Astable multivibrator 555 problem in circuit

Discussion in 'Homework Help' started by faria_syd, Aug 29, 2015.

  1. faria_syd

    Thread Starter New Member

    Aug 29, 2015
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    http://www.electronicshub.org/super-sensitive-intruder-alarm/
    Hey i am a 3rd year engg student doing this project. The sensor part is working but alarm is not ringing.. I am using an 8ohms speaker and R4 n R5 as 1k. Please suggest changes that would make it work and should i use a buzzer instead of speaker. please give complete details as i am not very well versed with 555 working
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi Faria,
    Have you calculated the frequency of the Astable with 1K's for R4&5 with a 0.01uF cap.??
    E
     
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  3. faria_syd

    Thread Starter New Member

    Aug 29, 2015
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    48khz is the frequency. Should that be altered?
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    Hi,
    You will not hear 48kHz, design for for around 3kHz, this a frequency we can hear OK.
    Try R4 and R5 at 10K, that should be around 5kHz, lets know how it goes.

    E
    EDIT:
    If you want close to 3kHz, use 15k's
     
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  5. faria_syd

    Thread Starter New Member

    Aug 29, 2015
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    Is a coupling capacitor of 10uf before speaker okay or i need to use some other value
     
  6. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi f,
    For a simple 'sounder' a 10uF thru 100uF should be OK.
    Let me know when it works.
    E
     
  7. faria_syd

    Thread Starter New Member

    Aug 29, 2015
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    I used R1as 56k n R2 as 10k with C 0.01u
    It works extremely well now. Thanks Eric
     
  8. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    That is approx 3.2kHz.:)
    I have found that a frequency around 3kHz is quite a penetrating tone.
    E
     
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  9. faria_syd

    Thread Starter New Member

    Aug 29, 2015
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    Thanks once again.. Now i can b assured of great grades coz of ur help
     
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