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Today's 'what the heck is it?' item...

Discussion in 'Electronic Repair' started by William R. Walsh, Mar 29, 2009.

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  1. Hello all...

    I was cleaning up some stuff in the basement when I found a cardboard box
    with a Newsweek address on it. Opening it revealed a small white-cased
    device with an on-off pushbutton and a speaker. It uses 4 double-A
    batteries. There are no other controls or indicators on it anywhere.

    I first thought that it had to be some kind of a fixed-frequency radio,
    probably something that was tuned to one AM station for promotional purposes
    or maybe even a weather radio. But it doesn't seem to receive
    anything--assuming it even works. With batteries in place, it would hum
    (much like ground loop hum) and the sound would get louder near electrical
    wiring. I never heard any sort of station or static.

    Taking it apart revealed a very simple circuit board with a coil, power
    switch, a few small transistors, some resistors and a few caps. It's really
    very simple--too simple to be any kind of radio I'd know about. The one IC
    on it is an STMicroelectronics TBA820M audio amplifier, with a date code of
    early 1988. Running it while taken apart revealed a few things--let the
    circuit board get near the battery compartment or wires, and the speaker
    would go into feedback. The coil on the board was sensitive to touch or
    metal tools--and produced a "tapping" sound in the speaker when touched. It
    was not sensitve to other random objects on my workbench. I also found that
    I could feed audio into one of the connections on the coil and hear it
    clearly through the speaker.

    A picture of the circuit board is here:
    http://greyghost.mooo.com/newsweek-radio.jpg (541x255, 47KB)

    William
     
  2. Probablty a Stud Finder -- locates the nails in the drywall hammered
    into the stud.

    Jonesy
     
  3. Baron

    Baron Guest

    It could be an induction loop amplifier ! Used by people that are hard
    of hearing !
     
  4. Eeyore

    Eeyore Guest

    And finds where power cables are.

    Graham
     
  5. I have one of these things. The circuit board is identical to the
    one in the pic.

    At first, I did think it was some sort of telephone amplifier.

    But now I'm inclined toward the stud or wiring finder type of application.

    This is a small embossed arrow next to the on/off switch that lines
    up with the coil.

    Mine buzzes to some extent all the time, but is sensitive to ferrous
    and/or magnetized objects near the coil. It squeels in various ways
    depending on size, orientation, magnet strength, etc.

    --
    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  6. Well, that's what I had concluded (see my other posting). But now,
    I'm leaning back toward the amplified telephone idea.

    I placed it near one headphone from a Walkman and it did an excellent
    job of amplifying it with the Waliman set at very low volume and providing
    a fairly decent, if low fidelity, output from its loudspeaker. If even
    worked 3 inches from a cell phone!

    So, perhaps it's a multiuse device. :)

    --
    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  7. hr(bob)

    hr(bob) Guest

    Half of a baby minitor???
     
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