What is the theory behind these LED cell phone stickers?

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
107
They are shown in this video:


What is the theory behind these LED cell phone stickers? Is there a way I can make them myself at home? Maybe not in those cartoon designs but a small LED which lights up when I place it near a phone and call it.
 

ZCochran98

Joined Jul 24, 2018
305
When you make or receive a call, you are generating electromagnetic waves of a specific frequency range (what range depends on the generation of cell service). You can capture some of those waves via antennas (and, in this case, they're designed to be 2D meandered microstrip antennas whose total length is either 1/2 or 1/4 the signal wavelength each - probably 1/2, I'd guess), and use what amounts to a very rudimentary rectifier circuit to convert the captured signal to a (small) usable amount of power to the LEDs. At 7:42 in the video he gives a perfect schematic of it, which could let you, in theory, design one. However, the antenna design can be a bit tricky, as if you don't tune it to the right length, it won't work.
This MAY cause a little signal degradation, due to "bleeding off" some of the power transmitted/received to power one of these things.
 

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
107
They most certainly will bleed off your wallet
How? What would be the price of SMD components to make it?
That theory of operation is that a fool is born every minute.
Elaborate.
When you make or receive a call, you are generating electromagnetic waves of a specific frequency range (what range depends on the generation of cell service). You can capture some of those waves via antennas (and, in this case, they're designed to be 2D meandered microstrip antennas whose total length is either 1/2 or 1/4 the signal wavelength each - probably 1/2, I'd guess), and use what amounts to a very rudimentary rectifier circuit to convert the captured signal to a (small) usable amount of power to the LEDs. At 7:42 in the video he gives a perfect schematic of it, which could let you, in theory, design one. However, the antenna design can be a bit tricky, as if you don't tune it to the right length, it won't work.
This MAY cause a little signal degradation, due to "bleeding off" some of the power transmitted/received to power one of these things.
What SMD do you suggest I could use?
 

BobTPH

Joined Jun 5, 2013
9,296
That depends on whether you want it to do nothing like the old ones, or have them light up with current phones using 5G.

Why not design an antenna and rectifier and measure what voltage and current it can produce before choosing parts that might or might not work?

Edited to add: And if you are hoping it will protect you from imagined dangers, just throw in anything you want, they will all be equally effective.
 

BobTPH

Joined Jun 5, 2013
9,296
Because it will still protect him from brain tumors caused by cell phones. Haven’t you heard of the global epidemic of brain tumors since billions of people have started using cell phones? Oh, that’s right, the illuminati have suppressed the news. The truth is out there!
 

MrSalts

Joined Apr 2, 2020
2,767
Because it will still protect him from brain tumors caused by cell phones. Haven’t you heard of the global epidemic of brain tumors since billions of people have started using cell phones? Oh, that’s right, the illuminati have suppressed the news. The truth is out there!
Excuse me? I don't understand sarcasm since my brain tumor surgery.
 

Thread Starter

bypassrestrictions

Joined Jun 1, 2021
107
That depends on whether you want it to do nothing like the old ones, or have them light up with current phones using 5G.

Why not design an antenna and rectifier and measure what voltage and current it can produce before choosing parts that might or might not work?

Edited to add: And if you are hoping it will protect you from imagined dangers, just throw in anything you want, they will all be equally effective.
I want to create one which lights up for contemporary smartphones in India, I just have to find the most common frequency in use and make 1/2 wavelength and 1/4 wavelength antenna for that.

Why would you want to make one when modern phones (4G and 5G technologies) won't light them up?
I think I just have to change the antenna length to make them work for contemporary smartphones.
 
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