I need to measure the red or green or blue component of a light source. Are there any resistor or diode with this specific capability? I found some diode with rgb filter, but i'd want to know if there are something more specific.
thanks
Photodiode, ldr and light source
ldrlight-sensorphotodiode
Related Solutions
Important notice This is an IR diode: Daylight blocking filter matched with 870 nm to
950 nm emitters. IR photodiodes usually have an opaque black package, while visible light photodiodes are in clear packages. You could look for a photodiode (a phototransistor is even more sensitive) with an eye sensitivity curve. I remember having used the SFH3410 from Osram here.
Then the good news: a photodiode or phototransistor acts as a current source, so a series resistor is sufficient to convert the current to a voltage. In your datasheet the graph of figure 3 is the one you need. The reverse current varies between 1uA and 100\$\mu\$A. A series resistor of 10k converts this to 10mV - 1V. You could increase this to get a higher voltage, you'll have to experiment with light levels and resistor value to achieve a full range of 5V. Also keep in mind that the input impedance of the ADC is parallel to the measurement resistor, reducing sensitivity.
The graphs below are from the SFH3410's datasheet. If you keep in mind that you need a \$V_{CE}\$ of at least 0.5V (right graph), you'll be limited to 4.5V output from a 5V power supply.
Further reading:
SFH3410 application note
Digikey still advertises LDRs here.
A phototransistor would probably do a good job in your application. Diode with gain effectively.
Digikey cheapest - 14c each in 100's - pricing here
Datasheet
Many more types available.
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Best Answer
There are chips that already do what you want. There is really no need to build your own thing out of color filters and diodes.
Take a look at the TCS3103 or TCS3104 from AMS for example. They output three voltages which are proportional to the incoming red, green and blue light components.