I have been working on a logic driven, single belt production line that is relatively easy to set up and can be extended without many problems.
All of it still uses 0.12 level tech.
Overview
The whole system consisty of three parts. A storage area for the finished products, a input area for externally produced materials (iron plates, circuits, ect..) and a production area with the assembly machines. The production process uses the logic circuit signals for the products.
If a storage chest contains less then the specified number of items (e.g. just 100 out of 150 fast inserters), a signal for that item would be send out to the network (decider sends out fast inserter as 1).
On the production side the assembly complex for the fast inserter reacts to this signal by activating the inserters for the assembly machine and the logic will also send signals for ever component needed by the factory to the network. These signals will activate their assembly machines and they will send out their needed materials so that the network always contains signals for every material/product that is currently needed/produced.
The production line is set up in a way to make extension easy. After the initial setup the sub areas can be chained together to extend the setup.
Demo Setup
Logic Wiring
External Item Input
Lets go over the different areas:
1) The storage area
The storage area consist of a smart inserter, two decider combiners, a provider chest and an optional lamp for each product that is stored.
The first decider checks if the chest contains enough items. If not it sends out the signal (0) to the inserter and the second decider (and the optional lamp). The second decider sends out the signal for the product if signal (0) is 1 and the inserter is only active while the chest doesnt contain enough items. This allows other assembly line to ask for a product without it being picked up when it passes the storage area.
2) External input area.
The external input accepts raw materials and products from other parts of the factory. Anything that is usually mass produced can be inserted into the system at this point.
The setup here consists of two smart inserters and a requester chest (a belt delivery system is possible but requires more space). One inserter picks up the parts that pass it and the next puts the items onto the belt if they are requested. This way the belt is kept clean of items that are not needed for the current production requests.
For some high demand items like iron plates, I put in multiple chests. These output of the additional chests is tied to the demand (if 5 assembly machines need iron plates the signal for iron plates will have a value of 5). So one output will always be active, the others only if the demand is greater then 2 or 5.
3) The production area.
The production area consists of two independant assembly machines with their logic. One product is produced by one assembly machine, one constant combinator, three decider combinators, an arithmatic combinator, four smart inserters a provider (or smart) chest and an optional lamp.
The first decider will check if the signal for the itemtype is on the network and put out the signal (0) as 1 if it is. The arithmatic combinator will multiply the signal (0) with the signal from the constant combinator (which sends out signals for all the items needed by the assembly process) and send the result to the network. This way the needed materials are requested.
The products from the assembly machine will be put into the chest (while signal (0) is 1) and from there out to the belt (also signal (0) has to be 1). Passing products will also be put into the chest at any time. This will clean up the belt once the product is not needed anymore.
The additional two deciders check the itemcount in the chest and turn of the input to the assembly machine once it passes the threshold (100 in this case).
This will prevent the chest filling up and the belt being filled up by the product if the rest of the line is too slow to use it up.
The production setup can be put in a blueprint once the wires are connected and then copied as many times as you want. For each production setup you only have to set the items marked in red after it is build. The green values can be adjusted, but this is optional. Also the powerstation has to be connected to the rest of the network.
The order in which the items are produced is not overly important, though from what I experienced during my tests putting sub-products like gears or copper wire in the front should reduce startup times for the production.
I had a lot of fun playing around with this and once 0.13 is out (stable) I might improve it further. But this setup is currently producing everything I dont need in mass quantities and it does a decent job.