Micro vibrator with 555 IC

Discussion in 'General Electronics Chat' started by itel933, Nov 7, 2010.

  1. itel933

    Thread Starter Member

    Aug 26, 2010
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    I have a micro vibration motor that is rated at 3VDC, 95mA. I have connected one lead to the output of the 555 and the other lead to an LED that is connected to the Vcc. Do I need a resistor in series with the vibratotor? The 555 is being powered by a 9 volt bat
     
    Last edited: Nov 7, 2010
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    When the output of the 555 goes low, supply voltage will be applied to the vibrator minus the Vol of the 555. With Vol being pretty close to zero, you can ignore it. You will need a resistor to drop the voltage difference between your supply and 3 volts. R= E/I= (Vsup-3)/95ma.
     
  3. itel933

    Thread Starter Member

    Aug 26, 2010
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    so then Ill need a resistor of 63 ohms in order for the vibrator motor not to burn out? Not sure what you meant by all you wrote in your response. will the resitor (470 that already on the output serve as my resistor for the vibrator or do I need to have a separate resistor? Sorry Im new

     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    I can't seem to pull up the picture of the circuit, however ....

    You can go down as low as 63 ohms. If you're running well enough as it stands why mess with it?
    Then again, you might try a 100 ohm just to see what the difference is.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    896
    A DC motor is almost a dead short when it starts running. The current is limited to about 111mA by the (2.0V) red LED and 63 ohm resistor which will instantly burn out the red LED.
     
  6. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    When I responded to this yesterday there was no drawing and no mention of the LED. Of course things are different now.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    Did you notice the 50M(!) timing resistor? A regular 555 has a max resistor value of 20M so this 555 might be a Cmos LMC555, TLC555 or ICM7555 with a very low output current that cannot drive the motor.
     
  8. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    should I be concerned with the 50M? I used a 556 that I bought from Radio shack. Will that resistor cause a problem later on? As of right now it works fine and gives me the time that I want. What happens if I leave it the way it is? Should I be using one of these other chips instead?

     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The input current of the 555 dictates that 20M is maximum. The leakage current of the capacitor dictates that 20M maybe is too high.

    A Cmos 555 has no input current but the capacitor still has leakage current. If you use very expensive and huge film capacitor then it might time correctly, but the output current from a Cmos 555 is too low.

    I EDITED the leakage currents.
     
    Last edited: Nov 8, 2010
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