This simple circuit is able to detect signal from your cellphone antenna and converts it to electricity to power an LED ( the best thing about this is that its completely passive and doesn't require batteries ) this circuit requires: RF diode ( search ebay for: RF diode or microwave diode) LED Peace of wire Solder I have Noticed that it only detects phones working on (EDGE), ocasionally works on 3G I have a low knowledge about RF but I think it has to de with the shape and/or length of antennas. So if you can contribute to make it work better please do so. ( this is based on a video i saw a long time ago on you tube ) the video had no instructions. here is the link http://www.youtube.com/watch?v=CNJVhzOjWgU&playnext=1&list=PL8ACFDE47FA548451 (RF energy, LED, tesla, passive, electricity)
Step 1: LED+RF Diode
First Solder the led parallel to the Rf diode
Step 2: RF Diode+ LED+ Wires
Solder One peace of wire to each end of the RF diode which will work as antenna
Step 3: Make a Call and Put the Circuit Next to Phone
The LED should Light up if the circuit is close enough to the phone while making a call.
I noticed that this works only if you are on EDGE .
If you are on 3G it only works occasionaly and the LED is very DIM