555 based continuity tester problem

Discussion in 'General Electronics Chat' started by Garurumon, Mar 12, 2014.

  1. Garurumon

    Thread Starter Member

    Mar 17, 2013
    99
    1
    Hi.

    I tried to build this continuity tester, and it looks nice, but it's sensitive like a woman on pms (screams like one too). It can even detect resistance from one of my legs to the other. Is that how it's supposed to work?

    Does anyone have an idea how to change it's sensibility so the sound deteriorates more with a greater resistances?

    Or maybe a different schematic that could fit my box, and has been proven working?

    The only difference that I made in the circuit was using a buzzer with a 47 Ohm resistor.

    EDIT: And yeah, funny thing is, the bigger the resistance the more it screams.
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Reduce sensitivity by resistor from +6 to base.

    If you have a buzzer then you don't need the rest of the circuit.:confused:
     
  3. Garurumon

    Thread Starter Member

    Mar 17, 2013
    99
    1
    Thanks, I'll try it now.

    And I don't get this part??
     
  4. BobTPH

    Active Member

    Jun 5, 2013
    782
    114
    The purpose of the '555 is to make a tone in the speaker. If you are using a buzzer, it is not needed. You could connect the transistor directly to the buzzer instead.

    Bob
     
  5. Garurumon

    Thread Starter Member

    Mar 17, 2013
    99
    1
    I thought you need to deform crystal at some frequency for it to vibrate/produce sound? :confused:

    I'm working with buzzer for the first time today... So, it will produce sound without oscillator?
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    I think you are confusing a "buzzer" with a speaker. Notice that the schematic calls for an 8Ω speaker, not a buzzer. In the case of a speaker, you do need an oscillator to produce the sound. In your photo, it is hard to tell whether you have a buzzer or a speaker. If it truly is a buzzer, all it needs is power to produce sound, whereas a speaker needs an oscillator.

    I suspect that you have used a buzzer, which is causing your problem.
     
  7. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Yes, a buzzer and a battery alone, makes a good low impedance continuity tester.
     
  8. Garurumon

    Thread Starter Member

    Mar 17, 2013
    99
    1
    yeah, but it won't change sound over wide range of resistances. Meh, I'll guess I'll find something good :/ Thanks all :)
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Your 555 circuit doesn't change tone either. It's just on or off.:confused:

    As long as you have it built, a 555 guru on here should be able to come up with one that changes tone with resistance.

    If not I could give it a try. I'm not a simulator though. :(
     
  10. Garurumon

    Thread Starter Member

    Mar 17, 2013
    99
    1
    what is a 555 guru? :O

    just tried putting it through my 555 based pwm, and switching it on and off at different speeds does look like it's changing sound. I'll try to make 555 VCO, maybe that'll work.
     
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