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Thread: Comment on this Circuit

  1. 14th January 2006 10:59 AM #1
    akg
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    Hi all..
    some threads below . 'audio' has posted a ckt of RF Tx using logic chips
    now i think this ckt is really ingenious in the design.. using chip that is never intended to use like that...
    what do u think ? ....
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  2. 14th January 2006 11:48 AM #2
    audioguru
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    I don't think a crystal mic has enough current to force the input of an LsTTL gate low.
    I don't think a Schmitt trigger inverter will oscillate with its input directly connected to its output.
    Maybe miracles happen.
    Uncle $crooge
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  3. 14th January 2006 01:46 PM #3
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    Quote Originally Posted by audioguru
    I don't think a crystal mic has enough current to force the input of an LsTTL gate low.
    I don't think a Schmitt trigger inverter will oscillate with its input directly connected to its output.
    Maybe miracles happen.
    i was also confused by the usage of schmitt triggered ttl , but his website says "it works" .. :roll: ... hmmm..
    visit http://www.uoguelph.ca/~antoon/circ/uspy3.htm
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  4. 14th January 2006 03:35 PM #4
    audioguru
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    Quote Originally Posted by akg
    his website says "it works" .. :roll: ... hmmm..
    Watch out for circuits on the web. Maybe his wire from the output of the Schmitt trigger inverter to the input had resistance. Then it would oscillate.

    I spotted one of his FM transmitters with its preamp transistor incorrectly biased. Maybe he connected it with its collector and emitter wires reversed by mistake, then the transistor's current gain would be low and the transistor would work.
    Uncle $crooge
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  5. 14th January 2006 05:32 PM #5
    Roff
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    I'm betting it works.
    Anybody have a 74LS13? 74LS132?
    Ron

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  6. 14th January 2006 05:59 PM #6
    audioguru
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    I guess the output of a 74LS13 must have some output resistance that would allow it to oscillate. Right?
    Uncle $crooge
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  7. 14th January 2006 09:26 PM #7
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    Quote Originally Posted by audioguru
    I guess the output of a 74LS13 must have some output resistance that would allow it to oscillate. Right?
    And propagation delay. Note the tuning capacitor on the output which uses the output resistance to create variable delay, and hence variable frequency.
    Ron

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  8. 15th January 2006 10:34 AM #8
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    Quote Originally Posted by audioguru
    Maybe miracles happen.
    as far as i know.. electronics is a science.. so is there any chance for miracles ?? if it works then there should be some reason .. the best thing would be to test it..does any one has the ic , and a 5min to spare?? . (i have time but no ic :wink: )
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  9. 15th January 2006 11:41 AM #9
    eblc1388
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    Quote Originally Posted by akg
    as far as i know.. electronics is a science.. so is there any chance for miracles ??
    Certainly, according to Mr. M.... :shock:
    L.Chung
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  10. 15th January 2006 01:13 PM #10
    Nigel Goodwin
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    Quote Originally Posted by eblc1388
    Quote Originally Posted by akg
    as far as i know.. electronics is a science.. so is there any chance for miracles ??
    Certainly, according to Mr. M.... :shock:
    A miracle is simply something you don't understand YET! - so there's certainly scope for them in electronics.

    As regards the circuit above, the chances of it working depend entirely on what's inside the 'little plastic box with legs on' - it's entirely possible that some makes of 74LS13 may work? - but using a logic chip in this kind of way is completely dependent on how it's constructed, and different manufacturers will make them differently.

    But it's such a crap circuit anyway!, even if it worked it's only a novelty.
    PIC programmer software, and PIC Tutorials at:
    http://www.winpicprog.co.uk
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  11. 16th January 2006 05:22 AM #11
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    Quote Originally Posted by Nigel Goodwin
    A miracle is simply something you don't understand YET! - so there's certainly scope for them in electronics.
    hmm...... :roll: ....u r a veteran so no arguments...
    i'll have a check ... :?
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