Currently my school project group and I are working on a robot. We received a pnp optical sensor. We've been told that we have to use a 120Ohm resistor between the ground and the sensor output signal. Well, the robot worked and right now we are writing our report. In it, we have to specify why the resistor was needed. Unfortunately we have no idea and are having trouble finding it on the internet. Does anyone know why we need a resistor between the ground and the sensor output? Thanks in advance!