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Control Voltage and motors...
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JAMESveeder



Joined: Nov 16, 2010
Posts: 34
Location: tucson

PostPosted: Fri Nov 02, 2012 1:20 am    Post subject: Control Voltage and motors...
Subject description: Possibly a simple question
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Okay, so I had a question about changing motor speed via control-voltage.

Is it possible?

Basically what I'm doing is I'm working on an analog sequencer based off of the Baby 10 sequencer. I would like to use the CV out of the sequencer to control the speed of a motor. (To be more specific, I want to control the speed of a cassette player motor)

I have no idea how to do this, or even what to google for that matter as I feel like the search "control motor with control voltage" is too broad and doesn't really bring up much.

So, some input from you guys would be great. I hope it's easy!

Thanks guys.
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Sebo



Joined: Apr 27, 2007
Posts: 540
Location: Argentina

PostPosted: Fri Nov 02, 2012 8:23 am    Post subject: Reply with quote  Mark this post and the followings unread

I think that you have to control the speed of the motor via PWM, Google for motor PWM control or something like that.
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bubzy



Joined: Oct 27, 2010
Posts: 555
Location: United Kingdom
Audio files: 62

PostPosted: Fri Nov 02, 2012 9:08 am    Post subject: Reply with quote  Mark this post and the followings unread

this will depend on the type of motor you are using. im pretty sure that with a dc motor, the amount of voltage in controls the speed of the motor, you would have to have some kind of buffer after the sequencer output.
easy way to test the motor, is just wire it up to a potentiometer as a voltage divider and give it a whirl Smile

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Sebo



Joined: Apr 27, 2007
Posts: 540
Location: Argentina

PostPosted: Fri Nov 02, 2012 9:25 am    Post subject: Reply with quote  Mark this post and the followings unread

The problem of lowering the voltage is that you are lowering the power, so at some point you can't move the tape anymore.
PWM minimizes that problem.

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syntherjack



Joined: Oct 29, 2012
Posts: 21
Location: Poland, Poznan

PostPosted: Fri Nov 02, 2012 9:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Hallo,
cassette player uses for 99% DC motor, so you need:
- voltage controlled PWM modulator (generator),
- motor driving circuit (BUZ11 or L293 based).

LTC6992 will do the thing for voltage -> PWM conversion, for another solution search under "(analog) voltage controlled PWM generator". There are many circuits out there, also 555 based.

Jack
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Thomas_Henry



Joined: Jul 24, 2009
Posts: 129
Location: N. Mankato, MN

PostPosted: Sun Nov 04, 2012 1:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Gang,

PWM is the best way to go to avoid dissipation problems and reduced torque. It's easy to do. Attached is a one chip solution I whipped up on the workbench. I used the PICAXE 08M just because I had some laying about. The more modern 08M2 could also be used.

I've shown two different options, one using a Darlington and the other using a power MOSFET. Either works quite well and both run cool. A pot is used to provide the control voltage, but this could be provided by a synth. The range is 0 to +5V and controls the motor from 15% to 99% full power.

Also attached is the code. It ended up being 32 bytes long, so there's a lot more space left over for any modifications you have in mind. There are also some extra port pins.

Remember, the Program Editor for this chip is free, and the "programmer" is nothing more than a cable---total outlay: $4 for jacks and wire.

Finally, I've attached a photo of my test rig. Hope that gives you some ideas.

Thomas Henry


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JAMESveeder



Joined: Nov 16, 2010
Posts: 34
Location: tucson

PostPosted: Mon Nov 05, 2012 1:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow, I appreciate all of the replies, and thanks for the thorough reply, Thomas_Henry!

So essentially what I would need to do is take the control voltage from the sequencer, convert that into a pulse width signal (which I'm assuming is just taking the square pulse coming from the sequencer and changing the duty cycle based on voltage?) and differing duty cycles will change the speed of the motor, am I right?

Forgive me if I'm not getting this, the learning curve for DIY electronics is quite steep in my opinion haha.
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bubzy



Joined: Oct 27, 2010
Posts: 555
Location: United Kingdom
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PostPosted: Mon Nov 05, 2012 3:48 am    Post subject: Reply with quote  Mark this post and the followings unread

JAMESveeder wrote:
So essentially what I would need to do is take the control voltage from the sequencer, convert that into a pulse width signal (which I'm assuming is just taking the square pulse coming from the sequencer and changing the duty cycle based on voltage?) and differing duty cycles will change the speed of the motor, am I right?


yep, if you use thomas's circuit you will have to make sure that you scale your voltage down to 0-5v though, and just use your "CV out" into pin 6

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JAMESveeder



Joined: Nov 16, 2010
Posts: 34
Location: tucson

PostPosted: Tue Nov 06, 2012 4:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay, sounds good, thanks for the heads up.
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