using an inductive amplifier to detect tones

Discussion in 'General Electronics Chat' started by fred_uk, Jan 3, 2009.

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  1. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    hi,

    im new to the forum and need some help with this project

    i have got

    > an audio cable with tones from 500hz to 3000hz present
    > an inductive amplifier, similar to this one http://www.maplin.co.uk/Module.aspx?ModuleNo=46536

    i want to detect the presence of a tone on the audio cable without making contact with the conductors, hence the inductive amplifier

    when i detect i tone between 500hz and 3000hz i want to activate an output for the duration of the tone, people have mentioned using the LM567 chip, but im told its osblete and i cant get the bandwidth required

    can anyone help me with either a modiciation to my exsiting tester or a complete circuit. Im upto the standard of buildind it but not designing it and need some help

    thanks
    fred
    [​IMG]
     
  2. duffy

    Active Member

    Dec 29, 2008
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    The LM567 isn't obsolete, you can buy them from Digikey. It will easily work to 3khz and quite a bit higher, I've used them to detect ultrasonics.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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  4. SgtWookie

    Expert

    Jul 17, 2007
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    National's LM567 is obsolete.
    The LM567C supercedes it:
    http://www.national.com/mpf/LM/LM567C.html

    However, the bandwidth is only adjustable from 0 to 14%. You'd need at least 15 of them to cover that frequency range.
     
    Last edited: Jan 3, 2009
  5. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    thanks beenthere, seems ideal, ive also downloaded abit of software on my pc and started testing tones with my current setup, ive found my inductive amplifier doesn't appear very sensitive but i think its got a filter on tones below 1000hz

    as i require to go down to 500hz im gona need to bin it and build my own, can anyone recommend an inductive amplifier circuit?

    all i will need to do then is put the audio output though the above circuit and i will be sorted.

    thanks again!

    woops...

    just noticed this comment...

    does that mean i will need 15 of these chips in the above circuit to cover the full frequency range??

    THANKS
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Do you want to see if some tone is present ?
    Just make a filter between 500 hz and 3000 hz, detect the envelope and see how high it gets.
    Do you want to see which tone is present ?
    You have to make more sharper filters (like in an equalizer) with the detectors.

    Greetings,
    Bertus
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
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    I think he wants "to detect any tone presence within the 500 ~ 3000Hz range and light a LED".
     
  8. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    thats what i want to do....

    my exsiting inductive amplifier from maplins isnt really made for what i want to achieve and is only good at >1000hz
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Last edited: Jan 4, 2009
  10. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    ar!

    im not too sure how strong these signals are, ive got a program on my pc for generating the tones so i can test the system out

    i've not got a coil, instead i had used an inductive amplifier (like a cable tester type thing)

    ive seen that circuit before, ideally all i need is somethin like this that could provide an output (would need to support a 100ma load) im abit concerned that i would get too much interferance from mains humm and that, thats my reason for wanting to filter out anything below say 400 to 500 hz, how could i do that?

    thanks everyone, out of all the forums ive tried you guys are coming up with all the answers! thanks again

    fred
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You can change the responce of the circuit I linked to.

    [​IMG]

    If you make the entrance capacitor ( now 100n ) smaller the circuit will be less sensitive for lower frequencies (low cut).
    If you make the capacitor across the opamp ( now 150p ) higher the circuit will be lees sensetive for the very high frequencies (high cut).

    Greetings,
    Bertus
     
  12. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    thanks will get to work contructing this circuit tomorrow, what do i do about the output? i've got two options for my output device, they are:

    option 1 80ma 1.0 - 1.8v
    option 2 100ma 2.4 - 3.6v

    both small dc motors

    i presume extending or shortening the lenght of cable on the probe would affect the units 'range', do i make that as a coil??

    thanks for your prompt replys!
     
  13. bertus

    Administrator

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  14. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    tiny dc motor
     
  15. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You could make a comparator, connect one side to the "meter" and the other side to a potentiometer to set the level.
    The output of the comparator can drive a transistor to switch things.
    (you need to reduce the voltage for the motors).

    Greetings,
    Bertus
     
  16. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    thanks for that,

    can i remove the metre from the circuit??

    thanks
    fred
     
  17. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Yes, you can replace it by a 1k resistor.
    This is to let the 220 uF capacitor to let the voltage go, when there is no signal.

    Greetings,
    Bertus
     
  18. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    thankyou for your assistance, im goin to get the bits tomorrow, where would i take the output for the motor?

    thanks bertus
     
  19. italo

    New Member

    Nov 20, 2005
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    I think his question was how to detect not where to find decoders. Maybe i am wrong? audio cable to me means shielded cables. if that is so then nothing will be able to magnetize a shield because is sitting at virtual gnd. So just throw that idea away. And the pictcure shows telephone circuitry detection. send a tone to a wire then probe to find the wire usefull for telephone continuity check they have no shield just millions of wires laying around.
     
  20. fred_uk

    Thread Starter Active Member

    Jan 3, 2009
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    the cable isnt shielded
     
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