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The HC-SR04 is directly connected to an Arduino board with the receiver end(echo) connected to analog pin 2 and the transmitter (trigger) connected to digital pin 4.

I am wondering if I can use the sensor to sense the change in saturation from when object block its path. The receiver and transmitter will be positioned like this

enter image description here

The line in the middle is supposed to be a paper. I'll be using it to see the difference between one paper and two paper when they travel trough the two.

Now I'm not sure if this is possible but the way I see it working is kind of similar to an IR LED Arduino program connected to an LED, where when one paper passes trough the light gets a little bit weaker and with two it takes a heavier hit.

Is this possible?

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  • $\begingroup$ Hi hollander - if you want to draw a diagram and upload it to a site like imgur.com, I can edit the question to use that image instead of your ascii art diagram. Would that be more helpful? $\endgroup$ – Ian Oct 17 '13 at 5:07
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The short answer is "no, a sonic range sensor can't do it".

It might "work" under very controlled conditions, but relying on only the attenuation of the returned signal to determine thickness may leave you open to incorrect results due to multipath propagation effects.

The more traditional way to measure thickness with sound is called profiling. The following is excerpted from a USGS Woods Hole Science Center page on Seismic Profiling systems:

reflection profiling is accomplished by [emitting] acoustic energy in timed intervals [...]. The transmitted acoustic energy is reflected from boundaries between various layers with different acoustic impedances [i.e. the air and the paper]. Acoustic impedance is defined by the bulk density of the medium times the velocity of the sound within that medium. The reflected acoustic signal is received [by one or more microphones]. The receiver converts the reflected signal to an analog signal [which is digitized and heavily processed to determine the makeup of the materials].

Seismic Profiling System

Rather than just measuring the time of the incoming pulse, you'd need to analyze both the time and frequency domain of the recovered signal to solve for the acoustic properties necessary to transform your transmitted pulse into the received pulse.

So the long answer is that it can be done sonically, although a sonic range sensor is generally insufficient for this purpose.

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