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computer guy
01-11-2008, 05:03 PM
I need to measure the level of rain.
I have designed this circuit however since I am still learning some of the basic electronic laws I do not know if it will work.
Could someone please take a look and tell me if it will work.

Thank you http://forums.parallax.com/images/smilies/smile.gif

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Post Edited (computer guy) : 1/11/2008 9:17:37 AM GMT

bambino
01-11-2008, 06:23 PM
I guess thats doable. Have a look at the basic stamp Applied Sensors Text!

computer guy
01-11-2008, 06:47 PM
I am assuming that the BC847B transistor will work, it is rated at (5v 20ma).
The example in "Applied sensors" is a bit overboard for my liking. I am also limited to a fairly small space and 4(555 timers) will take up a lot of room.

Thank you http://forums.parallax.com/images/smilies/smile.gif

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Post Edited (computer guy) : 1/11/2008 10:57:53 AM GMT

OzStamp
01-11-2008, 07:04 PM
In the real industrial world .. a low ac volts is used between sense and common probe..for obvious reasons.
Some use Earth as the return .. low current ..

Google it and you will find out why...
Clue .. it has something to do with electr....

But there is nothing wrong with your principle.. like the drawing Anthony..

cheers
Ron Mel oz

computer guy
01-11-2008, 07:18 PM
Thank you, I did the entire drawing in Eagle.
Couldn't find anything with google.
Ron, would you be interested in purchasing something from me for a change - http://forums.parallax.com/showthread.php?p=698795 http://forums.parallax.com/images/smilies/smile.gif
You could put them in with your orders, as a gift to your customers. Just a thought. http://forums.parallax.com/images/smilies/idea.gif

Than you http://forums.parallax.com/images/smilies/smile.gif

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Wolftec
01-11-2008, 07:35 PM
Most commercial rain metters i know have a tilt recipient.

Once the water reach a specific weight it tilts to dump the water out and as it does it presses a switch. Timimg between 2 impulses will give you the downpour rate.

In your case you have to make a hole on the contanier, and calibrate it to a specific mesure, that may prove trick. hole too small, and it will top up very quickly, hole to big and it won't give a precise measure.

computer guy
01-11-2008, 07:55 PM
Wolftec,
What do you mean by hole? The only hole in my design is at the top of the gauge and that is to let water in.

Thank you http://forums.parallax.com/images/smilies/smile.gif

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Check out my robot using the propeller RECONAUTOR (http://robot.tmcp.com.au)

Joerg
01-11-2008, 08:04 PM
Hi
with a lot of experience in the field of ambient measuring systems i see two critical points in your design:

- DIRT! since water tends extremely to accumulate this stuff your contacts will not work for a long time, until you clean the contacts often.

- and how do you empty the container? Normally this kind of systems are working continuously, so you will need to poor the water every now and then.

By the way: the standard area (EU) for a rain gauge is 200mm2

and a second hint: If using EAGLE (like i do since over 15 years) for creating bitmaps you may use the .PNG format which makes the files much smaller!

Saluti Joerg

computer guy
01-11-2008, 08:20 PM
The picture is more of an electrical representation than mechanical.
Some form of valve will probably be added to empty water.

As for dirt, due to the size of the contacts I figured dirt would not be a problem.

Thank you for the advice with Eagle, will export as PNG next time. http://forums.parallax.com/images/smilies/smile.gif

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steve_b
01-11-2008, 09:31 PM
I think you could have some oxidation problems with your set up. Hard to say....but I'm sure it'd eventually become intermittant.
You could go optical, have some lasers/leds on one side shining at a photocell on the otherside. I assume water would refract enough of the light that when it covered that portion of the sensor it would block it.
Float bulbs could work similar.

We use tipping buckets. Basically a "catch" at the top drops to a funnel that restricts the flow enough so that the 'force' of the water doesn't falsely tip the "bucket".
The "bucket" is basically a couple of small "buckets" on a see-saw. There are some set screws to adjust just how much water it takes to tilt the see-saw. We typically set it for 0.2mm of rain. As the bucket tips, there's an arm with a magnet on it that triggers a mercury switch (we use mercury to prevent bouncing contacts; could easily use a reed switch).
The nice thing about tipping bucket types, is that you can determine rain rate by the number of tips in a given timeframe.

The other style of precip measurement we use is a weighing gauge. Some are encoder read (a scale system pulls an arm connected to an encoder, the heavier it gets, the higher the encoder goes) and others are hanging wire types (a vibrating wire; as the bucket gets heavier, the frequency of the wire goes up -- think playing a guitar...tighten the string and it's pitch/freq goes up).

Hope that helps!

Cheers

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<FONT>Steve



What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!

Beau Schwabe
01-12-2008, 12:39 AM
computer guy,

There might be easier ways to sense the level of water where you would not need to worry about contact oxidation or impurities left on the electrodes through evaporation. Not to mention electrolysis effects with electrodes directly in contact with your fluid.



check this link...

http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol1/col/nv27.pdf

If you are using a Propeller, it could even be easier than the link mentioned above (<- read CD4060 IC not even required)· ... If I get a chance this weekend I will test this.








