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Mic detection circuit

Discussion in 'General Electronics Discussion' started by rer, Jul 31, 2015.

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  1. rer

    rer

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    Jul 31, 2015
    Hello everyone.

    I'm trying to create a circuit that would detect if a microphone is turned off or on. I want to plug it into my device then flip the switch and see an LED light up on my circuit. As simple as it sounds, I can't get enough current or any type of signal from a mic's jack.


    I'm using a similar mic with a cord.

    [​IMG]
    The jack is similar to.

    [​IMG]
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    You say "similar" your photo indicates a "Dynamic" mic. To me this means a coil and diaphragm as apposed to an Electret mic. I googled the mic in your photo. Does yours have similar specs.
    M-5 Dynamic Mic

    Chris
     
  3. rer

    rer

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    Jul 31, 2015
    Hey Chris, first of all than you. Yes, very similar as very much exact, except mine has a hardwire +jack. I'd like to focus on the jack itself. Is there a way to extract an output when I flip the switch into "on" position?

    I know that I can probably get a signal if I speak into it. I'd rather not. My problem lies in detection, w/o sound.
     
  4. AnalogKid

    AnalogKid

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    Jun 10, 2015
    What is the resistance of the microphone output pins with the switch in both positions?

    ak
     
    rer likes this.
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I have 2 questions:

    1) Why?
    2) What defines "turned on"
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I have 2 questions:

    1) Why?
    2) What defines "turned on"
     
  7. rer

    rer

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    Jul 31, 2015
    @AnalogKid around 2 Ohms. Can't get much current. I think the large portion of the jack is negative and output, but I thought output was supposed to have some current...

    @Steve "turned on" is the switch in the on position. I guess it activates the sound signal that is then transformed...
    As to why, it bothers me that I can't find solution. I though this would be a simple build. Nope.
     
  8. rer

    rer

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    Jul 31, 2015
    Might be more than 2 ohms, I'll retest in the morning...
     
  9. AnalogKid

    AnalogKid

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    Jun 10, 2015
    The resistance across the balanced output pins should be different in the on and off positions. This *might* be detectable with what is basically a very low current ohmmeter circuit/comparator. A potential problem is that many microphone input circuits have a low input resistance, and this might mask what you are trying to measure.

    ak
     
  10. Alec_t

    Alec_t

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    Jul 7, 2015
    According to the datasheet :-
    Impedance: 600 Ohms ± 30 %

    Does the switch
    a) disconnect the mic internally from the cord,
    b) short the mic or
    c) control power to an in-built pre-amp?
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    My guess is that the mic switch (when OFF) would open the connection to the voice coil and short the audio lines to the amp input. But this is just speculation. You should be able to confirm this with an ohmmeter. You should read ~ 600Ω (Switch ON) and ~ 0Ω (Switch OFF).

    Chris
     
  12. rer

    rer

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    Jul 31, 2015
    Wow, I see. Getting very low resistance when "on" and nothing when "off". My meter might be cheap.

    Pins are shorted in both "on/off" position.

    Edit: getting roughly 300 ohm. (neighbor is electrician ftw)


    So, does this mean there is a current flowing?
     
    Last edited: Aug 1, 2015
  13. Alec_t

    Alec_t

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    Is that 'nothing' as in infinite resistance (open circuit), or 'nothing' as in zero Ohms (short circuit)?
     
  14. rer

    rer

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    Jul 31, 2015
    zero ohms and short circuit

    Edit: or it might be inf resistance. Wow, I honestly don't know at this point.
     
    Last edited: Aug 1, 2015
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    rer, judging strictly by your replies the bigger problem might be understanding us. If we give you possible solutions will you be able to execute it?

    Many topics begin like this one and progress into various solutions described by text and schematics that we will post. The OP must be able to comprehend us, read schematics and be proficient with a soldering iron. Are you up to it?

    Chris
     
  16. rer

    rer

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    Jul 31, 2015
    Yes, I will and I am. I really want to know how to do it. I want to get to the point where, I myself is able to provide solutions. I, personally, code for the most part and something like this is so much greater... I thought I can do it easily, no problem.
     
    Last edited: Aug 1, 2015
  17. Alec_t

    Alec_t

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    Well the solution depends critically on what the action of the mic switch is, i.e. does it short the amp input to ground or not.
     
  18. rer

    rer

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    Jul 31, 2015
    The switch when it's "on" does not short. It does short when "off", also a lot of res when off.

    Here is what I've figured so far:

    I can get current if I create a circuit where mic. would draw current to. I have resistance, impedance so theres got to be current that is enough for a small transistor to switch.

    I've also learned quite a bit.
     
    Last edited: Aug 1, 2015
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, what you have written above indicates you should step away from the microphone and first learn some basics.

    Grab your multimeter. You should be using it on the Ω range.

    If it's switched to this range, with the probes not touching anything it should display OL. This means open. This can also mean a very large (near infinite for our purposes) resistance.

    Now touch the metal part of the probes together. the meter will display 0 (or occasionally a very low value like 0.2). This is a short, or something equivalent to it for our purposes. This means there is essentially NO resistance.

    Now hold the metal part of the probes, one in your left hand, and the other in the right. Squeeze tightly. You should see some figures on the meter. This is an indication of some resistance between a short and open. It does not matter in this case what the actual values are, but when measuring your microphone it will.

    Can you confirm when you've done this and the values you saw.
     
    CDRIVE likes this.
  20. rer

    rer

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    Jul 31, 2015
    roughly 200 ohm
     
  21. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Read what I asked you to do, and do it please.

    *THEN* we'll ask you the open/shorted question again.
     
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