Keys finder circuit

[lapsap]

after testing the circuit part by part, the circuit oscillation part finally working (i think so).

but when i connect it to the battry,  the piezo start buzzing, after few second it stop. and then start buzzing again. when i short the base of T1, the sound will non stop buzzing.

R5 C3 N4 is the filter circuit? whats the name of this part?

Quote:
The integral circuit

sound.rar

 

[audioguru2]

but when i connect it to the battry,

 

[lapsap]

mp3 is just a audio file, any media player will be able to play it.
just in case here is the zip format, because this forum does not allow to attach mp3 files, i ll need to zip it up.

now the problem i m facing is that, when i connect the circuit to the battery, the piezo will start buzzing for non stop, even there is no any sound in the environment except the piezo buzzing.

when i remove the C1, the circuit will stop buzzing after a short buzzing. does that work as when there is no sound from the mic?
but when the C1 remain there, i just disconnect the connection between C1 and R10, it will be same as the previous case, buzzing, stop, buzzing, stop...

why do we need a C1 over there?

sound.zip

 

[audioguru2]

mp3 is just a audio file, any media player will be able to play it.
just in case here is the zip format, because this forum does not allow to attach mp3 files, i ll need to zip it up.

Hi Lapsap,
Thanks for the zipped intermittent beep.

now the problem i m facing is that, when i connect the circuit to the battery, the piezo will start buzzing for non stop, even there is no any sound in the environment except the piezo buzzing.

It should stop buzzing a couple seconds after connecting the battery, if the room is quiet.

when i remove the C1, the circuit will stop buzzing after a short buzzing. does that work as when there is no sound from the mic?

Yes.

but when the C1 remain there, i just disconnect the connection between C1 and R10, it will be same as the previous case, buzzing, stop, buzzing, stop...

Then that is the key to your problem. D4 is shorted or backwards, or C7 is open.
D4 is supposed to rectify the oscillator's output, charge C7 and feed the positive voltage through D3 and R1 to the input of N1. Then N1 is disabled and shouldn't pass the oscillator's signal through N2 and N3. Without an output from N3, then D1 won't pass positive peaks to the input of N4 so its output remains at half of the supply voltage and causes T1 to turn on which stops the oscillator.

why do we need a C1 over there?

C1 passes the piezo's signal as a microphone to the input of N1. It also blocks the DC ground voltage from R10.

With the project buzzing when it shouldn't, measure the DC voltage at the output pin 8 of N4. Also measure the DC voltage at the output pin 6 of N3.
What is your supply voltage? ;D

 

[lapsap]

i m using a 12V battery to test it, but when i using a 12v power supply it works fine. the only thing is that the mic cant pick up signal.

can i put a mic parallel with the piezo, so that it can receive the whistle or some other signal.

btw way, can i increase the gain of the amplifier? (N1...N3) what is this call? do you have any document for this amplifier so that i can refer?

 

[audioguru2]

i m using a 12V battery to test it, but when i using a 12v power supply it works fine, the only thing is that the mic cant pick up signal.

If it works fine with a power supply then its mic picks up a signal, right? Then what is wrong with your battery? Maybe it can't supply enough current.

can i put a mic parallel with the piezo, so that it can receive the whistle or some other signal?

Not without re-designing the circuit for a separate mic.

can i increase the gain of the amplifier? (N1...N3) what is this call? do you have any document for this amplifier so that i can refer?

It is a high gain inverting amplifier, its gain is determined by the ratio of R2/R1 and the value of C8.
It should work fine as shown. Maybe your piezo is incorrectly mounted which would damp its sensitivity, or maybe it isn't mounted in a suitable resonant chamber. Maybe it is too small.
Did you replace IC1?
Did you measure the DC voltage at the output of its preamp on pin 6?
Did you see the output of its preamp with an oscilloscope?
How did you fix it so that it doesn't continuously beep?

 

[lapsap]

after i change the 12V with a 9V battery, it works fine, it also can receive signal. but it seem like only whistle will not be able to trigger the circuit, i will need sound that louder.

when i test wif power supply again, reduce the current, it seem like continuous beeping again, why?


i did not change the IC1 to stop the continuous beeping sound.

 

[audioguru2]

after i change the 12V with a 9V battery, it works fine, it also can receive signal. but it seem like only whistle will not be able to trigger the circuit, i will need sound that louder.

Hi Lapsap,
Good, it works. ;D
I tested a 30mm diameter piezo transducer just now from a cheap alarm clock. The piezo has a small resonant chamber in front of it with a 3mm hole for the sound. As a speaker, it is poor until about 4kHz when it whistles very loudly. As a microphone, it is also poor until about 4kHz, when it is very sensitive. I can't whistle above about 2.8kHz so it is not sensitive to my whistle.
The circuit is designed to respond to a fizzle, isn't it?

when i test wif power supply again, reduce the current, it seem like continuous beeping again, why?

