Papabravo

Joined Feb 24, 2006
13,712
They still don't light up without using the battery. There is just not enough RF Power to make it happen. If there was it would be heating up your eyeballs and other things as well.
 

Papabravo

Joined Feb 24, 2006
13,712
OK -- if you guys are convinced that power to light something can come from the ether it's fine by me, but I'll remain skeptical if it's all the same to you gentlemen.
 

Papabravo

Joined Feb 24, 2006
13,712
Why would you believe we think the power comes from anethesia?:confused: The power comes from the cell phone's transmitter.
Whose power comes from where exactly? With an efficiency of what? Why not just connect it to the battery? Why mess around with such an inefficient scheme? This reminds me of a solution looking for a problem. BTW was I supposed to discern that from the pictures of the fuzzy bowties?
 

thingmaker3

Joined May 16, 2005
5,084
Why not just connect it to the battery? Why mess around with such an inefficient scheme?
Its an after-market toy. Connection to the battery would require different configuations for different cell phones. Using the less efficient method, one size after-market toy fits almost all cell phones. Target market cares more about style and fasion than about efficient battery use.
 
I've got a antenna for my Nokia 5190/6190 that flashes when the phone is transmitting/receiving. Its old now, but I took off the antenna and put it next to my PDA phone and it still worked :)
 
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