R? is selected to give about 1v5 across the red LED (probably in the region of 330R) this only necessary because the 1v5 scales have the cell +ve connected to the metal body, so to avoid grounding problems I've shifted the PICs Vss supply (and the scales own Vss) 1v5 below the system (PC and Machine) ground.

If your scale has a 3v lithium cell you may have to rethink the power supply, because I'm not sure if the 3v scales have their metal body connected to the +ve end of the cell or not (none of mine are 3v) .

The other LEDs in the outputs are just to limit the voltage to the scale when the PIC output commands.