Disco lights on mobile phones ?


I’ve noticed quite a few girls with mobile phones that have little disco / fairy lights that flash when they are using the phone. It seems they have stuck on “thingies” with very small basic circuitry and tiny LED’s on the phone casing that flash when the phone is in use.
How do these things work? Where do they get the power from? Do they use transmitting power thereby the affecting the range of mobile cover?
I have also seen flashing antenna on some mobile phones that still have them I guess this is the same kind of thing.
I remember some time ago with CB radio you could get a ‘Wally” light for your antenna that would light up when you used the CB. But this was not very popular as it was thought to reduce the TX power. Is this the same kind of thing?

Just Curious me!.

My fiance had one a while ago. I can’t say if it decreased the transmitting power, but it drained the holy heck out of the battery.

Just a simple relaxation oscillator circuit for each light. Such a do-dad needs a separate battery.
It is just another airhead novelty to add to the battery load on the phone and contributes nothing to enhance the purpose of having a cell phone in the first place.
My view is that if you really need all of the extra funcitionality that bad you need the real thing to do the job that is done half-fast by the add-on featue.

So how exactly do they work??? If you’ve ever looked at them, they really have no way of knowing when the phone was ringing. In fact, they even make some that are just keychains. I believe those were marketed to high school/college kids. It let them keep their phones in their backpacks or purses and just keep a set of keys up on the desk.

Every cell phone sents out an acknowledgement signal in response to an incoming ring signal from the cellular network. The keychain ring detectors simply pick up this signal and make some LEDs flash. The passive flashers as found in those flashing antennas don’t need a battery–they get their power from the RF output of the phone, but the ring detectors do need their own battery, AFAIK.

Yes! Erm! But where do they get the power from? The ones I have seen work not only when the phone rings but all during a conversation. Obviously triggered by the Tx/Rx but I don’t see any battery in with the light circuit so the question remains do they get power from TX thereby reduce the range? :confused:
I agree it’s just a gimmick but the girls here seem love then specially when they are out in the evening and the lights really show up.

They draw power from the RF signal being generated by the phone; in practical terms, this means that the signal that actually ‘gets out’ is attenuated - it has to be.

In the case of those ill-concieved ‘radiation shield’ devices (the ones that supposedly protect you by blocking your phone’s RF emissions) cause the phone to ramp up the output power, but only because they also block incoming RF signals, making the phone think it is in an area of weak coverage.

In the case of the flashing stickers, they are powered by the outgoing RF (which is why they only work if they are really close to the antenna) - unless the network has a means of reporting low signal levels back to the phone, there would be no way for the phone to know that the outgoing signal was being leeched and this could result in poor performance.

I don’t know how noticeably this translates into reality - I had a flashing sticker on my last phone (I took it off because I couldn’t make or receive calls discreetly - even on ‘silent’ mode, the thing is still set off as soon as the thing receives a call), I didn’t notice any significant loss of performance, but without an identical, unstickered phone alongside, objective assessment would be hard.

Specifically, part of the miniature printed circuit inside the sticker is an antenna; this antenna generates a tiny amount of current in response to RF signals (RF signals ‘are’ power) - this alone is not sufficient to light an LED, so it is fed through a charge pump circuit, which stores it up and emits it in very short pulses of sufficient power to drive the LEDs (and whatever additional circuitry is required to sequence the flashing).

That just about covers my original question - Thanks to all. :slight_smile: