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Subject: Re: Water sensor
Date: Fri, 10 Jan 2003 13:42:28 +0000
NNTP-Posting-Date: Fri, 10 Jan 2003 13:42:38 +0000 (UTC)
X-Newsreader: Groupwise 6.0.1
>That's the one, although I was also thinking of converting this for
>application that involved sensing various smallish water volumes simply,
>the positioning of point sensors at appropriate graduated levels up the
>side of a pipe or vessel.
You can sense multiple levels by having the probe that generates the signal
at the lowest point, and multiple sensing probes at higher levels up the
>I'm not sure of the exact conductivity of water, particularly that
>resulting from air-con semi-distillation, but I'd imagine it wouldn't
>be very high. I can imagine a system like this being prone to picking
>up stray signal from the other probe's feed wire. Ideally I'd like the
>probes to be as simple as possible and on the end of relatively long
Water from air con condensate will conduct You may need an op amp to amplify
the signal a bit from the sensing probe, but it does work with air con
condensate (trust me on this, i've done it).
You can make it quite noise immune for long cables as well cos you know the
frequency of the signal you are looking for (you'd be generating the ac
signal injected into one of the probes), so you can filter out all other
>This seems a very elegant solution apart from the small difficulty of
>obtaining known-impedance wire lengths that contain uninsulated but
>separated conductors without having to butcher something yourself, and
>figure out impedance afterwards.
>However, I think that the electronics required to implement something like
>this lie a little beyond the simple input stage to microcontroller that
>I had envisioned for this project.
hehe, yeah, its a bit beyond my capabilities thats for sure, but i'm pretty
sure it would work.
>Was there a fourth option? :)
hmm, there is a company that sells a device that was designed for those taps
in washrooms that you just touch for them to come on. Trouble is i can't
remember their name, but they'd adapted it for use as a touch switch sensor.
I think it was capacitive based sensing. they had an apps note for sensing
water level / presence.
We did have a part for playing with, but didn't have a great deal of success
the ac signal and sensing probe method i described above works reliably and
can be made very cheap.
if you email my home address (firstname.lastname@example.org) i may be able to
help you a bit more.
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