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Discussion in 'Electronic Basics' started by [email protected], Mar 15, 2007.

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  1. Guest

    Does anyone not reading my other thread have any ideas what the power
    drain would be for a very small radio?

    I basically want an audible noise for as few milliwatts as possible,
    and run from a 12V lead acid battery.

    TIA jack
     
  2. The 'few mW as possible' and 'noise' suggests to me - piezo. A lot of
    them are spec'd for 12V, too. I think 5mA (maybe a little more) would
    be typical. So 60mW, roughly speaking. I think a custom design would
    be able to do better on power consumption -- but those figures are for
    off-the-shelf and very cheap designs (about $1.)

    Jon
     
  3. Guest

    Wow, thanks Jon.
    That's going to make things a lot less expensive and complicated.
    I could buy two, one for a spare :)
    Any ideas what they would be called and what sort of outlets would
    sell these? I will try a google search for Australia.
    Thanks, jack
     
  4. If you want to hear it I'd avoid piezo. Also, a bigger speaker will draw
    less power for a given sound output.
     
  5. Guest


    Thanks again Homer.
    All I can find so far are piezo earphones for crystal sets.
    Interesting about the big speakers. I've got plenty of them. Does the
    impedance affect the efficiency?

    To be honest, all I want is a bit of noise audible at the front door,
    that gives the impression of someone being home. A crystal set that
    received several close stations would be fine, and whatever speaker I
    used I would tape to a panel of the front door to act as a sound
    board. Afterall, no-one will be listening to the information or music,
    and especially not inside the house :)

    I thought I read somewhere about piezo being augmented with a horn.
    Perhaps attached to my door panel? If I can get some 24/7 noise with
    10 mA, I could run the thing for 4 weeks from a 12Ah battery with NO
    charging. So any charging would be cream on the jam, so to speak.

    Thanks again, jack
     
  6. Well, someone else thinks piezo are hard to hear. They use them in
    fire alarms a lot, so I have to disagree a bit on that point. However,
    they are higher freq (3kHz to 4kHz area) and if you have hearing
    troubles at high freqs, then they may be dampened a bit. Ambient
    environment can also make or break this.
    They are called piezo alarms or buzzers. You need to be a bit
    careful, though. Some piezos are sold without the driver circuit,
    depending instead on you fabricating one. Those will be the really
    cheap ones. You want those that are ready to go, I guess. Go to
    www.digikey.com and enter 'piezo' in the search. Then look down for
    'buzzers' and click that. You can then select frequencies or current
    draw, etc. and do a further search. Or google these three words,
    piezo buzzer 12V. That will get you some web sites to examine,
    selling them.

    Jon
     
  7. Guest

    Thanks Jon, I think I may have misled you with my term "noise". I
    really want the noise of habitation. Music, voices etc. An LED light
    will come on at dusk and go off at dawn, and 24/7 I want the sound of
    a muffled radio to be audible from inside the house.

    At present, I'm leaning towards a simple crystal set tuner with a half
    watt amplifier kit driving a large speaker?

    Any suggestions towards simplicity, cheapness, and above all, sound
    power to electrical power efficiency will be most helpful.

    Thanks, jack
     
  8. Genrally no.
    A piezo type would be fine for that.
     
  9. Won't fool the determined. Some alarm stickers on the doors and windows work
    better. A flickering blue light looks like a TV.



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  10. Guest

    Thanks Homer
    The determined will get in anywhere, but one must ask why they would
    be determined to break into a crappy old house amongst thousands of
    mansions.

    That's a great idea about the stickers, although it might advertise
    that you have got something to protect.

    The flickering blue light is pure genius. I wonder if there is a
    flickering LED array that could simulate a TV. That should be easy and
    cheap to incorporate. Thanks again, jack
     

  11. Stickers are useless, unless the stickers are from a local alarm
    company. Lots of places with those cheap, generic flea market stickers
    get hit. In fact, its an advertisement that the owner has something
    worth stealing, but is too damn cheap to buy real protection.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  12. It eliminates the smash in idiots. They prefer to try elsewhere. Another tip
    is to find the biggest dog dish you can, bash it up so it looks well chewed,
    and write Tiny on the side with a marker.
     
  13. Chris

    Chris Guest

    Hi, Jack. The power requirement for your radio is going to be
    determined by the volume of the speaker. Your radio circuit current
    apart from that will be much less. An older 9V transistor radio I
    built many moons ago had a current draw with the sound turned all the
    way down of 30mA or so. That would be around 250mW, much less than
    the power required to drive the speaker loud enough to hear outside.
    Thatw ill probably take a few watts, at least. With the efficiency of
    audio outputs in general, you can depend on several watts consumed to
    get two or three watts at the speaker. Even with a DC-to-DC
    converter, that will mean around a 1/2A current draw from your
    battery.

    Many small radios (particularly those that operate on 9VDC) have
    provision for an external car cigarette lighter adapter, allowing them
    to run directly off 12VDC. You also might want to look into this --
    it would be less hassle than a DC-to-DC converter, and you won't have
    to worry about electrical noise from the converter causing problems.

    I'd also recommend looking into a 12VDC marine battery, if you're
    buying one instead of scrounging it. They are made for deep
    discharge, and can put out the 1/4 to 1/2A you'll need (even with a DC-
    to-DC converter) for a longer time than an automotive battery.

    Good luck
    Chris
     
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