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Recently, an old mobile phone inoperative fell into my hands. As a result, it was disassembled for parts. A train of an interesting form with smd components did not slip out of sight. As a result, without thinking twice, I decided to make a radio bug on a flexible board. I chose the simplest scheme for the beetle, since the beetle did only as a trial version.

Flexible radio beetle


A microphone amplifier with a low-power transistor was added to the circuit to increase the sensitivity of the microphone, but as it turned out in vain, since the difference with the amplifier and without it was negligible, therefore, for your consideration, I propose a circuit without a microphone amplifier. This is perhaps the simplest of all known schemes. The transmitter is made on only one transistor of the CT 368 series. The circuit contains 5 to 6 turns of wire with a diameter of 0.7 mm. The antenna is a piece of wire with a length of 8 - 10 mm (if you make the frequency longer), the microphone is the most ordinary, it was removed from the same phone. Electret microphones in themselves already have one amplifier stage, therefore they can provide sensitivity up to 5 meters without an additional microphone amplifier.

Flexible radio beetle

Flexible radio beetle


After checking, the circuit was transferred to a flexible board. The beetle is assembled using smd components, but for beginners I advise you to use ordinary radio components to begin with. The range of supply voltages is from 3 to 9 volts. It is very convenient to feed the bug from the crown with a voltage of 9 volts. The current consumption is not more than 9 mA, that is, an ordinary crown lasts for 3 to 4 days of continuous operation of the bug.

Flexible radio beetle

Flexible radio beetle


The device remains operational even when the supply voltage drops to 2 volts. True, the range of the bug turned out to be small, only 40 meters with direct visibility. Caught on a Chinese receiver for 150 rubles.
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Comments (10)
  1. alex
    #1 alex Guests June 8, 2012 12:38
    0
    Which AF, AE signal is transmitted?
  2. Dmitry Vladimirovich
    #2 Dmitry Vladimirovich Guests January 7, 2013 18:44
    0
    In his youth he did almost the same as a coven. KT368 is the right choice, but with a similar scheme and in such a layout, the stability of the carrier cannot be ensured - I did so. Three 1-sided signets 10x10x1 mm. On the first, I mounted an electret with a preamplifier, on the second - a circuit, on the third - an RF amplifier with a varicap. Assembly of three boards with a whatnot. Food - three elements of SC-21. Adjustment is reduced to finding the orientation of the loop coil with constant frequency tuning in FM. As a result, the stability was highest. The radius of reliable reception with an antenna of about 10 cm to a receiver with a sensitivity of 1 μV and a stationary antenna of about 350 m! Now to do such is no longer relevant - there are many other options.
  3. Vladimir
    #3 Vladimir Guests October 12, 2013 18:46
    0
    did exactly as it is written but the signal is not transmitted
    is wire thickness important?
    since I used 0.35 mm
  4. wowak
    #4 wowak Guests July 31, 2014 3:22 p.m.
    1
    And where do they say what I’m saying, I don’t understand?
    1. Seryoga
      #5 Seryoga Guests September 15, 2018 23:33
      0
      Big brother's tape recorder
  5. john85
    #6 john85 Guests December 21, 2015 08:24
    0
    It is transmitted directly to the surrounding space. Accepted by the radio. which is logical.
  6. Artur
    #7 Artur Guests February 24, 2016 17:21
    0
    And you can catch a signal from a mobile phone
  7. Alexander
    #8 Alexander Guests January 10, 2018 2:59 p.m.
    0
    Good afternoon.
    And tell me please, a capacitor based on a transistor with a face value of 0.1 why? nF, mF, pF?
    1. Gundyaev
      #9 Gundyaev Guests February 13, 2019 at 06:49 a.m.
      0
      0.1 is only mF, which corresponds to: 100nF
  8. Fedor
    #10 Fedor Guests July 14, 2018 2:56 p.m.
    0
    Collected, works on 93-102 FM. I can give it, I don’t need it, it was just interesting.

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