switch electric microphone with relay

Discussion in 'General Electronics Chat' started by bug13, May 11, 2016.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi guys

    I need to switch multiple (only show 2 in drawing, I need to switch up to 5) electric microphone with relays, I have a couple solution, which one do you think is better avoiding loud thump on switch.

    Thanks guys.

    Or, do you have other better options?

    IMG_0981.JPG
     
  2. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Instead of mechanical relays, you may wish to consider implementation of your scheme via, for instance, CD4066s...
    Sometimes the easy way is the best way!:)

    Best regards
    HP
     
  3. #12

    Expert

    Nov 30, 2010
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    Solution one looks right.
    But I don't know why you would want the mics to have floating grounds when not active.
    If you float the grounds, every mic will develop a charge that you can't un-thump.
     
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  4. Hypatia's Protege

    Distinguished Member

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    Agreed! -- That said, I maintain my assertion that employment of analog multiplexers (e.g. CD4066 - in this instance, in conjunction with 'spoiler' resistors) represents the best approach -- Then too there is the added 'bonus' implicit in obviation of the relay-driver requirement...

    Again, this is one of the rarest circumstances to wit: one in which the right way is the easiest way!!!:):):)

    Best regards
    HP
     
  5. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi Hypatia

    Thanks for your replay. I have never used an analog switch. Will the on resistance a problem in my application?
     
  6. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    The mic will have leads a few meters away. If I don't disconnect the ground, will that pick up extra noise (to a level that not acceptable) ?

    And how's that can't in-thump.
     
  7. Hypatia's Protege

    Distinguished Member

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    Inasmuch as said parameter is generally < 200Ω, there should be no problem at input impedances typically encountered in AF amplification applications...

    Note that for lowest R_on, the devices should be powered at design maximum VDD (nominally 15V)
    Here is a link to specs for a typical device of the referenced type...

    Best regards and good luck!
    HP:)
     
    Last edited: May 28, 2016
  8. #12

    Expert

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    Look at solution 1. The resistor keeps the input side of the signal at zero DC from one wire to the other. If you let the wires come loose from ground they will a) pick up static charges and b) won't be equalized to ground. Every time you connect the ground, they have to equalize their DC voltage. Since you can't connect the ground without connecting the ground, the microphone wires will equalize their charge every time you connect them to ground.
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Un-thump? Bells can't be un-rung but microphones can be un-thumped. Interesting.
     
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  10. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi #12,

    Thanks for explanation, I didn't know it can pick up static charges (I know about static charges, but never connect it this way). Learn something new everyday!

    Thanks again!!
     
  11. #12

    Expert

    Nov 30, 2010
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    Even if you don't have static problems, the connection from Vcc will charge the whole mic assembly to Vcc.
    The electret element is a capacitor, but it comes equipped with a j-fet amplifier. That transistor will charge the ground line to Vcc.
    When you plug in the audio wires, that DC potential will discharge.

    http://industrial.panasonic.com/cdbs/www-data/pdf/ABA5000/ABA5000PE44.pdf
     
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  12. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Linear Technology and Maxim make analog multiplexer ships specially designed to switch audio without introducing a thump or click.

    Do you want to switch multiple microphone elements into one mic preamp, or preamp each mic and then mux the higher signal levels?

    What are the shortest and longest cable runs for these microphones?

    ak
     
  13. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    From my testing, I think I need to preamp each mic and then mux the higher signal level. Because the far end is eight too quite, or too much background noise if I turn up the digital gain. (I am not sure where is this background noise from, I am still investigating it, but I am guessing it's either pick up by the long cable, or bad SNR of the MIC)

    The shortest could be 3-4 meters. Longest could be up to 10m.

    NOTE: the cable I am test with is shielded cable, it's about 15m long.
     
  14. AnalogKid

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    Adafruit has two microphone preamp modules. One is based on a Maxim mic preamp chip that has a bias output for an electret cartridge and a built-in AGC circuit.

    Also, since I'm a bit late to the party, what controls the relays or other switching devices? Can you post a basic block diagram showing how you think your various elements will interconnect?

    ak
     
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  15. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    It's very simple, let me descript it first. (easier than drawing)

    Think of it as an intercom, there is one mic and one speaker. But instead of one mic and one speaker, I have 5 mics and 5 speakers connect to the intercom. And a user can select which set is enable, all others are disable. There is only allow one enable at one time.
     
  16. AnalogKid

    Distinguished Member

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    So if two microphones are up to 20 m apart, where is the switching function located? Also, you've asked only about switching the mic. Are you switching the speakers, or do all speakers get the signal from whichever mic is selected?

    ak
     
  17. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    The switching is located at the input of a intercom. And yes I am switching the speakers too. And yes, all speaker will be switch on if the mic next to the speaker is enable.
     
  18. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    If people are speaking very close to the speaker, a speaker can work as the microphone for the sending station (when "talk" button is pressed). Then work as a speaker when the button is not pressed at that station. The high notes are a bit muddled but it is an interesting project.
     
  19. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    We already have a intercom, and we want duplex communicate. So this is out of the picture, it would be an interesting project tho :)

    edited:
    And we need the mic to be able to pick up a conversation from at least 1M away.
     
    Last edited: May 13, 2016
  20. AnalogKid

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    Something to consider when choosing the microphone element...

    While there are many microphones to choose from, and they vary greatly in their absolute sensitivity, they basically do not vary in their relative sensitivity. Using strange numbers that make this point easier to see... let's say mic A makes a 1 V signal when you are 6 inches away, and a 0.5 V signal when you are three meters away. If mic B has 1/10 the sensitivity and makes 0.1 V when you are 6 inches away, then it probably will make very close to 0.05 V when you are 1 m away. With a little extra gain for mic B, the two will be electrically very similar, sensitivity patterns and frequency response being equal.

    ak
     
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