Trigger level of water in a small glass tube

Using Arduino Sensors
1

Hi Everyone,
I am pretty new to arduino, sensors and even basic electronics so, please, forgive any excessive naivety.

For my project I would need to trigger a countdown when water in a glass tube (around 0.5 cm diameter) rises up to a specific level (or falls down). This trigger should react quite promptly (milliseconds response would be ideal)
Do you think that this photo interrupter sensor could be used?
http://www.cooking-hacks.com/index.php/photo-interrupter-os25b10.html
I suppose that the tube full of water should have a stronger absorbance in the IR region than when empty.

My doubts are:

  1. The difference in light intensity would be to small to be detected reliably?
  2. Would the glass have a too strong absorbance so that no meaningful detection can be performed?

Any suggestion for alternative sensors?

Thank you in advance.

Renato_

2

How about one of these?

3

No, it wouldn't work. That is a sensor for moisture content in soil. I need to "see" when the water rises in a tube...

4

Well dry air is the same as dry soil, and wet soil is water. So you just dangle that thing in the tube so the points are at the right level.

But if you Google water level sensor or similar, you'll find dozens of answers..... but they tend not to be optical, more to do with conducting.

Does the water have to be clear?- if you dyed it, then it would be opaque and a visual spectrum photo thingy would work?

5

I am sorry, I didn't specified that the sensor cannot touch the water. It must be outside of the glass tube and I cannot modify the glass tube in any way. I cannot change the water sample ether.
I am trying to build an automatic Ostwald viscometer (Viscometer - Wikipedia). Therefore I need a way of "seeing" when the water reaches the mark on the glass tube.

6

Would this type of Proximity Sensor https://www.sparkfun.com/products/246 work for you? I don't know if the water is opaque enough for it to sense it, but it is cheap enough to give it a try.

Best of luck!

7

I am sure you can do it optically. A tube with water in it, is not the same as a tube without water.
It might be fiddly and you might need to control the illumination in the area where you are doing
the detecting and then calibrate it carefully.

If you are going to try using some kind of led on one side and some kind of photodetector on the
other side, you could experiment with placing these obliquely, in order to detect the change
in effective refractive index when the water reaches the level of the detector.

8

I will try with a photoresistor, and a led, then.

Thank you all for the advices.

Renato_

9

I would suggest a hall effect sensor. Place a rare earth magnet inside the tube in something that floats, cork or whatever, and mount
a hall effect sensor on the outside of the tube. Put one hall effect up top and one on bottom. I've thought about doing something similar
to your project to monitor fluid levels in tanks. I can't think of a more economic or easier way.