Electromagnetic Flashing Stickers

[rahul986]

Hi,
Recently I've been seeing certain objects called as Electromagnetic Flashing Stickers. They are also named as Mobile Anti Radiation Stickers. I've tried a lot to decode the circuit but in vain. The sticker works something like this: It has to be at stuck at the back of an Internal Antenna Mobile phone(like Nokia 3310,3315). Whenever we receive a call, before ringing itself the sticker with two to three LEDs inside it starts flashing. It flashes even when messages are received. I would really be pleased someone could help me out with the circuit.

That was the question I asked in my previous post. But someone replied thinking that there was a wire attached from the cellphone to the mobile. Infact there is no connection between them except for a contact.

 

[evandude]

put your cell phone next to your computer speakers sometime and then call it from another phone. or try setting it right below a CRT monitor. you'll hear some interesting sounds, or see some interesting distortion. There's a lot of energy coming from a cell phone when it rings. I would imagine something as simple as a coil made with a lot of turns of fine-gauge wire would be able to pick up some reasonable signals from it. perhaps the sticker has some form of coil in it (probably flat copper film) that acts like half a transformer, picking up the energy from the phone, thus inducing a voltage in it that is enough to light up some small LEDs. you probably won't get much current out of it but for small LEDs that's not much of an issue.

 

[grrr_arrghh]

i have a phone holder that flashes when it rings. It also flashes randomly, because phones identify themselves to the cell from time to time, and this is picked up by the flashing thing. Mine has a small button battery to give enough power to the LEDs, the coil only has to trigger the flashing.

 

[rahul986]

Please read this update

What you people said is indeed correct. The sticker contains a small strip line antenna and two LEDs with a small black object which I believe is an operational amplifier. I request you to visit the following website: **broken link removed**
This website contains the front picture of the stickers I am talking about.
Coming to those stickers which work with a battery, I guessthe wave triggers a circuit. If possible can anyone post the circuit for it. :?:

 

[Nigel Goodwin]

Re: Please read this update

What you people said is indeed correct. The sticker contains a small strip line antenna and two LEDs with a small black object which I believe is an operational amplifier.

I would suggest that the small black object is more likely to be a rectifier, there's no reason to have an opamp.

 

[rahul986]

So any idea for the circuit. The signal is recieved by the strip line antenna and then rectified is what you are saying. Do you think any amplification is taking place or do you think what is being recieved is sufficient to light up the lower power LEDs.

 

[Nigel Goodwin]

So any idea for the circuit. The signal is recieved by the strip line antenna and then rectified is what you are saying. Do you think any amplification is taking place or do you think what is being recieved is sufficient to light up the lower power LEDs.

You can't amplify the signal without a supply voltage, but there's no need to, a simple coil should pick up enough voltage to light the LED's at such close range. Presumably it's not accurately tuned, as phones operate over a wide range.

Interesting marketing ploy in the advert, claiming they reduce radiation :lol: they are just as likely to do the exact opposite, if the minute amount of power absorbed by the LED circuit reduces the field strength from the phone it may increase it's power to compensate.

 

[rahul986]

You are right. The other day I was having a discussion with one of my friends. The Anti Radiation thing is just to boost his sales. But it doesn't matter to us in anyway. We are just trying to analyse the circuit. I'll try building the circuit with the components we observed.

 

[Nigel Goodwin]

You are right. The other day I was having a discussion with one of my friends. The Anti Radiation thing is just to boost his sales. But it doesn't matter to us in anyway. We are just trying to analyse the circuit. I'll try building the circuit with the components we observed.

I would suggest the coil is the critical item, probably as well to copy it exactly!. Also the rectifier will probably need to be suitable for the high frequencies in use.

 

[Oznog]

It may not need a rectifier since the LED is a diode by nature. But there's probably an IC for timing the flashes in an attractive pattern which needs a DC voltage. Sometimes that's integrated into the LED case, in which case the LED needs constant DC.

 

[rahul986]

Hmm i've done a mistake. I've mistaken that black object to be an op amp instead of an IC. That IC infact controls the lighting pattern because there are many stickers with different lighting patterns. So updating the precious post the wave is to be recieved through a strip line antenna and then? Something has to be done. Then its output has to power the LEDs. So what could be possibly done for that something?

 

[grrr_arrghh]

is the black dot on of these small curved shiny black dots?
if so, finding out what is in it may well be very difficult. Are you sure there isn't a small battery in there somewhere?

As for the radiation thing, it would only be of any use if the metalic bits blocked the radiation, which if you have it on the back of your phone, all it will do is bounce the radiation back to your head!!

 

[rahul986]

Yes i'm sure. I've attached a picture of the sticker. It is not that clear. But you can see the small black spot at the lower right corner. You see it is not shining. It is definetely an IC. And then there is a small projection which I think is the reciever. The IC has two solders on either side.

 

[Clyd3]

Keep this topic going!

I was just about to ask about this thing on the back of the phone when I got online. Are you really gonna try make it, awesome!
I think you guys are right about it so far, at least as far as I know...
The diodes themselves probably do the rectifying, and the black thing probably does only make the pattern the lights flash with, but doesnt that mean that you could probably make the circuit without the black thing, and the diodes wouldnt flash?
If so, THATS AWESOME!!!!
I love this kind of thing(reasons to have a happy day...)

 

[rahul986]

Thanks for the interest Clyd3. According to a personal discussion with Someone Electro(Electronics Expert) in another thread this was what has been figured out:
The two LEDs(as in the case of the normal and cheap stickers. Actually this number can be as high as 8 also) are low curent LEDs. In this sticker there is a stripline antenna that suks up the RF energy transmited by the phone and leads it to the LEDs. It can get up to 1-2 mA of energy form the phone.

This proves that phones can produce a lot of RF energy.
Now the problem is without the IC we have to build the circuit that consists of the following components:
1. Strip line antenna(for the smaller size of the sticker)
2. Two or more LEDs(If you see the picture I attachedd above there are around 5 LEDs) - these LEDs alo act as rectifiers probably
3. An IC to control the flashing pattern. If this is not present all the flashing takes place in a unique pattern - all lighting up at once.
4. .........................................
I can't think of any. If anyone thinks of a much better design please update the above design sequence.

 

[Clyd3]

Nice

Thanks a lot, I want to try this very soon.

 

[Someone Electro]

You cod try making a coil of wire thin wire and conecting a low curent led to it.Stick it to a phone and try to make a call.

 

[rahul986]

I could find LEDs which work @ 2mA. I guess this would be sufficient. I buy one and do as you said.

 

[vaineo]

What size coil would you be using, are you talking about using hundreds of turns or just a few?

 

[Someone Electro]

I think 30 thurns shod do.Here the biger the beter is NOT true.Becose if you use a to big coil it will have an to high inductace wich will mean it codnt pick up the high freq. radio signal so well.So if you try to make a realy big coil you have to keep the inductace of ti to the minimum.

Try eksperemantig whith the coil!