555 timer problem/ question

Discussion in 'General Electronics Chat' started by itel933, Oct 6, 2010.

  1. itel933

    Thread Starter Member

    Aug 26, 2010
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    0
    I am using this schmatic. I have eliminated the red led, and buzzer and instead put a micro vibrator in its place. I have 2 problems:

    1) When I immediatly turn on the unit the micro vibrator vibrates very slowly and I have the cycle the on and of switch a few times in order to stop it from vibrating.

    2) if I tap the housing that I made for the circuit the vibrator starts to vibrate.

    what am i doing wrong?
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    What is the current drawn by this micro vibrator?
    Depending on the brand and type of 555 the maximum current is 200 mA.
    Cmos versions are limited even more.

    The case when you tap the housing looks like a bad contact.

    Bertus
     
  3. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    its a radio shack part # 273-0107
    3vdc 95mA

    BTW Im using a 556 chip (im told the 555 and 556)
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    The NE556 is a dual version of the NE555.
    Can you redraw your circuit and correct the pin connections?


    [​IMG]

    [​IMG]

    Bertus
     
  5. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    sorry what I meant to say is that i was told the 555 and the 556 are identical only difference being that the 556 has 2 555. I have all of the pin connections right and all of the connections. anything else I should be looking for?
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    I have redrawn the circuit for you with the NE556.
    The numbers between the brackets are for timer 2.

    [​IMG]

    Did you use the correct pins?

    Bertus
     
  7. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    still having the same problem...what could it be

     
  8. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    It's probably a good idea to put a capacitor across the power supply terminals, in the range of 47µF to 220µF. Especially if the battery is low, the voltage could drop when the vibrator turns on.
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I sensed a disturbance in the force.

    What you've gotten so far is good advice. Add a capacitor to pin 3, around 0.1µF. This is the Control pin, and is used to suppress noise in a very critical part of the 555 circuit. Also ground pin 10, the reset pin on the second 555 inside the package.

    You would also benefit by separating the beeper from the LED, give the red LED it's own resistor, and have the beeper going between Vcc and the output (pin 5). If the beeper needs a resistor to reduce the voltage on it add one. The reason I think this is so is the beeper isn't really a controlled current. It might work as is just fine, but I'm not comfortable with it.

    http://forum.allaboutcircuits.com/picture.php?albumid=41&pictureid=308

    http://forum.allaboutcircuits.com/picture.php?albumid=41&pictureid=977
     
  10. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    bill i removed the red led, and the beeper. In its place I just have the micro vibrator. BTW itstead of a 220uf cap I'm using a 10uf. the reset is not connected.

     
  11. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    That vibrator is a powerful electrical noise maker. So is an unconnected network of digital gates like the spare 555. You need to suppress the second 555 completely to make sure it is quiet.

    Actually I would ground Pins 8, 10, 12, and 13 to make sure that part of the chip isn't doing anything you don't want it to do.

    The extra caps (all of them mentioned) will help quieten things down.

    That vibrator is a motor. It is a lot like a relay. Devices like these need a diode to suppress what could be some intense counter EMF voltage spikes that will put the semiconductor driving them at risk.

    [​IMG]

    We can advise, it is up to you if you want to follow it. Even simple designs like yours I generally breadboard first. It allows you to add and remove components until is works like you want it to.
     
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