Real Time Rain sensor

[roussell]

Slightly off-topic, but since were talking level sensors; I thought I'd throw this in:

http://www.maxbotix.com/

For less that $30 you get a 1" x 1" ultrasonic sensor that outputs distance from 6-254 inches with 1 inch resolution in PWM, analog voltage, or 9600 baud serial.

It isn't water proof/resistant (yet, a more resistant version is coming), so you have to take precautions to keep it dry. I use short sections of PVC pipe and open-cell foam to protect it. I'm using them to measure the draft of coal barges off the coast of Colombia and they work great.

Terry

 

[BraveSirRobbin]

Terry;

Do you use the serial option on those sensors?

 

[roussell]

Yeah, I sure do. The thing couldn't be any easier to connect; +5 Volts, ground and a serial out are all you need. Power it up and about 100 mSec later it starts sending data every 49 mSec. Feed it into Hyperterm and you'll see the copyright info and then something like - R114 - where the three digits represent the range in inches. It auto calibrates and from some crude testing (A buddy holding the sensor and the end of a tape measure and me holding the other end of the tape) the accuracy is spot on. It updates very fast too, with it sitting on my desk at work, pointing toward the ceiling (69 inches) I can move my hand up and down over it and it reacts "instantly". It’s also sensitive enough to pickup a broom handle over 6 feet away. I got mine at roboticsgroup.com for $24.95. A lot of technology for such a tiny price if you ask me…

Terry

 

[FrankMc]

Hi Terry

Nice find .....Do you think it could measure the water level inside a tank.... Im thinking you could mount it on a 6" pvc pipe stem on top of the tank this would hopefully protect it from the water and also giving a reading to the very top of the tank......

Frank

 

[BraveSirRobbin]

I'm going to get one to play around with. Good find BTW! B) Will try to get the value into a HomeSeer device via the serial port.

 

[roussell]

I was planning on using one at home to measure inside a tank as you describe. I want to start collecting rainwater and reuse it for lawn irrigation and this seemed like an easy way to measure the water level. I also want to put one on the Coi pond to add/remove water as needed.

The project at work measures the distance from the sea surface level to the top of the barge deck (draft) at one corner and sends that data to a Parallax basic stamp. The stamp uses that data along with pitch/yaw data from a dual axis accelerometer to determine the draft at the other 3 corners to calculate how deep/shallow the barge is. From that info and barge shape and size and the water’s buoyancy I calculate how much coal is in the barge. The stamp also retrieves info from a GPS and sends that along with the draft info to the control tower at the pier through a MaxStream Xtend 900MHz serial radio. The whole thing runs off solar/battery power.

I found similar industrial sensors for $500-$600 each. I figured at that price, I could make the Maxbotix ones “disposableâ€, replace them more often and still come out better in the end.

I attached a drawing of the sensors water resistant enclosure. It looks way more advanced than it is. The parts consist of a PVC 1-1/2†--> ¾†NPT adapter and a PVC 2†--> PVC 1-1/2†both from the plumbing section at your friendly neighborhood Lowe’s or Home Depot. The foam is just some ¾†grey packing foam that came in the Maxstream radio box. I noticed that the ultrasonic waves would pass through it with no degradation in distance measurement so I cut a piece to fit the 2†opening of the housing. The data cable is a LAN patch cable that passes through the center of the ¾†threaded section of the housing. The idea being that the sensor housing will screw onto a piece of ¾†conduit and the cable will be inside the conduit… It works well and is effective in keeping the sea water from reaching the sensor at normal barge speeds (~3 knots).

 

[roussell]

A couple of pics of the housing...

 

[roussell]

Another

 

[roussell]

Last one...

 

[FrankMc]

Thanks Terry for the info ....Im going to order a couple of these......

Frank

 

[elcano]

One thing i wasnt sure of was , what happens with the tubing....?? Is it suppose to be installed vertically or horizonal ?? ..didnt grasp that part...??

The tubing is installed anyway as long as the other end is in open air to get a reference of the atmospheric pressure. This sensor is a differential pressure sensor and works by comparing the pressure difference between your atmosphere and the bottom of you water tank. This pressure diference will depend on the height of the water above the sensor (not the width of the tank).

So it does not matter how you install the tubing. You just need to make sure that the sensor get the correct pressure values at both sides of the pressure sensor.

 

[elcano]

I know I mentioned Eric's (Hobby Boards) Moisture Sensor above, but just now noticed that it has a solder mask to keep oxidation down (I know this was Elcano's concern). So I'm wondering if you use this do you still need to use a "pulse" method or just look at "raw" resistance via a biased circuit??

After reading a little more aroung internet, they said that waht they want to prevent is 'plating'. I assume that they meand the accumulation of free ions in one of the poles (cathode or anode). To prevent oxidation the most expensive ones use gold grids. However they still seem to use the ac signal.

 

[elcano]

I also enquired if it was possible to use this chip for moisture sensing....the guy i spoke wasnt a technical guy but indicated it may be possible.....

Do you mean ambient humidity (sorry I got lost in translation)?

This chip is just an oscilator combined with a conductivity sensor. They water sensing element is the grid (BSR's post above). I'm not sure if the grid is going to work for you. I would expect the grid not to conduct practically anything (near zero conductivity) until a drop of water closes the circuit, even at 90% non-condensing.

If your goal is measuring soil moisture, I think that if you connect some of the other gypsum moisture sensing elements for simulating soil moisture it should work. However, in this case I'm not even sure if you need it. The contacts on the gypsum sensor are separated by a lot of gypsum and probably the ions cannot glow from on pole to the other, thus preventing the plating. Probably a DC biasing signal is enough.

 

[ericvic]

Elcano,

You absolutely can't use DC with the gypsum soil sensor. If they are moist and you use a DC ohm meter to meaasure the resistance you will ruin the sensor. It only takes a few seconds to start the "plating" and then the sensor will never read quite right again. Believe me, I say this from experience

 

[elcano]

Thanks Eric. You learn something everyday.

Here is another option:
http://www.rbeelectronics.com/fld698.htm

Here is the response that I got to an inquiry:

Hi Eric, The most common level detector we sell is our LD698 which sells for $25.97. This is a 12 VDC model. We do not have any distributors and just sell direct from our factory. If you have any other questions, please let us know. Best regards, Steve Wolff RBE Electronics, Inc. 800-541-4056

This is a very rugged device that seems to be suitable for outdoor usage. The probe can even be connected up to 25 ft away.