OK, let's be clear here.
Wherever you found that picture on the Internet, it is total nonsense!
You do not wire simple sensors to the Tx and Rx pins on an Arduino.
The sensor output - we have yet to determine in the current to-and-fro conclusively whether it is one or two "phases" but as Paul_KD7HB points out, the printer itself has determined the direction, so there is actually no need for a second channel to determine that.
You will then have one output to connect to an I/O pin - not Tx or Rx on the Arduino. Even on a Leonardo where Tx and Rx are not connected to the USB interface and are actually available for other serial communications.