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Author Topic: Photometer  (Read 947 times)
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Vineyards
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« on: December 25, 2014, 12:29:55 00:29 »

Photometers are used for determining the concentration of a matter dissolved in water. They generally use an LED source emitting light mostly on a certain wavelength and an optical resistor as a sensor. The equipment measures the light passing through the sample and then a reagent is added which gives the solution a specific color.  The measurement is repeated and the two readings are correlated. Some devices may also use wavelength specific filters.

There are color measuring sensors on the market although I have never had a chance to study one. Has anyone had any experience with them. Do you think they are sensitive enough to say, to automatically detect specific colors, their illuminances and produce a reliable measurement? Each reagent produces a specific color and the color generally goes darker as the concentration increases. 
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CocaCola
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« Reply #1 on: December 25, 2014, 01:05:26 01:05 »

Depends on how accurate you need to be, in a controlled environment you can do wonders with a simple webcam...
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Vineyards
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« Reply #2 on: December 26, 2014, 02:49:54 14:49 »

What sort of an interface do they require? Could it be done with PIC?
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xeontory
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« Reply #3 on: December 27, 2014, 02:01:08 02:01 »

You shall not need any wavelength specific filters if you plan on using LEDs as the sensor instead of Light Dependent Resistors. An LED works as a very good sensor, close (slightly higher) to the specific wavelength that it emits. Generally, an yellow LED works as a Green Color Sensor, a blue LED works very good as an UV sensor. It output voltage can go as high as from several hundred milivolts to 1.5 Volts with bright exposer which you can even cascade to get enough voltage to sense directly with an ADC of an MCU. Resistive sensors are not all equal and needs a lot of calibration for each of them where as normal LEDs used as sensors show almost identical characteristics. As its output is analog you can amplify or digitize with required precision / sensitivity. They are cheap comparatively if you want to "study one".

Again, I agree with CocaCola, imaging with a camera will be the easier to implement, with better accuracy and precision for the determination of color shades if you have the option to use one. 
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Gallymimu
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« Reply #4 on: December 27, 2014, 06:00:57 06:00 »

I would do this with specific wavelength emission and then a generic silicon detector rather than trying to make the detector wavelength specific.

Real spectrometers use gratings / prisms and linear sensor arrays which are also pretty cheap.

I've done discrete spectrometry using LEDs and silicon detectors for identifying coatings on glass.
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