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LED mobile flashing antennas? — Parallax Forums

LED mobile flashing antennas?

john_sjohn_s Posts: 369
edited 2008-12-04 18:32 in General Discussion
I wonder if anybody knows how do these work?

http://www.calcellular.com/flash-ant-blue.html

They also come in a form of "LED mobile phone stickers"

http://highrich.manufacturer.globalsources.com/si/6008817535084/pdtl/Sticker/1002091183/LED-Mobile-Phone-Sticker.htm

I cannot see any internal batteries - so what's the circuit schematic?
Perhaps the rf charges some kind of circuitry (flat supercap?) that delivers enough juice to flash the LED?





Post Edited (john_s) : 11/18/2008 5:11:07 AM GMT

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-18 05:28
    You got the idea ... There's a small antenna, diode, and filter capacitor that charges when there's a signal present from the cell phone. When the voltage across the capacitor gets above the threshold needed to turn on the LED, a transistor switch discharges the capacitor through the LED flashing it. There are all sorts of micropower LED flasher circuits available on the 'net that draw microAmps at low voltage.
  • john_sjohn_s Posts: 369
    edited 2008-11-18 17:53
    Thanks Mike,

    What always puzzled me was a·"warning" statement that those gadgets were supposed to be used with GSM devices only... How about a dual-band antennae to pickup up CDMA-bands as well? Any help on this...
  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-18 18:09
    What kind of help are you asking for?

    I don't remember "warning" statements, but there are several frequency bands used for cell phone transmissions (from handset to tower) and you'd need a multi-band antenna to cover the various types of handsets.
  • john_sjohn_s Posts: 369
    edited 2008-11-18 20:31
    Four to be exact - 850, 900, 1800 and 1900MHz - (and out of the 4 freq's just·2 are of any value for the sake of the LED flashing circuitry; i.e. the Tx freq's from the mobile phone only...) so within the range of two dual-band antennaes (slightly de-tunned mind you) one should be able to cover any CDMA·or TDMA "LED-flashing" gadget... or am I wrong?

    p.s. to Mike - the "warning" says CDMA Phone Might Not Flash!

    Post Edited (john_s) : 11/24/2008 3:23:20 AM GMT
  • GICU812GICU812 Posts: 289
    edited 2008-11-18 21:05
    And pop popcorn at that!!

    :Rolleyes:

    The public is sooo gullible..
  • TeslaTesla Posts: 55
    edited 2008-11-21 21:01
    I wonder how much transimit signal you lose by putting one of them on a phone if some of the power is going to light the LED.
  • john_sjohn_s Posts: 369
    edited 2008-12-03 06:00
    Tesla,

    Quite considerable according to this:

    http://www.bakom.admin.ch/themen/geraete/00568/01229/index.html?lang=en

    ·
  • TeslaTesla Posts: 55
    edited 2008-12-04 18:32
    john_s

    Thanks for that link I always wondered from the first time I had seen one.
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