I am trying to build an IR sensor module for line following robots, and I used QTRX-MD-06A module as my reference. The principle and PCB photos are attached here.
However, the component with a circle mark that is beside 47K resistor on the PCB is something I never saw before. I don't think it is a zero ohm resistor, because if it is, it means the light emitting diode will be directly connected to +5V and GND without any current limiting resistor. It would burn the diode, wouldn't it?
Would anyone please let me know what it is? How does it relate to the current source symbol in the principle photo? Thanks in advance!
It turns out, there is a dedicated LED driver IC connected to the cathode of the light emitting LED. I guess this IC controls the LED current, and thus there is no need to use a current limiting resistor. So that component is indeed a zero ohm resistor.