Circuit network for science packs

[PetrGasparik]

Hi, I am trying to make independend one-belt system making red and green science pack.
For educational purposes,
- I want to make them packs only when there is a demand (there is less than X packs in a chest)
- the same with prerequisites like gears and belts (so I don't want to have a belt full of belts and gears and copper wires)
- and I want to use circuit network (green/red wires)

I tried to make it for several hours, but I failed. Mainly, I don't know how to request prerequisites.
I tried to make buffer chest with triggered input and output back on that one belt system.

Did you try that? Have you succeeded?

Thank you, Pegas

[British_Petroleum]

I'm not sure if I understand what you want to do... but you can setup the entire chain without any belts or chests, just with inserters between assembly machines and labs. This way you never produce any science packs or any of the intermediate items unless the lab demands them

[Lupoviridae]

The key is to use the pulse signal function of inserters when they are connected to a circuit network.

If you take an arithmetic combinator set to [Everything * 1 | Output Everything], then connect the input to the output you create a pulse counter that can keep a record of every item currently on a belt. Inserters placing items on the belt will pulse a signal of 1 and add to the count. Inserters taking off the belt can be attached to an arithmetic combinator set to multiply signals by -1, and will subtract from the count. The output of this counter can be added together to the count of items in your destination chests so that only the requested number of items are placed on the belt.

Note that you will also need to either delay the -1 signal or add an "overflow" inserter, or the -1 signal will reach the counter before the item is added to the chest, causing an additional item to go on the belt.