WHo can tell me what is wrong with this circuit?

Discussion in 'The Projects Forum' started by doug08, Oct 25, 2011.

  1. doug08

    Thread Starter Member

    Jan 30, 2011
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  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    I would think that putting a tank coil straight to ground from the 555 output would cause far too much DC output current flow. The tank filtering will also be pretty much of an illusion driven from a totem-pole output.

    http://www.national.com/ds/LM/LM555.pdf

    There are others about with particular interest in 555 circuits who may comment, but I don't think this arrangement is any good.
     
  3. doug08

    Thread Starter Member

    Jan 30, 2011
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    It was the only thing I could see that would cause it to heat up so bad. I guess just lower the input voltage.... I used a 1000uh coil/200 pf cap.
     
  4. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Perhaps a photo of the circuit you built??
     
  5. Adjuster

    Well-Known Member

    Dec 26, 2010
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    A DC blocking cap and a series resistor in the line to the tuned circuit would be more to the point, so that the poor old 555 gets a manageable load.

    That said, this thing may be illegal anyhow. What frequency are you trying to send? (356kHz???)
     
  6. chrisw1990

    Active Member

    Oct 22, 2011
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    your pin 5 isnt conncted..
    pin 5 should is frequently connected through a 0.01uf(10nF) cap.
    the potentiometer isnt going to be doing much with the wiper and one end connected to supplyV
     
  7. doug08

    Thread Starter Member

    Jan 30, 2011
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    This is a 2 part circuit. This is the transmitter portion. I made the 1000uh inductor coil, and used a 200pf cap. The receiver portion will have the same 1000uh coil, with a 75-250pf trimmer. I used a 9V battery snap, but tried the specified 12v supply....Hot as hell with seconds.

    [​IMG][​IMG]
     
  8. doug08

    Thread Starter Member

    Jan 30, 2011
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    Yes, comes out to 356 khz. This is a locating device. The other part of the circuit has 5 led's that will illuminate as you near the transmitter.
     
  9. chrisw1990

    Active Member

    Oct 22, 2011
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    i get the feeling your following a design..?
     
  10. doug08

    Thread Starter Member

    Jan 30, 2011
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    Just saw the circuit online and decided to make it.
     
  11. chrisw1990

    Active Member

    Oct 22, 2011
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    can you provide a link?
     
  12. doug08

    Thread Starter Member

    Jan 30, 2011
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  13. chrisw1990

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    Oct 22, 2011
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  14. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    I wonder if anybody ever built this and it was working? :rolleyes:

    The 555 frequency is adjustable from 1.17kHz upwards. Then the LC at the output could be anything between 187kHz and 1.6MHz. :confused:
    Every time the 555 output switches (with it's much lower output frequency) it would cause an oscillation in the LC which would immediatly cease IMO because the output will be either tied to + or GND. The rest of the time current will flow through the inductance when the 555 output is HIGH, causing it to heat up...
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    Lowering the input voltage voltage will not help, the coil is a dead short. A 555 connects directly to ground, and couples to Vcc pretty tightly when it is switched that direction. You can isolate pin 3 via capacitor, or find some other way to do it. I assume you are trying to filter out a sine wave? A 3 stage low pass RC filter might do much better.

    You could move C3 to pin 3.

    I've seen a lot of circuits trying to use the 555 for an AM circuit. A 555 is basically a digital chip, this does not work very well I'm afraid. You would produce more power, use fewer components and produce a much cleaner signal with a simple transistor oscillator. The 555 is about as unsuitable for this as anything I've ever seen.
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    The transmitter is a very poor design.

    The receiver is also a joke. Its lousy old 741 opamp has trouble above 9kHz and here it is trying to amplify 356kHz. It should be a high frequewncy opamp with a high slew rate.
    The tuned circuit is shorted by the very low 1k ohm input impedance of the inverting opamp circuit. It should be a non-inverting opamp then it can have a high input impedance so the tuned circuit is not loaded down and can have good selectivity.

    Why do the LEDs have parallel resistors?
    With the plus and minus 9V supply, the output of the 741 opamp will not go high enough to light 5 LEDs in series.
     
  17. badrobot

    New Member

    Jan 1, 2011
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    have You tryed a fast sw diodes serial on 555 output?
     
  18. abdul qayyum

    New Member

    Nov 3, 2011
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    in such circumstances you must follow these steps:
    1. check that the hot ic is working of the circuit or is burned (you can check using tester)
    2. if ic is working then find all currents to and from the ic and compare it with specification if it is correct then come the then
    3.you must recognize that you are using inductor in your circuit so two problems might be there:
    1 peak inverse voltages are damaging the circuit or
    2 there is a problem of interfacing you must draw block diagram of the circuit and determine the ports in between the blocks now determine the currents and power transmission i am sure that the problem lies in interfacing so you must add circuits or components require to compensate the effect.
     
  19. sheldons

    Well-Known Member

    Oct 26, 2011
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    isolate pin 3 ,switch on and see if yr 555 gets hot.....decouple pin 5 to pin 1 with a 0.1 mf cap....also disconnect one end of yr preset(the end to pin 7...)and insert a 1k resistor there let me know if you have a working osc. with no heating 555
     
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