Hi, i bought this photo transistor and connected it as showen in this schematic and it doesnt really work , i used an ultrabright led to shine light on a surface (black and white ) and measure the analog value , no voltage swings between white and black just few mV between both colors.
I tried 1k , 10k , 100k resistors and doesnt swing and 180K resistor it swings but with +- 2V between white and black ...
i dont know how to choose the value of this resistor ?
Its response peaks at infrared and is half the sensitivity with violet light at the other end of the visible spectrum. Red is at 80% to 90%.
It is sensitive to direct light. With reflected light it needs a very bright light, a very close and reflective surface and a very high value (1M?) for its collector resistor. An amolifier might be needed.
The datasheet says its collector current is from 0.7mA to 5.07mA when a very bright light shines on it.
You said the transistor did not have an output with a 10k or 100k collector resistor. It is 10 times more sensistive with a 1M collector resistor.
The 1M includes the load you have on it. What resistance is the load?
i connect it to an LM324 compartor to compare its output voltage to a reference (( used in line followe robot to detect the color ( white or green) ).
i will try with 1M and ultra brigh red led .
You also might try putting some bias on the transistor base to kind of get a little collector current flowing before you apply the light and see if that gives a better resuld.
Google has hundreds of links to line follower robot circuits like yours. They use a 10k collector resistor on the photo-transistor and have enough sensitivity.
Maybe yours doesn't work because something is connected wrong?
Check the LED current and the pins on the photo-transistor.
I notice that the datasheet for the Taiwan photo-transistor does not say how tight is its focus. Maybe it has a very narrow window to accept light.
Then its numbers will look like it is very sensitive when it is just focussed instead.