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Dimmer circuit help

Discussion in 'General Electronics Discussion' started by angelodp, Nov 17, 2012.

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  1. angelodp

    angelodp

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    Feb 3, 2010
    Hi, I am working on a circuit for a dimmer that will control a pickup winder ( guitar pups ). I have built the unit and it works, but the potentiometer in this circuit does not cut out the voltage completely. The DC motor stills get voltage, even with the pot turned off, and so the motor still turns. albeit veery slowly. Ideally, I would like to use the pot to stop the motor completely. Any help would be greatly appreciated.

    Thanks A

    [​IMG]
     
  2. duke37

    duke37

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    769
    Jan 9, 2011
    If I remember rightly, an LM317T controls with 1.25V btween the output and the control terminal so the minimum output in your circuit will be 1.25V, hence the motor not stopping.

    You can drop 0.6V with a silicon diode (1N400x etc.) so a couple of diodes in series with the motor will stop it.
     
  3. angelodp

    angelodp

    19
    0
    Feb 3, 2010
    thanks

    Hi Duke, ok great, so can that happen on either side of the motor? I reckon on the + side with the flow into the motor.

    A
     
    Last edited: Nov 17, 2012
  4. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Try one diode first, that may be enough and will not drop the maximum voltage so much.

    I would put the diode in the positive wire to the motor, I like to keep the ground connection at ground all along the diagram. Just for neatness.

    You have a very good motor if it will run on only 1.25V.
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    Perhaps a more elegant solution would be replacing your pot with a model that incorporates an integral switch. It can replace the power switch in your schematic.

    On the other hand PWM makes a much better motor controller than a linear regulator.

    Chris
     
  6. angelodp

    angelodp

    19
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    Feb 3, 2010
    Yup

    Ok that one diode did the trick.

    A quick question if you can. Would you happen to know if anything can be done to a typical reed magnetic switch to increase its accuracy and rpm specs. I have some typical reed magnet switches that seem to be pretty accurate up to about 1500 rpm, then after that I am not too sure. is there anything that can be done to make the switch more sensitive?

    Best A
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    Yes... replace it with a Hall effect sensor!
     
  8. angelodp

    angelodp

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    Feb 3, 2010
    more info

    Ok, so a hall effect sensor can withstand a greater rpm and maintain accuracy. I looked up some hall sensors but could not find info on what the maximum rates of revolution would be. Can you suggest a specific type. I am using this for a pickup winder and would like to be able to go from 0- 3200rpm and accurately count all the turns.

    Best
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    They will easily handle that. No bounce or float either.

    Chris
     
  10. angelodp

    angelodp

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    Feb 3, 2010
    recommend

    Can you guys recommend a particular hall sensor.

    A
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Not without details of your application. You can choose one - go for one that's cheap, a good fit mechanically, and will work from the supply voltage that you have available.
     
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