Can anyone recommend a good range finder under $50 that has resolution of around 1mm or even 5mm. The ultrasonic range finders I've found are, at best, 30mm. Does IR work for liquid? I'm trying to be able to measure the amount of liquid without rigging anything to the container (i.e. no sensors in the liquid itself).
Thanks!
you might be able to integrate multiple readings to increase the resolution.
Or you can improve the reading of the sensor, checkout the work of Tim here - http://arduino.cc/forum/index.php/topic,106043.0.html -
Do the math of what is feasable.
Speed of IR beam times shortest time to measure times 2 = minimal distance to measure (probably times 2 again due to noise)
(OK you say it uses doppler => the math gets a bit more complex 
Thanks! This is great. Now, back to my old dusty physics books. 
Speed of IR beam times shortest time to measure times 2
Don't even think about starting to measure flight time of an IR beam using an Arduino.
OP, what sort of distance do you need to measure levels?
Could you weigh the recepticle?
Don't even think about starting to measure flight time of an IR beam using an Arduino.
in 1 uSec an IR beam goes only 300 meters about what sounds does in 1 second.
but after 300 meter the light will be diverged too much, maybe IR laser could be done?
in 1 uSec an IR beam goes only 300 meters about what sounds does in 1 second.
I don't see where this one is going. There is absolutely no way an arduino is going measure time of flight of a light beam to one or five millimeter accuracy.
Weighing the receptacle might be the best choice, actually. I was never thinking about measuring the timing of IR, but measuring the timing of the ultrasonic ping multiple times is a good option also.
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in 1 uSec an IR beam goes only 300 meters about what sounds does in 1 second.
I don't see where this one is going. There is absolutely no way an arduino is going measure time of flight of a light beam to one or five millimeter accuracy.
N0where, I was just thinking out loud.
http://www.maxbotix.com/products/HRLV.htm
Maxbotix claims this sensor has a resolution of 1mm. But take that with a grain of salt. Unless you're in a perfect environment like a sound proof lab like they are.
jonlucc:
Can anyone recommend a good range finder under $50 that has resolution of around 1mm or even 5mm. The ultrasonic range finders I've found are, at best, 30mm. Does IR work for liquid? I'm trying to be able to measure the amount of liquid without rigging anything to the container (i.e. no sensors in the liquid itself).
Thanks!
All the ultrasonic sensors I've used are accurate to about 5mm. Typically, if you're getting bad results it's because of the library or because you're not factoring the air temperature when calculating distance. I created a NewPing library that's much more accurate, faster, and smaller than other ping/ultrasonic libraries. If you also have a temperature sensor, I can set you up with a simple function to give accurate results.
The NewPing library can be found here.
Tim