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Is it possible to make work LDR as color sensor?

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ikelectro

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I want to make a color sensor using normal LDR. I'm barred to use ready made color sensor or module like. I have gone through some of the website regarding that. But as far as I able to search, can't find any information which will help me. So, I need your expertise in that subject, want some valuable information from you guys .
 
Google: LDR color sensor

Ken
 
So, you are saying that I have to put light and some color paper in front of the LDR to sense different color! Correct me if I'm wrong.
 
If you want to distinguish multiple colours you will need multiple LDRs with respective different colour filters; or you could present the different filters in turn to a single LDR. You could, for example, use 3 LDRs with 1 red, 1 green and 1 blue filter respectively.
 
Ikelectro, If you were closer to me I would give you light filters.
Can you get colored glass? Maybe from broken bottles.
People make pictures with small pieces of colored glass. (church windows) Here there are hobby stores with colored glass.
As Alec_t said; you need three filters. Red, Green and Blue glass will work "OK".
 
So, you are saying that I have to put light and some color paper in front of the LDR to sense different color! Correct me if I'm wrong.
The colors of "what" do you want to detect in this project?

Ken
 
Ikelectro, If you were closer to me I would give you light filters.
Can you get colored glass? Maybe from broken bottles.
People make pictures with small pieces of colored glass. (church windows) Here there are hobby stores with colored glass.
As Alec_t said; you need three filters. Red, Green and Blue glass will work "OK".

It's great to hear from you and feeling very sorry I'm not nearer to you.:( As far as my locality, probably it will tough to get color glass. But I can get these which called as cellophane paper.
Will they work? What do you think?
 
Hi,
primarily I want to stick on RGB.

I would say those cellophane papers will work OK.
Some members in the past have used the coloured wrappers from children's sweet's. [ boiled sweets, toffee etc]

Eric
 
Ldr's are a good choice, you might find different colours will give different outputs, so you'll have to callibrate the device, also ldr's might not be as quick at responding as photo trannys so give them enough time to respond, esp if your using a quick processor.
 
I recall a design appearing at Electronics Now or Radio Electronics. It worked differently: 5 (or it was 6?) LEDs of different color shining their light in turn and the LDR response measured for each one.

The profile (combination of all those readings) received a name which allowed to identify samples of the same (combination of) color.

Designed by two or three guys (IIRC) from an university in USA (or it was Canada?). Tried to contact them with no luck.

It used no micro.
 
Interesting approach, I wonder if it used a decade counter and some sample/hold circuits.
 
Interesting approach, I wonder if it used a decade counter and some sample/hold circuits.
I recall it being really simple. Since yesterday trying to retrieve more details from memory.

NF: nothing fancy & no filters. IIRC, of course.
 
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I recall a design appearing at Electronics Now or Radio Electronics. It worked differently: 5 (or it was 6?) LEDs of different color shining their light in turn and the LDR response measured for each one.

The profile (combination of all those readings) received a name which allowed to identify samples of the same (combination of) color.

Designed by two or three guys (IIRC) from an university in USA (or it was Canada?). Tried to contact them with no luck.

It used no micro.
Our Geology Department has several commercial ones like that.

Ken

Added: This is the unit: https://www.lpi.usra.edu/education/products/spectrometer/
On the bottom is a ring of 11 narrow band LEDs , with one wide band detector in the center. Calibrated against white paper.
 
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When I was a kid in elementary school (long, long ago) I did a science fair project I called SoC (Sound of Color). I used a simple LDR with a small incandescent flashlight bulb. The lamp was angled to shine light on a color and the LDR angled to measure the reflected light off the color. The LDR and Lamp were sort of like a letter V where the bottom of the V is the reflection point. The idea being a color like black absorbs more light than white which reflects more light. I used mat finish colored construction paper to demonstrate. The LDR was part of an audio oscillator circuit and the audio tone frequency changed based on the color. It was simple and crude but worked well.

Ron
 
Our Geology Department has several commercial ones like that.

Ken

Added: This is the unit: https://www.lpi.usra.edu/education/products/spectrometer/
On the bottom is a ring of 11 narrow band LEDs , with one wide band detector in the center. Calibrated against white paper.

Gracias Ken. Good reading.

Maybe I should read it twice again but it is not clear what part of the design ensures (some?) repeatability in the results. Or it is that I am asking for something they are not offering??

Could I asume that each LED in every ALTA is reliably emitting in the same wavelength? In other words, is any ALTA able to give the same results for the same sample? (Accepting that "same" involves a certain tolerance).
 
The ALTA is not a high end spectrum analyzer. The calibration is to check each channel against a piece white paper to get raw numbers for that unit. As you probably know, there is white and WHITE and WhItE . ;)

Ken
 
Hi everyone,
As it seems to me that I have to fixed the light source,LDR and color object at fixed location. Because I'm observing that distance from LDR to object hugely affected the reading value.
 
The absolute value of the LDR signal will obviously vary with distance, but I would expect the ratio of measured values when using respective filters or LED colours to be more or less insensitive to small distance variations.
 
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