looking for a circuit

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dtghey
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looking for a circuit

Post by dtghey » Wed Jul 21, 2004 8:10 pm

I am looking for a circuit similiar to a garage door safety sensor. I am looking for a setup where I can have an adjustable beam shoot across a distance of no more than 36" and detect a break in the beam,like a pen falling off of a desk and breaking a horizontal beam. I am also looking for a latched logic transition, where a reset is required. THe key here is I need something with adjustable sensitity and range.<p>Thanks.

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Chris Smith
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Re: looking for a circuit

Post by Chris Smith » Wed Jul 21, 2004 10:12 pm

You can use many different types of light beams, lasers or leds. <p>You can couple these with coded messages or not. <p>What you need to say is what are you trying to achieve, resolution, quality, timming,...what?<p>Absolute, dont care if one gets by,..what?

cato
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Re: looking for a circuit

Post by cato » Thu Jul 22, 2004 2:06 am

Adjustable sensitivity to what? The beam you describe is either broken or it isn't. Do you want it to be broken for an adjustable period of time before something happens? Do you want something to react if the beam is only half broken?

dtghey
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Re: looking for a circuit

Post by dtghey » Thu Jul 22, 2004 4:13 am

I will try to answer both questions. First off sensitivity would be related to be able to make sure that something quickly passing through the beam would trigger it. The other is to be able to adjust the width of the beam. In other words in a garage door opener you can compromise the safety beam by stepping over it. I need a beam with a target width which is adjustable, lets say from 2 inches to 6 inches.

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sofaspud
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Re: looking for a circuit

Post by sofaspud » Thu Jul 22, 2004 12:12 pm

Mind if I ask why the target width needs to be adjustable "say from 2 to 6 inches"?
Someone here might have a way to do that. After briefly considering it, I'd say the easiest way to do it might be to have multiple beams, which could be disabled singly w/o affecting performance of the others.

dtghey
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Re: looking for a circuit

Post by dtghey » Thu Jul 22, 2004 2:29 pm

A lot of folks are more inquisitive about the specific application, than they are with providing a specific solution. I am looking to build a sensor device which will detect whan a product drops into the delivery bin of a vending machine. It cannot be infrared as the beam will be broken by a non living object. I need sensitivity adjustments because not all machines are exactly alike. Now that I have provided exactly what I want to do can anybody provide me with some assistance?

bodgy
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Re: looking for a circuit

Post by bodgy » Thu Jul 22, 2004 3:01 pm

If the objects are metal, you could use a magnetic field sensor, or a capacitance field sensor. These unless buying a ready made block unit, would probably require some experimentation.<p>So how about a weight sensor, detects when the object has fallen into the tray/bin. Unless a human hand is going to lean on the receptacle this would get around the hand in a beam problem.<p>The other way - much less work is to detect the object before it gets into the bin, in other words, just before the shoot exit either have a beam sensor which will be broken just before the object hits the bin, or it physically knocks a microswitch at the same point.<p>And the reason for being interested in the specific application is because you are more likely to get relevant suggestions rather than a whole heap of ideas, that are totally irrelevant.<p>Colin
On a clear disk you can seek forever.

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sofaspud
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Re: looking for a circuit

Post by sofaspud » Thu Jul 22, 2004 4:47 pm

Colin is exactly right. The more specific the problem is defined, the better the chance of getting a specific solution. That just makes sense. Anyway, perhaps you need a single-beam unit for one model of vending machine and a dual-beam unit for a another model. Infrared doesn't need to be ruled out - the infrared beam can be blocked by a non-living object just as well.

dtghey
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Re: looking for a circuit

Post by dtghey » Thu Jul 22, 2004 6:05 pm

Thanks for the feedback. The weight sensor requires a lot extraneous mechanical hardware. I would like to rule that out, there are some designs based upon that solution and they do not work very well, are subject to cheating.<p>I want to mount an optical unit in the case above the bin across the plane where the product would drop.<p>So does anybody have any ideas on a high level design for an optical solution?

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