Eagle imposible routing

[guidoilieff]

Some fundamental concepts:
1. Placement is king. Placement of parts can make routing trivial or impossible.
2. Good placement relies on placing parts that are most heavily interconnected as near one another as possible. The idea of having connection "rubber band" connections was concocted to make people think that connections actually had pull on the parts they connected, so that the circuit would contract on the pull of the connections to the most closely connected placement, or very near it.
3. Minimum cut-set. IF you have a set of connections, as in IC1-pin2 to IC4-pin7; R3-pin1 to IC3-pin3 (and on for all of the hundreds of connections), a minimum cut-set of two means you only have to cut two connections to separate the circuit into two independent sections. A cut-set of three only needs three connections cut to separate it into distinct parts. Placement can be based on minimum cut-set, then increasing cut sets, to literally sort the interconnections out, for further rubber band placement.
4. Scorable nets. Auto routers sometimes use a polynomial to calculate the "goodness" of placement, then routing. Things like shortest total length of all traces combined, smallest PCB area, smallest number of layers, etc. go into this calculation. People found early on that you don't need to score all the nets to figure out a good layout. For instance, you can usually ignore ground, not because it doesn't matter, but because it has to go EVERYWHERE so it doesn't make a difference in the scoring. Similar for power, bias nets, etc. that go lots of places. You're looking at the differences in connections, not the sameness of connections.

But all this sophistication is to arrive at good placement. Placement is king.

I'm having a hard time with the concept of rubber band connections, I guess my english is not that good so point 2 and 3 are a little hard to imagine for me, im sorry.

[guidoilieff]

i always with basic from RG, or Jack AMZ? i forgot
start from left is input, and right is output
its easiest to draw. And Runoffgroove teach me the simple way

im lazy too etched, so perf its the fastest way
then, i jealous with perf wizard like Rick freqcental, Jon midwayfair and Russ Cozy, their layout is amazing
convert perf to pcb is easy

because the trouble in perf is mood to build, and hard to modify
move on to pcb, madbean have some good tutorial to make pcb. i follow

in the end, found unreal style like Jack Deville, look at his delay
or OCD-ish like bugg, how they can layout like that? amazing art

i must mention some 1590A builder, ex pickdropper, thomasha
their own layout is unreal too

the best lesson is from local store owner
want make your own layout?
imagine first, draw some variant, then decide what suit you
but please, no autorouter. Kill your creativity

thanks, I'll check em out!

[R.G.]

I'm having a hard time with the concept of rubber band connections, I guess my english is not that good so point 2 and 3 are a little hard to imagine for me, im sorry.

No  need to apologize. I strongly suspect that your English is better than my gasp of your native language. 

On item 2: imagine that every connection is a little rubber band that connects the pins that should be connected, according to the schematic. The rubber band is at zero tension when the two pins it connects are right next to each other. As you move the two parts that have the pins on them that the rubber band connects, the rubber band stretches, and tries to pull the two pins back together. The further apart the two parts get pulled, the longer the rubber band stretches, and the harder it tries to pull the pins together again. So for only one connection, the imaginary rubber band pulls the pins back together again if it can.

Now imagine that there are not just two pins connected together by one rubber band; imagine two ICs, each with several pins that ought to be connected to one another. And other pins on the two ICs connect to isolated resistors and caps. The little rubber bands will try to pull the two ICs together, there being several of them pulling on the two ICs, but each resistor or cap only gets one rubber band, so the ICs will tend to be pulled together in the middle, and the resistors and caps pulled closest to the pins they connect to.

The shortest total length of all the rubber bands is what would result, and that turns out to be good for running PCB traces instead of rubber bands. It also happens that the shortest total length of traces is easiest to route as well, and that's why the "rubber band" idea is good for layout, and why PCB routing programs show those "rubber band" connection lines.,

On Item 3, the idea of the minimum cut set is the opposite of the rubber bands idea. If you have several ICs with associated resistors and caps in a schematic, you find places where if you were cutting the connection "rubber bands", you would have to cut the fewest rubber bands. So if you had three ICs, and two of them were connected by 5 rubber bands, but the third one only connected to the other two by two rubber bands, you could separate the third IC by cutting only two "rubber bands". That tells you that the third IC is more loosely  connected to the two many-connections ICs, and can be placed further away on the PCB without messing up the traces to the other two ICs.,