ITEM NAME:DIY Smart Robot Car Electronic Assembly Kit With Reduction Motor K D3O5 Description&Preview.Step 1: Welding circuit. Step 3: The installation of a photoelectric circuit. Photosensitive resistance and light-emitting diodes (note polarity) is reverse-mounted on the PCB, and the ground distance is about 5 mm, both photosensitive resistance and light-emitting diodes are 5 mm distance.