Hello,
I am designing an installation where ice (with a LED inside) is suspended a few feet above a bowl with water in it and is melting. what I am trying to do is pulse that LED whenever a drop of water falls from the ice and lands into the water... (whenever the drop hits the water)
What would be the best method/sensor to do this?
I was looking into sound sensors, weight sensors or even motion sensors?
What do you think?? and is there anything specific you can recommend?
Thanks!
Sound could work with the right sensor and little background noise.
Or maybe reflected light from the water surface - there are various IR sensors that
measure that, a ripple ought to change the reading for a short while?
What about a light barrier?
Here's a modified scheme from an X-ray diffraction system I designed years ago. Use a photo diode and an LED of the dome shaped version. Collimate both using long tubes like soda straws or a pin hole scheme. Aim the source at the point on the liquid surface where the drop will fall and at the shallowest angle possible. Locate the receiver at the opposite side and aiming at the same point. When the surface is calm, the beam will be reflected and when disturbed, the intensity will drop for a short time. It's just a matter of setting a threshold level and accounting for a ripple effect similar to switch bounce.
I will vote for the microphone detection method.
After 70+years with high frequency hearing loss, I finally got in-the-ear hearing aids. They limit the LF sound and amplify the sound above 1500HZ. Water droplets into a bowl make lots of sound! You need to amplify and filter the sound to get just the HF to trigger the LED.
Paul
The OP could get the Teensy 3.2 and the audio adapter from PJRC and use the FFT function to identify the frequency nature of the collision. Thereafter, use that same setup with continuous FFT analysis and trigger on the presence of the unique sound.
How about this: Excuse the sloppy drawing, I'm old & shaky >:(
pylon:
What about a light barrier?
could you elaborate, im not sure what you mean
MarkT:
Sound could work with the right sensor and little background noise.Or maybe reflected light from the water surface - there are various IR sensors that
measure that, a ripple ought to change the reading for a short while?
would an IR reflective sensor work? or perhaps a light dependant resistor?
mbartolucci:
could you elaborate, im not sure what you mean
You probably now where exactly the drop will fall. Install a light barrier on that path down to the water. It must have a narrow beam, best is probably a laser beam (these are quite cheap these days). Although the drop is transparent it will distort the light enough to be detected.
As the ice cube melts, the location of the drips might change, so a "light barrier" (aka "electric eye") with a very narrow beam might not work all the time. Dunno - never watched an ice cube drip! Probably depends on initial cube orientation, air drafts, or....
Also, the OP needs to think about how to detect two more more drips falling in quick succession (assuming that is something that is desired). A microphone or a properly positioned electric eye could probably do that, but I'm not sure about the diffraction/wave/ripple detection system.
Maybe you can attach the ice to a precise scale and detect the weight change?