Takes an input signal and fills those items on two belts. When the signal changes, the belts empty themselves and stop automatically when old items are gone.
The input signal must be a binary encoded signal and places the item at bits 2, 4, 8 and 16 onto their own lane on the 2 belts. If you wanted the left belt to be full of copper playes, send a signal of 6 (2 + 4).
At the very bottom, a final conveyor belt segment is wired up so it will 'exhaust' (turn on) so all items loop back into main warehouse. It does this automatically if there are any contaminant items on the belt. See the video below!
Video with 4 levels of Science Packs
https://imgur.com/a/gnQ2Z
The above link is an example with me configuring it with 4 levels of science production (bobs mods), and using Crafting Combinator to set the recipe of anything > 32 (beyond the binary encoded values used for belts)
Belt contents being replaced: