what motion sensor to use

Projects General Guidance
1

Hi
I am looking for a motion sensor that is able to detect seetrough gass bubbles going up trough a plastic tube.
how and with what sensor should i do this?

2

If the gas bubbles are see-through, what is the fluid in which they travel like ?
If it is opaque, you may be able to use an LDR or similar and just look for light/dark

3

I thought about that for a while but the sensor results would be influenced by ambient light.
I was thinking of using some food coloring to color the water in the tube su the bubbles would be better visable but i dont think a light sensor would be able to detect that

4

Hi, If the ambient can not be controlled (But not sunlight??) try an IR LED transmitting through to an IR phototransistor that has a dark lens on it..

Something like (SORRY! Too long a URL..)

http://www.yourduino.com/sunshop/index.php?l=product_detail&p=208

http://www.yourduino.com/sunshop/index.php?l=product_detail&p=209

You might also try this with modulated IR signal:

http://www.yourduino.com/sunshop/index.php?l=product_detail&p=86

DISCLAIMER: Mentioned stuff from my own shop...

5

@annonymous can't you enclose the section of tube with the sensor to block ambient light?

@terryking228 I think something went wrong with your link. I've been able to prevent ambient light interference with IR sensing by using modulated IR. I remember you sell those nice modulated IR distance sensors but I don't know whether that would be useful for this application since that works on reflectance rather than transmission.