I'm using phototransistors to sense low speed data (about 7 bits a second). With one phototransistor and a 300K resistor, I found my sweet spot and can transmit correct data with lazer.
I find if the resistor value is too high, I won't be able to sense data, and if the value is too low, then the sensitivity is too restrictive.
The phototransistor I use is wired in a common-emitter fashion (with collector to +5V through 300K resistor). The model I'm using is PT334-6c. I'm not entirely sure on the value of the capacitance in that model but I know one exists somewhere since the manual indicates the rise and fall time is 15uS if the resistor is 1K.
For the remainder of my question, let's give this capacitance a value of X.
Now if I connected two phototransistors in parallel to each other (collector to collector and emitter to emitter) and have one resistor as the load, will the capacitance value be 2 times X and will I have to make the resistor half the value?
And what about if of those two phototransistors, one is completely covered so no light enters it, and the other one has the valid lazer pulses going to it? would the capacitance still be 2 times X? or just X because only one phototransistor is active?
How would the number of phototransistors that detect the pulses out of the total number of phototransistors in parallel affect the total capacitance of the phototransistor network?