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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 1/11/2008 4:54:30 PM GMT

Philldapill
01-12-2008, 09:50 AM
Like other guys have said, I bet oxidation will be a problem with your contacts since you have a small current flowing. To minimize the current, I'd suggest using mosfets instead of bipolar transistors. They pull VERY little current and are effected more by voltage than current like bipolars.

deSilva
01-12-2008, 10:33 AM
Seems the original intention got lost a little bit. Rain in fact can be diffucult. "Typical" water has a conductivity between 100 µS/cm to 1000 µS/cm. Assuming we have 1 cm2/cm somehow this means 1k to 10k Ohms. This is nothing very special as far as current goes. (And is the reason why you should not use electrical equipment in the bath tube....) Base current will be ample 1 mA, as far es the water is concerned. It could even be useful to add a 100k current limiting resistor to delay the unavoidable electrochemical effects.

But as mentioned many times here, you HAVE to use AC for a more professional usage - and best platinum electrodes as well http://forums.parallax.com/images/smilies/smile.gif

Post Edited (deSilva) : 1/12/2008 2:58:59 AM GMT

OakGraphics
01-13-2008, 04:56 AM
steve_b said...
We use tipping buckets. Basically a "catch" at the top drops to a funnel that restricts the flow enough so that the 'force' of the water doesn't falsely tip the "bucket".
The "bucket" is basically a couple of small "buckets" on a see-saw. There are some set screws to adjust just how much water it takes to tilt the see-saw. We typically set it for 0.2mm of rain. As the bucket tips, there's an arm with a magnet on it that triggers a mercury switch (we use mercury to prevent bouncing contacts; could easily use a reed switch).
The nice thing about tipping bucket types, is that you can determine rain rate by the number of tips in a given timeframe.
This piqued my curious nature - so I found a link that demonstrates what you are talking about, just a bit differently.
http://www.weathershack.com/education/tipping-bucket-rain-gauge.html·http://forums.parallax.com/images/smilies/tongue.gif

Tracy Allen
01-13-2008, 06:39 AM
Quantum Research (http://www.qprox.com/) makes capacitive "key detection" chips that might be useful for your project. I have a QT114 controlling the sump pump in my basement and have used it for several work related projects. It detects two discrete levels, and is meant specifically for water or powder level detection. I see it has been discontinued, but they are still around. The QT110 series (one of which is carried by the Parallax store) detects one key (or water level) on a non contact basis. I have also a few QT117 chips, which were analog level detectors with a 16 bit digital output, in an 8-pin package, but those don't come up at all now in a search.

Quantum now seems to focus on the multi-key decoders, but I see no reason why they could not be used for detection of multiple levels on a non-contact basis. When you look at the description of those chips, you will see that they talk a lot about rejection of signals from water films. Films are in fact the bane of capacitance based water level sensors. It might work fine at first, but after a while a thin layer of crud (salt, minerals, dirt, algae) builds up on the detection surface. That forms a conductive path that extends considerably above the level of the water that you want to measure , or onto a neighboring key if it is a keypad. The effect of that film can vary with temperature and humidity and with the passage of time. One solution to that problem is to operate the detection electronics at a very high frequency or with very short pulses. The distributed thin film acts kind of like a distributed network of Rs and Cs, and it cannot respond as fast as the main element. Those distributed Rs and Cs act kind of like "soakage" in a capacitor. System identification requires separating the fast responding from the slow responding elements. The nice thing about the capacitance methods is that they do avoid the corrosion issues and the miniature batteries that are formed in corrosion layers.

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Tracy Allen
www.emesystems.com (http://www.emesystems.com)

computer guy
01-13-2008, 06:53 AM
After researching the tipping bucket idea, I have decided that it is the best approach for my project.
Just one question, after looking at this link (http://www.weathershack.com/rainwise/rainew-rain-gauge.html) I am a little confused how you are supposed to get the water into the bucket.

Could someone please explain this. (steve_b)

A side on diagram of the whole assembly might help.

Thank you http://forums.parallax.com/images/smilies/smile.gif

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Post Edited (computer guy) : 1/12/2008 11:07:33 PM GMT

Tracy Allen
01-13-2008, 07:54 AM
Rain falls into the bucket out of the sky! There is a funnel inside that directs it into the tipping mechanism. Is that the question?

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Tracy Allen
www.emesystems.com (http://www.emesystems.com)

Post Edited (Tracy Allen) : 1/13/2008 12:04:29 AM GMT

computer guy
01-13-2008, 08:20 AM
Yes that was the question.
Your Diagram also answered my next question, obviously the buckets alternate and the reed switch detects the change over.

This should be fun (Hardware shop visit).

Now that I know how they work I might just buy a rain gauge and interface it with the propeller (like a normal switch I presume, 10k pullup).

Thank you http://forums.parallax.com/images/smilies/smile.gif

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deSilva
01-13-2008, 08:37 AM
The picture on their site is even more instructive...

computer guy
01-13-2008, 09:00 AM
That picture makes more sense after seeing Tracy Allen's diagram for some reason.

Thank you http://forums.parallax.com/images/smilies/smile.gif

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Check out my robot using the propeller RECONAUTOR (http://robot.tmcp.com.au)
If you like my avatar then check this out Propeller Domed Sticker (http://forums.parallax.com/showthread.php?p=701193)

Post Edited (computer guy) : 1/13/2008 2:24:56 AM GMT