Electronic keys finder

DerStrom8

Super Moderator
Hey everyone!
I'm fairly new here, so please bear with me

I just built this circuit (link shown below) for an electronic keys finder. It's designed to respond to a "fizzle" according to the site. However, when I turned on the power to my breadboard, the buzzer started it's long "answer" tone, which soon faded out (like it was supposed to), but then it started back up again without me making a sound. It continues to do this unless I turn off the power. I was just wondering if anyone could tell me what might make it do that. Could it be that the N4 inverter is damaged and the circuit responds to ordinary noise? Or maybe an extra surge of power resets it and causes it to restart?
The circuit can be found at
http://www.diy-electronic-projects.com/p104-Keys-Finder
I would greatly appreciate any help that you guys can give me!
Thanks in advance!
-Der Strom
 
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The project was removed from Electronic-Lab because it does not work.
I think it was poorly translated from Greek to Engrish so it says, "fizzle" instead of whistle.

It uses a piezo transducer not a piezo buzzer (another translation error). A piezo buzzer (with a built-in oscillator) would probably keep buzzing by the DC from the transistor driver.
A piezo transducer is both a microphone and a speaker.

The problem is that the piezo transducer is very sensitive at its 4kHz resonant frequency and nobody can whistle higher than about 2kHz.
The project beeps when it hears a 4kHz smoke detector. Try it.

My daughter bought a cheap keys-finder at The Dollar Store. She wanted me to fix it because it beeped whenever the TV was on and whenever she talked. I couldn't make it beep and I couldn't fix it.
 

Thanks a lot for the quick reply!
I figured that the translation was a little off, so I used a piezo TRANSDUCER instead of the buzzer, and I tried whistling, "pssst"ing, and any other noises that might trigger it. I didn't even think about its resonant frequency. That explains a lot. When it kept making it's noise, I had it hooked up with and astable 555 circuit to get the tone.
Thanks again!
Der Strom
 
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So, since the previous circuit doesn't work correctly, I am looking for another one that responds to a whistle. I've found one other one so far that is based on a CMOS 4049 hex inverter, but the 4049 that I pulled off an old circuit board is broken. Are there any other circuits (or even chips that would work as well as the 4049) out there that I can try? Thanks!
-Der Strom
 
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The CD4069 has a perfectly symmetrical output so it makes a pretty good amplifier. It draws low supply current.
A CD4049 has a lop-sided output. Its output sinks (going low) much more current than it sources (going high) so it is biased wrong when used as an amplifier. It draws high supply current.

Please post the schematic of the new circuit so we can see any other problems it has.
 

Right. So here's the schematic of the new circuit that I hope to try:
**broken link removed**
Thanks!

Oh, and the part values are as follows:

R1 22K 1/4W Resistor
R2 10K 1/4W Resistor
R3 4M7 1/4W Resistor
R4,R8 100K 1/4W Resistors
R5 220R 1/4W Resistor
R6 330K 1/4W Resistor
R7 47K 1/4W Resistor
R9 2M2 1/4W Resistor
R10 1M5 1/4W Resistor
C1,C5 47nF 63V Polyester or Ceramic Capacitors
C2,C3 10nF 63V Polyester Capacitors
C4,C6 1µF 63V Electrolytic Capacitors
D1,D2 1N4148 75V 150mA Diodes
IC1 4049 Hex Inverter IC
Q1 BC337 45V 800mA NPN Transistor
MIC1 Miniature electret microphone
BZ1 Piezo sounder (incorporating 3KHz oscillator)
B1 2.8 or 3V Battery
 
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I have also seen that circuit somewhere. It will probably work but will work much better with a CD4069 IC (but its pin numbers are different to a CD4049) and a couple of resistor values must be tweaked.
 
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