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LDR Grid + Smartphone = ? Answered

Hi,

I've got an idea but I don't know what it can be used for, yet. Maybe you'll have some ideas for useful applications based on this concept.

The idea is to make a grid of LDRs which fits the size of a smartphone/tablet screen, write some code which draws a similar grid on the screen (or just switch images of that grid) so that each LDR will be affected by the light (and color) provided by each cell from the screen.

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Jonathanrjpereira

3 years ago

You could use it as a Physical Colour Passcode. Lets say your working on a project like a Smart Door Lock & the password is the arrangement of the colored blocks on your smartphone screen. Inorder to unlock the door you have to place the correct arrangement of colored blocks on the LDR array scanner.

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niviniJonathanrjpereira

Reply 3 years ago

The question is what the advantage of it over camera (QR code)?

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verence

3 years ago

First, LDRs can't distinguish colour, just luminosity. Second, LDRs als slow. If you really want to something like that, switch to photodiodes / -transistors, they can do kHz. Third, while there are some valid fields of use for such a contraption (e.g. my bank uses a flickering 5 bit code on the screen scanned by the TAN generator) think about other, more modern options like WLAN, Bluetooth, NFC ...

What is the real problem you want to solve?

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niviniverence

Reply 3 years ago

For some reasons I thought that there is a correlation between color and luminosity. I guess, LDR is not the proper device.

I've got a single TSL230R chip and gonna try that today.

Actually, I don't have a certain problem to solve, just wonder if such a thing can work.

Thanks

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verencenivini

Reply 3 years ago

> For some reasons I thought that there is a correlation between color and luminosity. I guess,

Well, there is some correlation between colour and brightness, as yellow is more bright than blue, but that depends on the spectral sensibility of the sensor. If the sensor is more sensitive for longer wave lengths, a red may be 'brighter' for the sensor that a blue that is 'brighter' for humans.

> LDR is not the proper device.

LDRs are okay for things like ambient light detection, simple light/dark decisions etc. The need some time to react to changes so are not good for data transfer.

> I've got a single TSL230R chip and gonna try that today.

Now, that's a different league. :-) Of course with this device you have to solve the problem of frequency measurement (i.e. using timers) instead of voltage measurement (ADCs). Do not use it for commercial developments as it seems to be discontinued, though.

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niviniverence

Reply 3 years ago

There's the TSL235R which would be perfect for that and got only 3 legs, Vcc, GND and output. Frequency measurement, it's easy with Arduino. I've done that with the TSL230R.

Anyway, I can't find a real advantage for that over WIFI, BT etc.

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verencenivini

Reply 3 years ago

The 235R looks much like the 230R in a different package minus some 'programming' pins.

Advantages may be that you don't have to fight with LAN / BT protocol stacks and APIs. You can define your own protocol. And light is easier to block than radio waves, so eavesdropping (man-in-the-middle attack, spoofing, ...) is more difficult. Of course, even with a (or some) phototransistor(s) bit rate is poor compared to LAN / BT.

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niviniverence

Reply 3 years ago

Actually, I think that an array of photoresistors gives us a digital camera.

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caitlinsdad

3 years ago

Look into color QR code readers. You have to think about the limits of the resolution of the device and how dense you want to pack the pixels and what that means for the data you are trying to read.

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nivinicaitlinsdad

Reply 3 years ago

Some kind of a QR code reader is a nice idea. Thanks.