pick-up's motor cc

guyzard · 5th May 2009, 07:58 PM

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:

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 !)

Steerpike · 5th May 2009, 10:39 PM

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.

guyzard · 6th May 2009, 02:33 PM

hi,

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

In your opinion, what is the best interesting between the NE555 and the LM317 ? Is the torque is good with a LM317 ?

Steerpike · 6th May 2009, 11:01 PM

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!

guyzard · 7th May 2009, 01:52 PM

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

guyzard · 8th May 2009, 01:00 AM

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 !!

Steerpike · 8th May 2009, 01:57 PM

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.

guyzard · 8th May 2009, 05:06 PM

like this ?

Steerpike · 8th May 2009, 05:15 PM

Yes, exactly like that :-)

guyzard · 8th May 2009, 11:23 PM

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.

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

seeing of the up:

the settings (1 of 2 variables resistances only):

the switch:

Perspectives:

bearings:

5th May 2009, 07:58 PM	#1
guyzard diyAudio Member Join Date: May 2009	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: 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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6th May 2009, 02:33 PM	#3
guyzard diyAudio Member Join Date: May 2009	hi, Thanks for your answer ! I just create a diagram with the NE555, and my simulation is runnable ! In your opinion, what is the best interesting between the NE555 and the LM317 ? Is the torque is good with a LM317 ?

6th May 2009, 11:01 PM	#4
Steerpike diyAudio Member Join Date: Jan 2006 Location: Johannesburg, South Africa	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!

7th May 2009, 01:52 PM	#5
guyzard diyAudio Member Join Date: May 2009	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

8th May 2009, 01:00 AM	#6
guyzard diyAudio Member Join Date: May 2009	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 !!

8th May 2009, 01:57 PM	#7
Steerpike diyAudio Member Join Date: Jan 2006 Location: Johannesburg, South Africa	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.

8th May 2009, 05:06 PM	#8
guyzard diyAudio Member Join Date: May 2009	like this ?

8th May 2009, 05:15 PM	#9
Steerpike diyAudio Member Join Date: Jan 2006 Location: Johannesburg, South Africa	Yes, exactly like that :-)

8th May 2009, 11:23 PM	#10
guyzard diyAudio Member Join Date: May 2009	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. I have make a 3d solidworks simulation, too. I haven't finish the arm. seeing of the up: the settings (1 of 2 variables resistances only): the switch: Perspectives: bearings:

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