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Rotational sensor that turns off motor

 
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MakeThisSense
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Joined: 08 Oct 2008
Posts: 5

PostPosted: Wed Oct 08, 2008 6:22 pm    Post subject: Rotational sensor that turns off motor Reply with quote

I need to have a motor turn off after turning a specific number of times, the number of times able to be set and reset, and the device having to be battery-powered.

I'm thinking of having a rotational sensor that turns off the motor after a specific number of turns, but I have no idea how to tell the sensor when to turn the motor off or even how to make the sensor turn the motor off. Help!
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Wed Oct 08, 2008 6:50 pm    Post subject: Reply with quote

What speed and size is this motor.

If the motor will be turning very fast and needs to have a precise number of rotations a brake may be needed.

Depending on the speed of the motor an optical sensor or inductive sensor could be used.

Depending on the motor current a transistor or relay could be used to turn it on and off.
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MakeThisSense
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Joined: 08 Oct 2008
Posts: 5

PostPosted: Wed Oct 08, 2008 7:40 pm    Post subject: Reply with quote

The motor is about a fourth the size of a fist and won't be going very fast. The device doesn't have to be particularly powerful, but it does need to stop with great precision.

Would it be possible to have an optical rotation sensor that counts revolutions and opens a relay once it hits a certain number of rotations to break the loop and turn off the motor? Is there any way that an optical sensor can be programmed multiple times by a computer, then disconnected and run battery-powered? I found many sensors online, but none that could be programmed.

I could of course make my own sensor (I already have a light and sensor and a clear plastic disk with dark lines to block light), in which case I'd need one chip that can be programmed with the number of counts I need, one chip that counts the number of pulses from the sensor, and a third chip to compare the two and shut off power when the two are equal. Unfortunately I don't know how to build these. Do you know of any resources that can teach me?
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Wed Oct 08, 2008 8:20 pm    Post subject: Reply with quote

What RPM will that motor be running at?

Look into using a microcontroller to control this. One line could be used to read in the status of the optical sensor, one line could control a transistor that could activate a relay for motor control.

If you need to adjust the number of rotations you could have an up and down button or simply reprogram the chip if it doesn't need to change very often.

Have a look here for some microcontroller resources
http://forum.hackedgadgets.com/viewforum.php?f=15
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MakeThisSense
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Joined: 08 Oct 2008
Posts: 5

PostPosted: Wed Oct 08, 2008 8:40 pm    Post subject: Reply with quote

The number of rotations will change very often, and will vary a great amount.

I'm not sure how many rotations per minute the motor will have, but right now I'm using a motor from a printer, if that's any hint.

Thanks for recommending a microcontroller; I'll start learning about them. Smile
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MakeThisSense
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Joined: 08 Oct 2008
Posts: 5

PostPosted: Wed Oct 08, 2008 9:32 pm    Post subject: Reply with quote

So I read through that post on instructables.com and the Zilog Z8 is looking very attractive, especially since it can just be connected to my laptop. I liked the SunSPOT since I already know how to program in Java, but that seems pretty expensive and way too fancy for the project I'm doing. Would the Zilog be good for a complete beginner who can only program in Java and C++? How much learning and adapting would I have to do, and how user-friendly is it for a beginner without an already knowledgeable person standing by to teach her?
Also, would you recommend the 4/8-k or the 16-64 k chip?
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