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Dimmer circuit help

angelodp

Feb 3, 2010
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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

Winder-schemo.jpg
 

duke37

Jan 9, 2011
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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.
 

angelodp

Feb 3, 2010
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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
 
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duke37

Jan 9, 2011
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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.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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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
 

angelodp

Feb 3, 2010
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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
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Yes... replace it with a Hall effect sensor!
 

angelodp

Feb 3, 2010
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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
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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and would like to be able to go from 0- 3200rpm and accurately count all the turns.

Best

They will easily handle that. No bounce or float either.

Chris
 

KrisBlueNZ

Sadly passed away in 2015
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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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