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I need your help

obelloobello Posts: 3
edited 2009-03-30 17:47 in Accessories
Hello, I am working in a project where I need to check the presence a buzzer; the buzzer works with a spectrum audible. I think, I can do it with a microphone, for example, when the buzzer is ringing the microphone recives the sound, of course, I will need to prepare the signal, but I have a·hypothesis, how the spectrum is audible, my·circuit·can be in fault with some sound its recive, isn't it?

How do you think????? I hope you understand me, because my English is bad.

Regards . . .

····

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-03-26 04:54
    Here is one example: www.uashem.com/images/security/soundsw.gif. You can find similar examples with an internet search. This circuit operates on 12V. I would use two 1N4148 diodes in series with LED1 like this: (Ground -- LED1 -- 1N4148 -- 1N4148 -- 2.2K resistor). I would connect the Stamp I/O pin to the junction of the 1N4148 diode and the 2.2K resistor. That would provide an "on" voltage of about 3.1V (and an "off" voltage of 0V). This is well above the threshold for the Stamp I/O pin, yet not anywhere near the maximum I/O pin voltage of 5V.

    R1 is used to provide an operating voltage if you're using an electet microphone that requires it.

    Pretty much any general purpose NPN transistor can be used for the BC109C and pretty much any general purpose PNP transistor can be used for the BC212B. The diodes can all be any general purpose switching diode like the 1N4148 or 1N914. You can leave out the relay (RL1) and its protective diode.

    Post Edited (Mike Green) : 3/26/2009 5:03:07 AM GMT
  • obelloobello Posts: 3
    edited 2009-03-27 20:47
    Thanks Mike, but I tink if I put a receptor, I will have problems, because my buzzer works in a frequency audible, it is 666.66 Hz. And my receptor·can be wrong, beacuse my recepetor can give me out signal, though the frquency·is not precisely that of the·buzzer.

    What is your opinion?
  • Mike GreenMike Green Posts: 23,101
    edited 2009-03-27 21:03
    Yes, the detector I showed you is relatively insensitive to the frequency of the sound. You didn't say you wanted frequency discrimination. It's possible to add a filter to the circuit, probably between the 2nd BC109C transistor and the BC182B transistor. Do an internet search for "active filter design". You want a simple narrow-band bandpass filter to allow through only those frequencies near to the buzzer's frequency. One example I found was www-k.ext.ti.com/SRVS/Data/ti/KnowledgeBases/analog/document/faqs/ssttbphq.htm. The website (en.wikipedia.org/wiki/Active_filter) is quite thorough (single supply active filter design).
  • LeonLeon Posts: 7,620
    edited 2009-03-30 14:10
    Why not use a suitable MCU and do the detection in software? Or, use a PLL like the 74HC4046?

    Leon

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  • obelloobello Posts: 3
    edited 2009-03-30 17:47
    Yes, I was thinking, and my conclusion is that I'll make the device, and converter frequency to voltage, with MCU here I'll read a signal input in the buzzer, and sound it I'll check with a microphone, how said me Mike.

    Thanks and advance
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