Need help on a new project

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biophase
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Need help on a new project

Post by biophase » Mon Aug 17, 2009 10:26 pm

I'm trying to design this device that would measure the pull of my dog on the leash. Basically it would clip between the collar and leash and measure tension. I was thinking of using a simple spring scale to do this, but I purchased a digital fish scale and took it apart. The fish scale has no moving parts and I'm trying to figure out how it measures weight. Looks like a small pressure plate connected to a circuit board. Ideally, this device would beep as the tension exceed a certain number which can be changed. Can anyone think of a better way to design something like this?

Dean Huster
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Re: Need help on a new project

Post by Dean Huster » Tue Aug 18, 2009 5:35 am

What's it going to be? Output of tension gauge interfaced to a shock collar? If the collar is mounted to the dog, it's saying "Don't pull so hard." If mounted to the owner, it's saying, "Lemme go!"
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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reloadron
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Re: Need help on a new project

Post by reloadron » Tue Aug 18, 2009 5:48 am

The fish scale has no moving parts and I'm trying to figure out how it measures weight. Looks like a small pressure plate connected to a circuit board. Ideally, this device would beep as the tension exceed a certain number which can be changed. Can anyone think of a better way to design something like this?
Devices like this generally employ the use of A STRAIN GAUGE, which you can read about in the link provided. Yes, predetermined limits can be set. I think the first step would be to read the link and gain an understanding of a strain gauge and how they work. With that understanding the fish scale should make sense. Actually there are moving parts but the movement is so slight we don't see it like we do with a spring scale or spring tensiometer.

Ron

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Lenp
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Re: Need help on a new project

Post by Lenp » Wed Aug 19, 2009 6:25 pm

Biophase...
Give us some more info, like tension range, accuracy, cost point ...
Are you interested in a high tech gadget or just a crude but a git-er-done job?

You may need to use amplifiers and a comparator to monitor the signal from the strain gauge
or
maybe just use a photo interrupter or microswitch rigged onto a mechanical scale

Many choices and options

Len
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
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kheston
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Re: Need help on a new project

Post by kheston » Wed Aug 19, 2009 7:43 pm

Maybe the fish scale is more technically complex than you need at this point. Perhaps a dog-lead tied to the end of a pull spring, wrapped around a pulley with a potentiometer dial as the axle would be an easier prototype to build? I've never built anything around a strain gauge but I'd imagine the electronics would be more difficult to design than those you'd use with a simple pot.
Kurt - SF Bay

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MrAl
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Re: Need help on a new project

Post by MrAl » Fri Aug 21, 2009 8:58 am

Hello,


Biophase, how big is your dog?
LEDs vs Bulbs, LEDs are winning.

biophase
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Re: Need help on a new project

Post by biophase » Sat Aug 22, 2009 9:43 am

The device is just attached to a collar and would beep or make some noise once the tension passes a certain point. My dog is a german shepherd but this device should be able to work for dogs of all sizes.

Tension could be from 5 to 30 lbs?? I'm not really sure how hard a dog can pull. I should attach my dog to a fish gauge and walk him. I'd like to build something mass produced around $10-$20. It doesn't have to be very accurate at all, just needs the ability to increase or decrease the beeping point.

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jwax
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Re: Need help on a new project

Post by jwax » Sun Aug 23, 2009 3:40 pm

Have to agree with Lenp- a microswitch in a mechanical fish scale whereby the operator can adjust the position of the switch up and down the travel of the spring to beep a beeper at any desired pull force. Cheap, easily manufactured, and effective.
A strain gauge with electronics would cost way too much, unless you have a pal in China willing to build 100,000 of them @ USD$1 each.

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Re: Need help on a new project

Post by Engineer1138 » Mon Aug 24, 2009 10:15 am

If your Shepherd is anything like mine, he can pull a lot harder than 30 lbs. A good guess would be 100lbs for short periods and over 150 for quick bursts.

Anyway, it looks like what you need should be pretty easy to build if it doesn't need calibration. kheston's idea is a good one. A rod running in a sleeve with a spring attached to one end for tension (like a mechanical fish scale) is easy and cheap to build. Add to that a cheap encoder driven by a string attached to the moving rod to measure the movement, a microcontroller to count the pulses from the encoder and a few switches to set the threshold and voila!

What do you want it for? Seems like an unusual project.

lyndon

biophase
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Re: Need help on a new project

Post by biophase » Tue Aug 25, 2009 9:28 pm

I was going to use it as a training device. Dog pulls on leash too hard and it beeps, I stop walking. Dog starts walking again, as soon as it beeps again I stop. Hopefully my dog will begin to learn that there's a certain tension he can pull before I stop walking. Then I slowly lower the tension until he doesn't even pull anymore.

biophase
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Re: Need help on a new project

Post by biophase » Tue Aug 25, 2009 9:29 pm

BTW, I've noticed that dogs can already tell this when using retractable leashes. They can tell where they are very close to the end of the leash, either due to distance or tension. If you have a dog try it on your next walk.

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