Infrared Emitter Detector Amplified Signal Circuit($50 robot)

[mobz]

If someone could tell me

1) why we need to amplify the output of the detector circuit?
2)Why do we give the phototransistor Voltage?(Vcc)

3)how do i modulate the the signal to avoid interference from ambient light?


Any input will be highly appreciated..

[frank26080115]

amplification is not really needed

also, to avoid the problem of ambient light, what i do is take a first reading, use a mosfet to turn on the emitter, take 2nd reading, turn off emitter, then compare the two readings for percentage difference