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Trying to wire a mic preamp with a switching circuit. Help!

Discussion in 'The Projects Forum' started by sheffner, Oct 4, 2009.

  1. sheffner

    Thread Starter New Member

    Oct 2, 2009
    Hello. I'm trying attempting my first electronics project and need a little help. The project is a key finder(I'm aware you can buy them). So far I know I need to make a mic preamp circuit and a switching circuit. I was just wondering how to put the 2 together. The diagram shown is for a switching circuit, and I wanted to know if I can put the mic preamp circuit in where the transmitter is supposed to go instead. Would that work?
    And here are my parts:
    1 piezo buzzer
    4.7kOhm resistors
    220kOhm resistors
    2.2kOhm resistors
    NPN switching transistors
    10uf capacitor
    100uf capacitor
    condensor mic
    red led
    2N3055 transistor

    Am I on the right track atleast? I also uploaded the mic preamp diagram I'm using if anyone needs it... Thanks a lot!
  2. Audioguru


    Dec 20, 2007
    You don't show a switching circuit. You show a 5V power supply and a mic preamp.

    The 5V power supply will not work for long because it uses an ordinary 5V regulator that needs an input at least 7V and the 9V battery will quickly drop to 7V then the regulator will fail.
    You need a low-dropout 5V regulator with a 9V battery because the low-dropout regulator still works perfectly when the battery has dropped to 5.5V. But your circuit probably does not need a regulator.

    A 2N3055 is a huge very high power transistor that you don't need. You need a BC547B or a 2N3904 transistor.

    You do not want a condensor mic that is powered from a high voltage supply. You want an electret mic that has the high voltage built-in when it is made.
  3. tibbles

    Active Member

    Jun 27, 2008
    hi shefner
    im newish to electronics but a couple of points, are you triggering the alarm by whistling or are you building a small transmitter?
    i think if you are relying on a whistle you will need another stage of amplification,
    also the output of your circuit will be your whistle, normally i believe these things have an alarm output.
    i dont see the need for the switch/ voltage regulator at this stage anyway.
    im sure you will get more knowledgeable answers
    regards dougal
  4. tibbles

    Active Member

    Jun 27, 2008
    sorry audioguru ididnt want to clash with your reply,apologies.
  5. sheffner

    Thread Starter New Member

    Oct 2, 2009
    Thanks for saving me again Audioguru! :p
    Ok, I'm an idiot, I actually do have the 2N3904 transistor, I wrote the wrong one down. See I thought I had an electret mic, I looked it up at radioshack.com and gave them the electret mic # but they gave me the condensor mic apparently. Like I said, I'm very very new! :p Thank you so much for all your help so far! So could I use the same circuit and just drop out the voltage regulator? And how would I combine the 2 circuits? I think I'm finally understanding the schematics, just not exactly sure where to combine them. But as far as parts I just need to get the electric mic and i'll be good right? And I'm trying to make it respond to whistling. Thanks for your help tibbles! You may be new too but you're leaps and bounds ahead of me! :p Thanks for everyones help!!!