555 based continuity tester problem

Thread Starter

Garurumon

Joined Mar 17, 2013
99
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.
 

inwo

Joined Nov 7, 2013
2,419
Reduce sensitivity by resistor from +6 to base.

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

BobTPH

Joined Jun 5, 2013
2,576
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
 

Thread Starter

Garurumon

Joined Mar 17, 2013
99
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
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?
 

tracecom

Joined Apr 16, 2010
3,944
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.
 

inwo

Joined Nov 7, 2013
2,419
yeah, but it won't change sound over wide range of resistances. Meh, I'll guess I'll find something good :/ Thanks all :)
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. :(
 

Thread Starter

Garurumon

Joined Mar 17, 2013
99
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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