i would like to know why it is needed to put a 10k resistor in series with the phototransistor.
As far as i could find out a transistor is something like an amplifier which can open the circuit with a very small current from the basis to let more current flow through the transistor emitter. So a small current flow from the base can amplify the current which flows from the power supply through the emitter with a gain factor proportional to the base current.
So far so good i think… but why the 10k resistor?
Thanks in advance