Digital "mirror"

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Peter_24

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What effect is required?

There is a group of three LEDs: red, blue and green.
When we shine red light on this group, the red LED turns on.
If we shine blue light on this group, the blue LED turns on and so on.
Moreover, the brightness of the LED is proportional to its illumination.

Approximate implementation:

When the LED is illuminated with light of the appropriate wavelength, a voltage proportional to the illumination appears at the LED output. In addition, the electrical resistance of the LED changes.

And this can be used to supply proportional voltage to the same LED.
At some points in time, we measure the voltage at the LED output or its electrical resistance, and at other points we supply voltage to it.
That is, the LEDs should work as a kind of mirror, reflecting external lighting.

Questions:

How can this be implemented in hardware? Is it possible to use microprocessors like Arduino for this? Can such processors perceive analog voltage and produce the corresponding output voltage? Where can I read about this?
 

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1st you need optical colour filters or a tricolour sensor. This is an analog current mirror problem as voltages are non-linear from impedance.

2nd you must define how far from tru colour mirroring you can tolerate or prefer in terms of bias to the strongest colour if you want more vivid colours.

3rd define your RGB LED with a datasheet and power supply you would like to use. Mirroring can also be converted to PWM for better efficiency and smaller heat sinks.

Doing everything digital is possible but depends upon your budget for time and materials to do the work.
 
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There's a paper "Photo-reception properties of common LEDs" indicating that emission and reception wavelength of common LEDS don't generally match, in some cases not even overlap. In so far the design idea isn't expected to work.


In any case, you cant send and receive simultaneously, time multiplex would be required.
 
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It's weird from a school physics point of view, but OK, thanks.
 

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Hi,

.. and - even if you build a huge array - it can´t work as a mirror to reflect an image.
Because mirrors reflect according angles. It is working directional according input_angle = output_angle.
So theoretically every very tiny mirror can reflect a whole image.

LEDs don´t work directional. It can generate only one color in time and this color is spread out over a wide range of angle.

In other words: If you use a huge array of your LED_mirrors ... you won´t recognize any image in that. All LEDs will produce about the same color and brightness.
Each "pixel LED" reproduces the average of all infalling colors from all angles.

Theoretically you could improve the mirror effect by using huge optics and dark housing.

Klaus
 
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Right now I'm remembering what cameras do. The old-fashioned type have a lens which focusses incoming light and forms an image internally. One popular model let you snap a picture, then remove the film and wait a few seconds to reveal a full-color photograph. Incoming light beams turned into film 'pixels' whose color matched each light beam.

I believe a similar lens is in my digital camera, and perhaps in my iPhone and my webcam. Electronically these pick up light beams and send data to a screen. This could be fashioned to resemble a mirror.

To do what you want I can't be sure if an image has to go through a lens and focus on a CCD. Perhaps a beam-splitter contrivance can make it possible.
 

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