PIR Sensor in Water(?)

mollensoft

Anyone know for sure if the PIR sensor will detect IR Changes in Water? I want to detect the movement of fish in a rather large aquarium and was thinking the PIR sensor might be able to detect fish swimming by (despite their cold blooded nature). I am planning to mount the sensor very close to the water's surface but am uncertain if this sensor would sense anything below the water surface.

Thanks for any advice..

-BigAL

Chris Savage

Hello,

The PIR Sensor detects rapid heat changes within its field of view. As fish are cold-blooded they will not create a heat differential that will be detected by the PIR, especially under water. You might try just an IR LED and Detector to detect momentary loss of signal.· Take care.

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Chris Savage
Parallax Tech Support

mollensoft

Ok... Thanks for the advices, I do appreciate it :>)

Mightor

Mollensoft,

You could try keeping a small whale or dolphin in your aquarium to see if that works with your PIR sensor. They're warm blooded.

All that aside, there's a good chance a LOT of the light will be deflected and refracted off the surface of the water. Most aquariums have a pump that intentionally breaks the water's surface to prevent a build up of that oily residue and aerate the water for the fish and bacteria. Your best bet is to put the sensor and LED on each side of the aquarium. This may not be what you need though.

If you want to detect movement, why not set up a grid like this:

   +--------------------------------+
L  |                                | S  
S  |                                | L
L  |                                | S
S  |                                | L
   +--------------------------------+

Where L is a LED and S is a sensor. Make sure you cycle the LEDs and only active the sensor that corresponds to the correct LED. You can go real fancy and have an array on the other sides too. That would allow you to quite accurately determine position. Also keep in mind that the light may be diffused a LOT in your aquarium, depending on current, purity, air bubbles, etc, etc.

I am not an expert on fish-vision but make sure that a 38KHz (or thereabouts) modulated signal doesn't mess with their puny little brains. We've all seen what human science can do with sharks in Deep Blue Sea. Last thing we need is a super intelligent guppy ramming its way out of your aquarium.


An example of a BasicStamp2 powered guppy

Gr,
Mightor

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| What the world needs is more geniuses with humility, there are so few of us left.

Post Edited (Mightor) : 7/29/2007 6:01:05 AM GMT

Bruce Bates

Mollensoft -

Are you just trying to sense activity at one specific spot near the front of the tank? If so, I might have a different approach for you.

Regards,

Bruce Bates

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LilDi

Just a quick note about PIR detectors. Since PIR devices sense thermal infrared, I'm pretty sure the water will absorb most if not all of the thermal infrared energy and render the PIR useless, even with a whale in the tank.

Mightor

LILDI said...
Just a quick note about PIR detectors. Since PIR devices sense thermal infrared, I'm pretty sure the water will absorb most if not all of the thermal infrared energy and render the PIR useless, even with a whale in the tank.

I'd like to test this. I have quite a few aquariums (one is even 360L - that's 95 gallons for the metric-impaired), if someone can supply a small, say 50cm (20") long, blue whale and a PIR sensor, we can check the validity of your claim.

Gr,
Mightor

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| What the world needs is more geniuses with humility, there are so few of us left.

Steph Lindsay

Have you ever heard of the artist·Ken Rinaldo and his "Augmented Fish Reality" ? It is a rolling platform with a donut-shaped fishbowl with 4 IR sensors spaced around it.· When the Siamese fighting fish inside moves close to a sensor, the·platform moves in that direction.··We had one in our·office lobby - it was BASIC Stamp controlled.· The ones at the website below·are part of a more elaborate art installation, and include cameras·that project what's going·on in the bowl onto the back wall.

http://www.kenrinaldo.com/

His website menu system is a little different, this is how it worked on my computer:·Hover your mouse over the top-left pixel-flower until you see "art" and then choose the second single-square stem from the left for Augmented Fish Reality.

-Stephanie Lindsay

Mightor

His robots look almost look like they're from some kind of sci-fi movie. The website sure is different, though. Was the fish ting one of these: http://www.ylem.org/artists/krinaldo/works/augmented/ar3.html ?

Gr,
Mightor

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| What the world needs is more geniuses with humility, there are so few of us left.
| "Wait...if that was a compliment, why is my fist of death tingling?"
| - Alice from Dilbert

Steph Lindsay

Yes, that is Ken Rinaldo's work. I kind of think of them as land exploratory vehicles for fish, a reverse submarine. Maybe a supermarine.