automatic doorbell

Discussion in 'General Electronics Chat' started by rijoe.mathew, Sep 21, 2014.

  1. rijoe.mathew

    Thread Starter Member

    Sep 21, 2014
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    i have this circuit for my project.can i replace the 7555 with ne 555.what are the changes needed.please reply fast.

    anyone please reply fast.i need this for tomorrow
     
    Last edited by a moderator: Sep 21, 2014
  2. crutschow

    Expert

    Mar 14, 2008
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    The 7555 is a CMOS version of the original 555 which uses BJT transistors. It should work in your circuit.

    Note that there appears to be an error in that circuit. I think there should be a dot where the pin 6 connection crosses the pin 2 connection to indicated they should be connected together. Also, that circuit is not the typical astable multivibrator circuit for a 555 as seen here.
     
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  3. ericgibbs

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  4. rijoe.mathew

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    Sep 21, 2014
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    [​IMG] now i replaced the original circuit 7555 with this circuit where R1=600 ohms,R2=18 kilo ohms, and C=.001uF.Is there any problem with the connections of LM324.Please advise how to identify the emitter of BC337 and BC327.its seems like the two transistor are heating up when i connect the input.please advice.is the any polarity for ultrasonic transducers
     
  5. ian field

    Distinguished Member

    Oct 27, 2012
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    You may find lower resistances are needed around the timing pins.

    An undesirable feature of the bipolar 555, is the crossover point on the output stage - it has a tiny blip of crowbarring Vcc as one transistor hands over to the other, this can glitch other parts of the circuit.

    You should put a 100nF cap as close as possible to the 555 supply pins, you should also have some bulk reservoir/bypass of at least 100uF for the whole circuit.
     
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  6. ericgibbs

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    hi rijoe,
    You cannot use that version of a 555 astable to drive an ultrasonic transducer.
    It requires a 50:50 drive signal, at the same frequency as the original design. You will 'cook' the drive transistors!

    Why have you changed the 555 circuit,?

    Eric
     
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  7. rijoe.mathew

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    Sep 21, 2014
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    when i used the circuit given in the diagram.it didnt work.i was not getting a 40khz signal at the output when i connected it to a CRO
     
  8. rijoe.mathew

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    Sep 21, 2014
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    Is there any mistakes in amplifier part.it seems like some dots(connections) are missing
     
  9. ericgibbs

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    hi,
    Its runs OK in LTSpice sim, attached.
    There is an error on the LM324 wiring.

    I would say pin5 and pin 1 should be linked, not pin 5 and pin 2.?
    E
     
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  10. rijoe.mathew

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    Sep 21, 2014
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    what is the value of C2 in this circuit
     
  11. ericgibbs

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    A 10nF will be OK.
     
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  12. rijoe.mathew

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    Sep 21, 2014
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    can i use .001uF or 10uF
     
  13. ericgibbs

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    Use 1nF [ 0.001uF] its OK.
    E
    Make sure you have the BC transistor pins correctly identified.
     
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  14. rijoe.mathew

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    Sep 21, 2014
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    can I replace the BC 337 and BC 327 with SK100 and SN100
     
  15. ericgibbs

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    hi rijoe,
    Could you please post a link to the site where the circuit design was posted.?
    The amplifier circuit as drawn will not work correctly.

    E
     
  16. Bernard

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    Aug 7, 2008
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    Looks like there will be lots of shoot thru, ie , both transistors conducting at the same time = heat. Might consider connecting as emitter followers??
     
  17. ian field

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    Oct 27, 2012
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    Are you saying you can't get 50:50 from a bipolar 555?!

    With a couple of steering diodes and a pot you can adjust the duty cycle from about 5% to about 95%.

    The best way to get accurate 50:50 is ignore pin 7 and take the timing resistor from pin 3 - this also saves the current limiting resistor from pin 7 to Vcc.
     
  18. ericgibbs

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    No, I did not say that.
    I said a version where the Output is connected to the timing components will give a 50:50 pulse period, of course pin3 is used as the output.
    Why add diodes etc, when a simple solution already exists.?
    Which will not give an exact 50:50 period anyway.

    The circuit the OP is using is driving a resonant ultrasonic transducer, so a closer 50:50 will give a better result.

    E
     
  19. rijoe.mathew

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    Sep 21, 2014
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  20. ericgibbs

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    hi,
    I have posted a comment on his web site asking him if has actually built and tested this circuit, as it will not work as drawn.
    If I get a response I will let you know.

    E
     
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