Note: a photodiode is an expressly measured diode that does this job.
An LED is still a photodiode, as this blogpost noted. But you'll get more consistent results with a real photodiode (or phototransistor, if you want a bit of amplification added in)
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Obviously the diode works here and for this project. But given higher levels of sophisticated photosiodes (but still a similar circuit), you can choose photosiodes that detect infrared light
We humans light up like a light bulb in the infrared spectrum. So two IR Photodiodes is all you need for a human motion sensor.
A motion sensor detects motion by looking at two pixels of IR light. Motion is 'defined' as one pixel lighting up.... Followed by the second pixel lighting up. If only one pixel lights up, then no motion (it's just a glitch). Real motion should show up across both pixels in a slight time delay fashion.
IR Photodiodes (or phototransistors) are used because it's the spectrum of light humans shine the most brightly in, despite being invisible to us humans it's the best sensor at the electronics level for these purposes.
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There really isn't much electrical complexity to the motion sensor that this blogpost was trying to debug.
I would suggest building your own motion sensor as the next step in your EE journey.
No. Even if each LED was a good light sensor (it's not good) the control circuitry is output-only. And you need a lens, or else every pixel receives the light from all around it, and reads just the average brightness of the room.
The "D" in LED is "Diode", commonly referring to the "P-N Junction" and its capabilities.
A CMOS sensor is an array of thousands of photodiodes. So erm... diodes are _already_ used as the basis of modern digital cameras.
I guess building one out of LEDs (diodes designed to emit light, rather than receive it) is feasible but I can't imagine it'd work very well. If you build a big enough camera and calculate the right lenses, it probably would work. But it wouldn't surprise me if the proper size of such a camera was on the order of a 20-feet by 30-foot room (with a "camera sensor" the size of maybe 5-feet by 5-feet, composed of thousands of LEDs acting as terrible photodiodes).
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A proper CMOS sensor miniturizes all of that to happen on a micrometer scale, so you can shrink modern cameras down to... well... the size of our phones.
But the principles of light, sensors, and cameras in general work even with larger / inefficient objects. You just got to build a "large enough" camera to compensate for all the problems.
EDIT: And also what the other poster pointed out about the control circuitry. The circuits in a typical LED Screen are all "output only". There's no way for the information to come back / reverse the LED Screen because the circuits are already set. I'm assuming you're somehow building those circuits and have embedded them into the LEDs somehow.
An LED is still a photodiode, as this blogpost noted. But you'll get more consistent results with a real photodiode (or phototransistor, if you want a bit of amplification added in)
----------
Obviously the diode works here and for this project. But given higher levels of sophisticated photosiodes (but still a similar circuit), you can choose photosiodes that detect infrared light
We humans light up like a light bulb in the infrared spectrum. So two IR Photodiodes is all you need for a human motion sensor.
A motion sensor detects motion by looking at two pixels of IR light. Motion is 'defined' as one pixel lighting up.... Followed by the second pixel lighting up. If only one pixel lights up, then no motion (it's just a glitch). Real motion should show up across both pixels in a slight time delay fashion.
IR Photodiodes (or phototransistors) are used because it's the spectrum of light humans shine the most brightly in, despite being invisible to us humans it's the best sensor at the electronics level for these purposes.
---------
There really isn't much electrical complexity to the motion sensor that this blogpost was trying to debug.
I would suggest building your own motion sensor as the next step in your EE journey.