Maybe your power supply is not regulated or has poor filtering and produces mains ripple. Then the AC ripple voltage passes through R3, D2 and D1 causing the input of N4 to be a little high, and therefore its output to be low. Then T1 is turned off and the oscillator is allowed to run.
You didn't post measured voltages so I am just guessing. ;D

 

[lapsap]

buy why when using a 9V battery will work instead of 12V battery? 12V battery low current?


oh ya, mayi have your name? i m doing this as a project, can i put your name in my report?

 

[audioguru2]

but why when using a 9V battery will work instead of 12V battery? 12V battery low current?

If your 12V battery cannot supply enough current then its voltage would drop far below 12V.
Maybe N4 doesn't self-bias itself at half the supply voltage. If its self-bias voltage is 1.2V lower than half-supply, then it will have its input voltage too high from D1. Then its output voltage would be low, turning off T1 and allowing the oscillator to run. Reduce the value of R4 or increase the value of R3 to fix it.

oh ya, may i have your name? i m doing this as a project, can i put your name in my report?

He, he. I don't have a name. Just call me "Audioguru". ;D

Did you try putting your piezo in a resonant chamber so that its whistle output is very loud and it is very sensitive as a 4kHz microphone?
Did you find something to make a 4kHz fizzle sound to activate this project?

 

[Alun]

Try using a bigger piezo transducer as it will have a lower resonant frequency.

About the name thing, fair enough  audioguru for not wanting to reveal your real name over the Internet you're quitte shy aren't you? ;D There again you just don't know we might have an axe murderer here who will kill you if the the highly unlikely event you mistakenly give them some bad advice on a circuit. ;D I'm not scared though so I use my real name if someone wanted to find me I'm sure they could track my IP address and find out where I live and if they wanted to kill me I don't think they'll care what my name is. ;D

lapsap, (if that is your real name  ;D)
Why don't you mention this site and perhapps the name of the autor, hang on a second, does anyone know the author of this project, did audioguru design it? You could still mention audioguru anyway as he did help you and most importantly the name of this site.

 

[audioguru2]

Hi Alun,
The project's author is unknown, like me. ;D
I keep my name a secret because sometimes I reveal bad things about my previous employers and manufacturers. I talked about the big skunk under my porch and I don't want more to find out where I live. It dug another hole under there again last week. ;D

I would never design such a lousy circuit. I would use a real microphone and a real opamp for it. I might even include voice-recognition or a counter into it in case you have more than one of these "finder" circuits.

I can find my wireless home phone by pressing a button on the base-station and causing it to ring. I wish my TV remote had one when I misplaced it last night. :

 

[lapsap]

hello,

when i made a whistle the circuit cant be trigger, but then i knock on the table it start buzzing n when i made a loud sound. does that means the piezo i get is not good? becoz when i say piezo tranducer the shop keeper say no idea, so i get the piezo that without oscillator.

after that i made a PCB, but now it cant be trigger even when i manually use the function generator to give signal.

when i tested on the project board, when i knock the table, short circuit of T1's base n emitter or give signal by funtion gen for least then a second, it is trigger then buzzing for a short period of time then it stop.

but after the PCB is done it only trigger when is short circuit of T1's base n emitter
after remove the wire, it will instantly stop (what does this mean?)

as for the name thing, thx for the suggest, Alun, it ok for me to mention this site and the name "audioguru", audioguru?

 

[audioguru2]

when i made a whistle the circuit cant be trigger, but then i knock on the table it start buzzing n when i made a loud sound. does that means the piezo i get is not good?

Hi Lapsap,
Like I said before, the circuit is designed to respond to a fizzle sound, not a whistle sound. I can't make a whistle sound anywhere near as high as the 4kHz resonant frequency of my piezo transducer. I don't know what is a fizzle sound, but it needs to be at the resonant frequency of the piezo.

after that i made a PCB, but now it cant be trigger even when i manually use the function generator to give signal.

when i tested on the project board, when i knock the table, short circuit of T1's base n emitter or give signal by funtion gen for least then a second, it is trigger then buzzing for a short period of time then it stop.

Then there must be something wrong with your pcb.

but after the PCB is done it only trigger when is short circuit of T1's base n emitter
after remove the wire, it will instantly stop (what does this mean?)

After releasing the short of T1's base-emitter, C4 should take a short period of time to charge then T1 can turn-off the oscillator. Since now it happens instantly, then C4 is open and/or R6 is shorted.

as for the name thing, thx for the suggest, Alun, it ok for me to mention this site and the name "audioguru", audioguru?

Sure, you can mention Electronics-Lab and Audioguru. ;D

 

[lapsap]

after changing the IC, now it is working. but for some reason i will need to use my hand and touch the circuit then only is working. if i didn't do that, when the circuit is trigger, it will buzzing, stop, buzzing, as i mention it before.

some have i mannage to use my whislte to trigger the circuit.

thx, audioguru and others help me out.

 

[audioguru2]

Horray! ;D

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