Replace speaker of alarm clock with dc motor

Discussion in 'The Projects Forum' started by sadiq3210, Sep 14, 2014.

  1. sadiq3210

    Thread Starter New Member

    Jun 14, 2013
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    hi.
    I want to replace speaker of table alarm clock with dc motor for some reason.
    It uses 1.5 volts AA battery.
    I cut the speaker wires, multi-meter show the dc voltage that goes up to 0.8 while fluctuating.

    when i connected two terminals to dc motor, it do not run.
    What to do ?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    First, you can post what is the voltage and current rating of the motor?
     
  3. sadiq3210

    Thread Starter New Member

    Jun 14, 2013
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    The resistance of motor is 1.2 ohm, Is that enough?
    If not, then tell me how do i find the voltage and current rating ?
    There is no label on the motor.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Well, 1.2 ohms requires a startup current of over an amp from a 1.5V source which likely can't be provided by the speaker output amp.

    Does the motor run if connected directly to a 1.5v battery?
    If not how much voltage does it take to run as you want?
     
  5. Johann

    Senior Member

    Nov 27, 2006
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    You cannot run a dc motor directly from the speaker wires since the signal resembles AC at some frequency. This needs to be integrated and used to activate, for example, a relay which in turn can connect a separate DC supply to the motor in question.
     
  6. ISB123

    Well-Known Member

    May 21, 2014
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    You're going to need mini DC motor found in cell phones which is used for producing vibrations.
     
  7. Johann

    Senior Member

    Nov 27, 2006
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    You still need dc to run a dc motor (permanent magnet type, I presume).
     
  8. sadiq3210

    Thread Starter New Member

    Jun 14, 2013
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    Crutschow.
    The motor runs when directly connected to 1.5 V battery.

    But i can feel that it runs slow as compared to when it is in original device in which the battery voltage is higher.

    But thats enought for me if it runs slow
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Use a small sensitive AC relay in place of the speaker and a latch contact that can be unlatched by P.B. , the typical cycle start circuit, this way you can switch any voltage you like and a suitable DC level for the motor in question.
    Or a small DC relay fed with a small bridge off the spkr output.
    Max.
     
    Last edited: Sep 14, 2014
  10. sadiq3210

    Thread Starter New Member

    Jun 14, 2013
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    MaxHeadRoom
    any way to amplify the signal using tranister ?
    If no, then why?
    If yes, the how?
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Did you want to run the motor continuously because the speaker signal varies in frequency and amplitude, what about dead air or pauses, there will be zero output, I would have thought that the latching relay or similar would be optimum otherwise the results will vary with signal?
    You could amplify it, but the same situation will occur at zero modulation.
    What does the motor do?
    Max.
     
  12. sadiq3210

    Thread Starter New Member

    Jun 14, 2013
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    No problem if the motor runs discontinously.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The speaker output will not run a DC motor, even amplifying the signal without extra circuitry.
    Max.
     
  14. sadiq3210

    Thread Starter New Member

    Jun 14, 2013
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    If not dc then, Is there any AC motor that can run with or without amplification?

    If not, then, other than amplifying with transistor, what are other options?
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    We are back to post #9 ;)
    Max.
     
  16. ISB123

    Well-Known Member

    May 21, 2014
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    I'm pretty sure that generated alarm wave never drop's below 0V so you basically have half wave AC which means motor will only make half of turn.
     
  17. crutschow

    Expert

    Mar 14, 2008
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    Can you use a separate battery to power the motor or do you want to use the clock battery?
     
  18. sadiq3210

    Thread Starter New Member

    Jun 14, 2013
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    yes, i can use separate battery
     
  19. crutschow

    Expert

    Mar 14, 2008
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    Can you measure the DC and AC voltage coming from the speaker wires? Does this go to zero when the alarm is off?
    Is this alarm a tone or from a radio?
    If you can use a separate battery then you can likely use a transistor amp to turn on the motor.
     
  20. Johann

    Senior Member

    Nov 27, 2006
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    Just use a sensitive relay and latch it on as was suggested, then use the external battery to power the dc motor via the n.o. contact of the relay. Also a N.C. push button to interrupt the current through the latching circuit. Finish!
     
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