on/off buzzing sound

Discussion in 'The Projects Forum' started by telerian, Sep 4, 2010.

  1. telerian

    Thread Starter Active Member

    Jul 19, 2010
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    I want to make a circuit that would generate a sound that goes on and off on a regular interval this is to be used with an automated door as a warning that the door is moving. I want to connect this circuit on the same relay that is controlling the dc motor moving the door, the relay powers the motor with 36 VDC. The sound should be there as long as the door is moving (in either direction).
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_140695_-1


    You would need to make a simple resistor voltage divider network to give you 12 volts and about 20 mA from the supply of 36 volts. You would take the voltage sent to the motor divide it in a 2 to 1 ratio to get the 12 volts.

    a 1200 ohm resistor and 600 ohm resistor connected in series from the positive lead of the motor to the powersupply ground will give you 12 vdc and 20 mA at the junction between the the two resistors. Put the buzzer from the link above there. Red wire connected to the resistor junction and the black wire connected to powersupply ground.(or across the 600 ohm resistor)

    getting the on/off repetition would involve more circuitry than I describe. Is on/off required by a law or something? wouldn't a steady sound that is present when the door is moving work just as well?

    Kermit2
     
    Last edited: Sep 4, 2010
  3. KMoffett

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    Dec 19, 2007
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  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I think some Mallory Sonalerts operate off of 36V, if not it's a simple matter of adding a zener in series with whatever you choose providing you're running this off of DC.
     
  5. telerian

    Thread Starter Active Member

    Jul 19, 2010
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    First of all thank you for the tip, the only reason for the on/off is not have an annoying steady tone. I was thinking of using a 555 timer for the on/off but the problem is the 36V supply
     
  6. telerian

    Thread Starter Active Member

    Jul 19, 2010
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    They have great products, one of the products works up to 48V and does "Continuous, Slow Double Beep, Quick Beep, Fast Warble" but unfortunately we don't have that in Egypt
    This http://ram-e-shop.com/test11/product_info.php?cPath=91&products_id=562 is something that is found here but am not sure if 70db is loud enough
     
    Last edited: Sep 5, 2010
  7. Dyslexicbloke

    Active Member

    Sep 4, 2010
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    You will find reversing bleepers, designed for tractors and trucks all over the world.
    They will be 24VDC, one of these and a simple voltage reg will do the job easily.
    Al
     
  8. KMoffett

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  9. marshallf3

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    Jul 26, 2010
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    Some reason you can't have things shipped to Eqypt?

    I'll agree, 70 dB isn't much at all, you're going to want 90 or so and the places like Mouser, DigiKey, Jameco etc all have these beeper/buzzers available with the on/off beeping as part of their d=internal design. I also wouldn't worry about the voltage, if you've got 36V and your selected beeper only works up to 24V just put a 12V zener in series with it.
     
  10. telerian

    Thread Starter Active Member

    Jul 19, 2010
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    This is a great idea but there is one problem, the voltage going to the DC motor is is either +36 or -36 depending on the direction of rotation of the motor
     
  11. Kermit2

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  12. KMoffett

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    Dec 19, 2007
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    Or a bridge rectifier. ~/~ terminals to the motor power...+/- to the Sonalert.

    Ken
     
  13. telerian

    Thread Starter Active Member

    Jul 19, 2010
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    Shipping would be prohibitively expensive from the US to Egypt, it will be more than the value of the product itself
    Would the Zener be able to handle the current required by the buzzer/beeper ?
    What about the polarity reversing ?
     
    Last edited: Sep 6, 2010
  14. telerian

    Thread Starter Active Member

    Jul 19, 2010
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    I am not sure I understand you correctly, the 36V are DC not AC
     
  15. Oupajohn

    New Member

    Sep 6, 2010
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    + or - voltage can be sorted woth a good oldfashioned rectifier bridge. Your input goes to the AC side (even though it's DC you're putting in), and lo and behold you'll get DC only one way at the other end.
    The bridge will rectify AC, no matter what the frequency - 50 Hz, 1 Hz, once a day . . .
     
  16. marshallf3

    Well-Known Member

    Jul 26, 2010
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    He's got 36 VDC driving a motor and the polarity reverses to reverse the motor.

    The bridge rectifier is a good solution and as to the zeners you'd only need one that way.

    Hook the (~ )(AC input) terminals of the bridge rectifier across the motor terminals.

    Hook the K (cathode) band of the selected zener diode to the (+) output of the bridge rectifier and the other end to the (+) input of the buzzer.

    Hook the (-) terminal of the bridge rectifier to the (-) terminal of the buzzer.

    Select your zener voltage based upon how many volts you need to subtract from the 36V to get into the safe operating area of the buzzer.

    After dealing with shipping to quite a few international countries is Post is by far the preferred way to go. http://www.mouser.com will ship via Post and can provide you with a quote over the phone if you call them with the oart nubers you need, however the only components required for this circuit are the type that any normal Radio Shack (or your equivalent) would carry on their shelves.
     
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