I have pack of paper and would like to count how many peace of paper i have using infrared or any invisible beam. If I am able to measure the attenuation of the beam I will be able to deduce the number of papers.
What small IR for Arduino is suitable?
IR sensors work by measuring the level of IR light reflected off of a surface. Whether you're using one piece of paper, or a thousand, the sensor can only detect the presence of something in front of it. It can tell you the distance to the first page, but cannot measure its thickness.
oh, ok so i'm trying to use the wrong tools. Thanks
Some IR wavelengths will penetrate paper, which is predominately cellulose fibers, but the penetration depth at even the optimum wavelengths is quite small, likely on the order of microns, not millimeters. Keep in mind that infrared light is a region of the electromagnetic spectrum, with wavelength from 0.7 to 40 microns. Another aspect of the problem is that IR light can be reflected and transmitted, so the amount of light penetrating depends critically on the characteristics of the paper surface and type itself and even humidity. There is no simple depth sensor that would work.
The best you can do is to measure the distance from the top of the stack to the sensor, but the precision of the sensors is going to likely be way too high for accurate measurements of individual sheet counts.
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There is a way to measure the thickness of something by going around it, though.
Put a flat plate behind the object. Have your sensor holding completely still, and measure the distance to the plate. Then, place the object in, without moving either the sensor or the plate. Finally, subtract the distance to the object from the distance to the plate, and you get the object's thickness.
Nice approach!
That still requires a sensor with extremely high precision, if you want an accurate count to the level of an individual sheet (~0.1 mm). Depending on the situation, you might consider using a load cell with HX711 amplifier to weigh the stack. A sheet of paper has a weight around 4 - 5 g.
Very interesting the HX711 module!
You could try using attenuation through the paper. It does not have to be IR, it could be visible light.
Try an experiment; with your eyes look at source of light, put one piece of paper up in front of it - the light is dimmer. Repeat for two pieces, dimmer still. Keep going until you cannot perceive any change (I guess maybe 5 sheets).
If that is within your acceptable range of sheets, then you have a fundamental solution. You will need a light source, such as an LED and a photodetector, such as a photodiode with transconductance amplifier or light to frequency, I think Texas Instrument do one TSL230/35/45. I’ll leave you to research that.
Actually that's the idea behind my first approach, just the difference is that I don't want the light to be visible (so IR) but considering the limitations that garydyr mentioned...
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This will measure distances in the range 0.5 to 5 cm.
Sharp makes other models with other ranges. Perhaps one of them will be suitable for your (unspecified) range.
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