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Old 5th May 2009, 07:58 PM   #1
guyzard is offline guyzard  France
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Default pick-up's motor cc

Hi everybody,

I'm making a diy pick-up (with a belt). I will use recuperation pieces.
I want to supply a 12v dc motor.
I have a question, because I am a beginner in the world of the electronic .

I want to use a switch to choose 2 ways ("33 rpm" and "45 rpm") to pilot my motor with 2 signals.

First, I think use a voltage divider (with resistances) connected in series with a potentiometer (to affine the voltage setting)

diagram:

Click the image to open in full size.

Did I make mistakes ? Does the 6 or 8V voltage can damage my 12v motor ?

Out of memories, I can pilot my motor with a transistor and a rectangular signal, but I don't know how to create a rectangular signal (with an editable duty cycle) without a low frequency generator...

If someone can help me, I thank him with avance !

(And I'm very sorry...I'm French and I'm 16 years old...The English electronic vocabulary is so difficult !)
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Old 5th May 2009, 10:39 PM   #2
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Default Re: pick-up's motor cc

Quote:
Originally posted by guyzard

First, I think use a voltage divider (with resistances) connected in series with a potentiometer (to affine the voltage setting)
Did I make mistakes ? Does the 6 or 8V voltage can damage my 12v motor ?

Out of memories, I can pilot my motor with a transistor and a rectangular signal, but I don't know how to create a rectangular signal (with an editable duty cycle) without a low frequency generator...
6 or 8v will NOT damage a 12v motor.

Your circuit will work, but it has some problems. It will be diffficult to compute the resistances for correct speed control - you will need to adjust the variable resistor each time you change speed.
And the usual way to wire a potentiometer (variable resistor) is to take the output from the centre pin (wiper), rather than use that as the input. (I have attached an example)

A problem with this type of circuit using only resistors is that the speed control and speed accuracy are poor, the motor also has a very low starting torque.
Yes you are right, a variable duty cycle square wave is a good method to run motors at low speed. The NE555 ic can do this job - search the web for 555 PWM circuits - you will find many examples.

An alternative is to build a variable DC power supply, using an IC like an LM317 (www for data sheets and application notes). It is simple, just involving one resistor and one variable resistor in addition to the LM317. this will provide a much better speed stabilty than controlling the motor voltage by resistors alone.
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Old 6th May 2009, 02:33 PM   #3
guyzard is offline guyzard  France
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hi,

Thanks for your answer ! I just create a diagram with the NE555, and my simulation is runnable !

Click the image to open in full size.

In your opinion, what is the best interesting between the NE555 and the LM317 ? Is the torque is good with a LM317 ?
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Old 6th May 2009, 11:01 PM   #4
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It looks like a good starting point!
The 555 pulse width modulation method will give better torque at low speeds, and better starting than the LM317.

You may need to experiment with the PwM frequency to find the best match to your motor.

I'll be interested to hear how it works when you've built it!
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Old 7th May 2009, 01:52 PM   #5
guyzard is offline guyzard  France
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OK thanks for your answer !

There is not problems, I'll show it when the pick up is finish.
I have lots of homeworks before july, and the building is going to be slow

See you
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Old 8th May 2009, 01:00 AM   #6
guyzard is offline guyzard  France
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Hello,

I think I have the final version of the diagram.
Maybe I'll add LEDs for the users, and shut-down buttons in the arm of the pick-up.

Tell me what you think about it !!

Click the image to open in full size.
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Old 8th May 2009, 01:57 PM   #7
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It looks good! I would make the 45 and 33 resistors variable, instead of the 100k. That way, you don't need to adjust the 100k each time you change speed - you can have a separate 'pitch control' for each speed setting.
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Old 8th May 2009, 05:06 PM   #8
guyzard is offline guyzard  France
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like this ?

Click the image to open in full size.
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Old 8th May 2009, 05:15 PM   #9
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Yes, exactly like that :-)
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Old 8th May 2009, 11:23 PM   #10
guyzard is offline guyzard  France
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hi,

this evening I have realized lots of stuff...

It was very difficult to make a PCB layer (in french: un typon) for the first time

I belive my typon is good. I put out of the PCB the motor and the variables resistances.

Click the image to open in full size.

I have make a 3d solidworks simulation, too. I haven't finish the arm.

seeing of the up:

Click the image to open in full size.

the settings (1 of 2 variables resistances only):

Click the image to open in full size.

Click the image to open in full size.

the switch:

Click the image to open in full size.

Perspectives:

Click the image to open in full size.

Click the image to open in full size.

bearings:

Click the image to open in full size.
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