Screndib

Alright, I've got a 2'x2' square "tub" with a couple inches of water in it. I'm looking for a way to detect when and where an object (such as a person's finger) penetrates the surface of the water.

So far I've thought of an array of infrared beams positioned on two sides of the tub with detectors on the other two sides (example below). The whole system would be slightly above the water. Each beam/detector combination is spaced approximately a centimeter apart so that it's near impossible to put something in between them. At this point it becomes a simple matter to determine the position from the broken beams.

Now first, is there a cheap infrared LED that is able to throw a focused beam of light 2-3 feet, or would I need to move to something like an IR laser (which from what I can tell, making an array of them would be cost prohibitive). Perhaps even a packaged array set up already?

Second, is there simply a better way to go about doing the whole thing?

Now this the first time I've ventured into anything like this, so any and all reccommendations or ideas would be great to hear.

Attached Images

ir_153.jpg (31.6 KB, 287 views)

stevez

I have little experience with LED/sensor combinations but it seems to me that if you placed light sources opposite sensors - and scanned them at the same time then there would be less need for focus, possibly allowing you to use low cost LEDs and sensors. You might also reduce the blind spots by scanning pairs that are not quite opposite each other.

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stevez

jrz126

what about a motion sensor from like a sensor light or something. if you mount it in a corner, it might be able to work. I dont know how well it would work sensing in water though

__________________
Jeff Zimmerman
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

Screndib

Do you mean turn on each LED in sequence instead of having them all on all the time?


Would a motion sensor be able to tell me where the "plane" was broken?

jrz126

how far is the object going to penetrate the water? is it just going to break the surface?

__________________
Jeff Zimmerman
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

stevez

What I was thinking was turn on an LED/sensor pair at the same time so that the position of the source is known - that might relieve you of some worries about beam width.

In the simplest arrangement you might think in terms of X and Y coordinates where the LEDs would be lined up exactly opposite the sensors. Maybe you'd have a 10 by 10 array - 10 LED/sensors for the X axis and 10 for the Y axis. A beam interruption on either axis would give you the position more or less directly.

You might find that some kind of diagonal pairing or multi-LED/single sensor (or the opposite) would increase the coverage. An example- if something small enough was in between pair X4 and X5 it might not be seen by either pair but if LEDX4 were scanned with SensorX5 it might see it. This is likely to be more of a software issue than a hardware issue.

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stevez

stevez

What I was thinking was turn on an LED/sensor pair at the same time so that the position of the source is known - that might relieve you of some worries about beam width.

In the simplest arrangement you might think in terms of X and Y coordinates where the LEDs would be lined up exactly opposite the sensors. Maybe you'd have a 10 by 10 array - 10 LED/sensors for the X axis and 10 for the Y axis. A beam interruption on either axis would give you the position more or less directly.

You might find that some kind of diagonal pairing or multi-LED/single sensor (or the opposite) would increase the coverage. An example- if something small enough was in between pair X4 and X5 it might not be seen by either pair but if LEDX4 were scanned with SensorX5 it might see it. This is likely to be more of a software issue than a hardware issue.

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stevez

zachtheterrible

As long as its just going to be someone putting their finger in the water, creating small ripples, maybe you could get some kind of sensor that senses the ripple in the water. mount 4 of these on the sides of the tub. Then feed the sensors into something that will calculate the position depending on when each sensor is activated.

I know this is quite complicated, but it would be prety precise :lol:

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I'm no electronics god, i just talk too much.

Screndib

The water ripples idea would be pretty cool. It sounds like it would end up being a nightmare though with multiple ripples going everywhere.

And also, it doesn't matter how far it penetrates the surface, I'm just looking to tell when it does penetrate the surface.

Your idea stevez might work, I think this is something where I'm going to have to just grab some parts and mess around.


On a side note, can anyone give me any other reccommendations on where to find cheap parts? So far I know of Jameco, Digikey, and Mouser.

plot

I prefer the ones you just listed becuase i've used them and had no problems with them. Newark.com is another very good professional reliable source for parts.


Other sites i've used with no problems:
www.allelectronics.com (surpluss store, less stuff, better prices)
www.lsdiodes.com (for LEDs)
www.hobbytron.net (more for kits then anything)


other sites that i havn't personally used but know many people who have and recommend them:
www.eem.com
www.meci.com
www.mpja.com
www.partsexpress.com
www.eled.com (for LEDs)
http://www.alliedelec.com/ (direct supplier)
http://www.apexjr.com (power and audio related stuff)
http://www.herbach.com/
http://www.futurlec.com/Components.shtml (delivers ANYWHERE in the world)

more sites someone else i know has used for miscelaneous electronics stuff...
http://www.aicmicro.com/
http://www.bgmicro.com/
http://www.circuitspecialists.com/
http://www.etronics.com/
http://www.meniscusaudio.com audio stuff
http://www.ramelectronics.net/