as 0.12 is making combinators available for use i thought what use they might have.
When I started the game long ago I envisioned my factory as something where the "raw" items are coming in on one belt and the "final" item is coming out. In between I envisioned one assembly line with one belt where the needed items are drawn from and the intermediate products are put on. At the end, only the final item would be left on the belt. Before 0.12 this kind of behavior wasn't possible and the two most common factory setups currently are the "main bus layout" and the "huge number of bots doing everything" layout.
To put my vision of a factory into action a controlled (=timed) flow of the items on the main belt is needed. Thus you have to control your input to the belt. One way to do this is by counting the items you put on it.
The basic setup is shown below: The smart inserter is putting a defined number of items (D) on the belt. For demonstrating purposes these items are then added back to the chest. As the inserter itself isn't acting as a sensor (what a shame), you have to count the number of items you take out of the chest. Thus a variable signal 0 (s0) (combinator 1) is created which is holding the current amount or items in the chest (circuits in this case). Combinator 2 than subtracts the current amount from the amount of the old timestep (s0). If the difference (combinator 2) is greater than 0 (so a item was took out and not in; if you change it to smaller than you would count the items put into the chest) the signal is put through.
Combinator 4 and 5 are a simple time generator counting up from 0 to E (400). Combinator 6 it generating a reset signal based on the time input. So every time the cycle is reset the amount of items you want to put on a the belt (D) is incremented by one and thus resetting your item counter.
Combinator 7 is where the magic happens: If the number of items drawn from the chest (s0) is smaller than the amount of wanted items (D) the signal is put through. As we will see soon, the inserter will stop working when this condition isn't true anymore. Therefore the manual incrementation of D by one through the timer is needed.
Combinator 8 and 9 are then generating the signal for the inserter which is working if D = 1.
As you can see at the bottom of the picture you can put it all into a neat 4 times 6 square so it doesn't need to much space. Also you can see a small addition to the systems which is checking if there are enough items in the box for the cycle. If this condition is true F (time step of the timer) is set es 1 (you have to change F in the first constant combinator to 0).
With this very basic control method it should be possible to build a factory where nearly everything can be build on one single belt and no items are "wasted" in big belt buffers. Also you save a lot of spaghetti belts

Now I would like to hear your thoughts on my vision and my try on finding a design solution for it!