3kHz Tone Detector Circuit

Discussion in 'The Projects Forum' started by Teg Veece, Jan 8, 2007.

  1. Teg Veece

    Thread Starter Member

    Mar 14, 2005
    As part of a robot project, I'm trying to develop a sound activation system so that the robot will start up upon detecting a 3kHz tone.

    I have a good idea of the kind of circuit I want to build (a microphone followed by an amplifier and a LM567 tone detector IC) but I'm not too sure where to order the parts from (its my first time ordering my own parts).
    I found a suitable buzzer and microphone on radioshack
    but I'm living in Ireland and radioshack only delivers in the U.S.
    I found a buzzer on Maplins http://www.maplin.co.uk/Module.aspx?ModuleNo=3221&doy=search but I'm not too sure about the microphone.
    What kind of a microphone would be best suited to this circuit? The original one which I was advised to get from radioshack is a electret one. Does anyone know where I can find a site that will deliver this kind of a mic to Ireland? Preferrably off the same Maplin site. I have found a few possible candidates but I'm not too sure how essential the type of mic is to the overall design. Any help or advise offered would be greatly appreciated.
  2. Teg Veece

    Thread Starter Member

    Mar 14, 2005
    I found this microphone off Farnell, http://ie.farnell.com/jsp/endecaSearch/partDetail.jsp?sku=1299766 except I'm not too sure if its a suitable alternative to the one recommended by the schematic I acquired for my 3 kHz tone detector. (I've attached the schematic but its also found here http://members.cox.net/rbirac3/Snuffy/tone_detect.htm)

    The mic that the diagram recommends has 3 leads, but the one I found on Farnell only has 2. How do I go about integrating this new mic into the circuit? From looking at the mic in the schematic, it seems to require a 5dc VCC and a ground, then it outputs its signal on the 3rd line. But the mic on Farnell doesn't seem to have a VCC line which is where the confusion is arising.

    Help needed on this one.
  3. hgmjr


    Jan 28, 2005
    The microphone you have located is of the electret type as far as I can tell. Follow this link http://en.wikipedia.org/wiki/Electret_microphone to the wikipedia website where there is some information on electret type microphones.

    You can also google electret micrphones and find some example circuits that can provide you with ideas on how to use it in place of the 3-terminal mike called for by the circuit example.

    I don't know if you are aware of it or not but the NE567 is only going to give you a tone-present signal as long as the 3KHz tone persists. If you need the output of the NE567 to remain active once the 3KHz tone is off, you will need to provide a latching circuit at the output that toggles with each burst of the 3KHz tone.

  4. Teg Veece

    Thread Starter Member

    Mar 14, 2005
    Yeah, thanks for that.
    The output will be going into the IO pin of a microcontroller so there won't be any need to latch it.
    In the end I just used a spare buzzer that I ordered to act as a microphone using the reverse piezoelectric effect. Works like a charm too.
    Thanks again for the help.