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How to detect a squirt from a water pistol

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SABorn

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Hi all,

Based on a project i am helping someone with, we need to detect a squirt of water onto a target from a water pistol.

Sounds simple, but all ideas so far have problems with them.

The detection of water on the target will be done with a micro processor, so this allows for many theorys of applications.

Any ideas????

Pete.
 
Why not just a simple conductivity sensor - sense the current flowing between the tracks on a pcbwhich is the sensor? Just to stop the water staying on the detection electrodes (i.e. copper strips on a pcb), use a decent voltage & power through them to evaporate the water (tin the electrodes so they don't self destruct).
 
How powerful is the stream? I've never tried this before, but I understand a piezo can detect when an object stirkes a target.
 
I had thought of the pcb tracks but there is too many problems with his i think.

Now..Brownout, might be on target here (punt intended) a piezo could well work fine, if i can keep he water out. ( you know i knew that but just didnt think of using it ...dohl)

Thanks guys.........any more suggestions.

Pete.
 
hi,
What are the restrictions on the construction of the 'face' of the target.?
 
If you only care about the water striking the target and not where it strikes then I like BrownOut's suggestion. I have applications where I use an accelerometer to detect a bang. With proper amplification and the right choice of accelerometer they can be really sensitive.

Ron
 
what if you were to take two layers of copper screen (like what you'd find in a screen door, I know my LHS sells this stuff by the roll), frame it however you desire but essentally it would be one layer right behind the other layer, with a small air-gap between them (space them and isolate them so they do not contact eachother). One screen would be positive the other layer to ground. When a squirt of water is directed at the target it would pass through the first layer and into the second layer. Because it's a screen and not solid the stream should remain fluid long enough to short the two layers momentaily.
The nice thing is once the forward inertia of the water has dissapated the steam will be broken and the two layers will not conduct regarless of if there's residual moisture on it or not.

You could run the leads to an analog input pin of a IC or to a transistor to drive an led or relay or whatever...
 
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Some good ideas guys.

The mesh screen idea was something i had considered, but felt it had drawbacks and there had to be a better way.

I am told the target area is about 2 inch diameter so think a piezo should work ok.

An accelerometer is a good idea too but think the cost might be a bit high for the limited budget allowed.

What are the restrictions on the construction of the 'face' of the target.?

None really, except to be waterproof, Im thinking a flexable plastic sheet front panel with piezo sensor mounted behind it.
Any thoughts Eric?

Pete.
 
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None really, except to be waterproof, Im thinking a flexable plastic sheet front panel with pieze sensor mounted behind it.
Any thoughts Eric?

Pete.

hi,
I was thinking about a membrane under tension, bit like a 'drum' skin.
Glue a low cost miniature microphone/s to the inside surface, followed by a OPA and filter.
 
Hi Eric,

That would be another option.

Wouldnt a piezo attached to the drum work the same, as i have seen designs where the piezo is attached to a window glass and used as a listening device, the glass transfers the sound vibrations to the piezo.

I did do a few bench tests with a piezo from a Xmas card and fed it through an opamp and then used a cap between the first and second stage to create a extended time pulse, so there was time for the micro to detect the hit.

I think it should work but might be subject to temperature shifts and other interference.

I will board up a prototype and see how it goes.

Pete.
 
hi,
A piezo [or an old record player piezoelectric cartridge/needle holder] gives a fair signal when tapped.
 
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