hello everyone,
i hope you having a good weekend start
i've been learning eagle the last 4 days, i started on Tuesday got the basic, Wednesday i learned how to make a custom library (packages, symbol and whole device) yesterday made my schematic and today i am making the PCB and routing. Happily everything went well and i feel i need to learn more about Eagle, the last time i tried to learn it i didn't like it much so i did not start, but this time it was a must and i liked the way it works with scripts and others.
I would like please your opinion about my PCB (attachment file for its picture and schematic) and if there is anything to make better, and i would like to know if the 0.006 inch would be good for the Traces in this case ? and how to know the width in general ?
I usually default 0.016" for traces - unless you need to make it thinner for some reason, which I don't think you do in that case? 0.006 is pushing what some of the cheap fab houses can do.
I go thinner if I need to in order to make the routing work while passing the DRC check.
I make power traces, or traces otherwise expected to carry a heavy load, wider (0.024, 0.032, or even more if particularly high current is involved).
I don't see any decoupling caps on the three left hand shift registers.
You have the cathodes of your LEDs connected to Vcc - how do you plan to turn them on?
Edit: Net classes, set the default widths there.
6 mil is kind of thin, I plan for 10 or 12 mil wide, 10 mil clearance, 12 mil vias.
Wider on power traces, like 20 or 24, with 24 mil vias.
Draw a polygon around the whole board, on both layers, and name them Gnd.
If you select Autoroute, go to View:Grid and select mil for units.
Then when autoroute opens, select 5 or 2 for grid size to use. Otherwise I think it opens at 50 and a lot won't get routed for you.
about 0.006 inch, it was written in SparkFun tutorial which i used but it's good that i asked this question because i didn't know it was on the edge and need heavy manufacturer
@CrossRoads oops i didn't notice i flipped the signals, lol i corrected it now thanks for noticing
about the polygone you mean to make all the boards GND and the traces in between ?
in sparkfun tutorial they talk about that, i will see if it's what you mean but can you please explain to me why is that done for GND ? why all this big surface ?
Edit Correction:
sorry guys my memory failed me this time, sparkfun suggested as default size 0.02" but no less than 0.007" and for Clearance they suggested 0.006 no less
DrAzzy:
I usually default 0.016" for traces - unless you need to make it thinner for some reason, which I don't think you do in that case? 0.006 is pushing what some of the cheap fab houses can do.
I go thinner if I need to in order to make the routing work while passing the DRC check.
I make power traces, or traces otherwise expected to carry a heavy load, wider (0.024, 0.032, or even more if particularly high current is involved).
my reason to go thin is the place i have as you can see it's very tight so i must save space but the dimensions you suggest with CrossRoads are totally fine in term of space
You could also ditch the 3 shift registers and have the MAX7219 that is driving 1 display drive the 24 LEDs as if they were just 3 more displays. Wire them in groups of 8 with a common anode per group, and connect the A segments together, the Bs together, etc, with the ABC from the lone display.
You have plenty of space for routing, that is not a dense board.
Ground plane helps with routing Gnd signals, helps with power supply capacitance, helps reduce EMI emissions, etc.
CrossRoads:
You could also ditch the 3 shift registers and have the MAX7219 that is driving 1 display drive the 24 LEDs as if they were just 3 more displays. Wire them in groups of 8 with a common anode per group, and connect the A segments together, the Bs together, etc, with the ABC from the lone display.
You have plenty of space for routing, that is not a dense board.
Ground plane helps with routing Gnd signals, helps with power supply capacitance, helps reduce EMI emissions, etc.
ok great about the space i am glade you make it clear for me because i thought for a moment i had a dense board hehe
about the max7219 no it would be very hard job and it's a CA single digit so the max is configured to work for CA that's why it's not going to work for the LEDs, the third shift register is to driver the A B C of the 4051 analog multiplexer and that's how i would save pins from arduino
Power and ground traces are wider so to have less inductance, not to carry more current (unless its
significant current levels of course). Try to have 32 or 40 mil minimum for power and ground. 10 mil
or less is generally adequate for signals. Check with your PCB fab house about design rules.
With only two layers its tricky to get good ground plane coverage of a dense board, you generally
do polygons both sides and link them with explicitly placed vias (named GND) until all the ground
pins of the components link up.
Surface mount is much easier to route, since most signals are top side and you can hop them to
the underside as necessary without breaking up the ground plane there much. Using solder paste
and toaster oven with a laser-cut stencil is my preferred approach and the results are professional
looking. Surface mount parts in SOIC packages aren't too difficult to hand solder if that's all you
have available. Practice on scrap boards first!
MarkT:
Power and ground traces are wider so to have less inductance, not to carry more current (unless its
significant current levels of course). Try to have 32 or 40 mil minimum for power and ground. 10 mil
or less is generally adequate for signals. Check with your PCB fab house about design rules.
With only two layers its tricky to get good ground plane coverage of a dense board, you generally
do polygons both sides and link them with explicitly placed vias (named GND) until all the ground
pins of the components link up.
Surface mount is much easier to route, since most signals are top side and you can hop them to
the underside as necessary without breaking up the ground plane there much. Using solder paste
and toaster oven with a laser-cut stencil is my preferred approach and the results are professional
looking. Surface mount parts in SOIC packages aren't too difficult to hand solder if that's all you
have available. Practice on scrap boards first!
but isn't 32 very wide ? i am using 20 like CrossRoads adviced
i reached this point that you can see in the attachment file, at this point i clicked autorouter but it failed to finish all the connections so i tried to do it my self and got stuck
any idea what can i do ? i am using the 20mil for GND and Vcc and 10 for the signals
about the max7219 no it would be very hard job and it's a CA single digit so the max is configured to work for CA
Incorrect, max7219 is designed with common cathode in mind.
The MAX7219/MAX7221 are compact, serial input/output
common-cathode display drivers that interface
microprocessors (μPs) to 7-segment numeric LED displays
of up to 8 digits, bar-graph displays, or 64 individual
LEDs.
Wiring the LEDs as if they were digits is very easy to do as well. Save the space of 3 shift registers and all the resistors.
When you click the autorouter, did you first select View:Grid and change it to "mil", and then select 1 mil for the autorouter grid?
You will find initial designs to be difficult until you start learning about such things.
And placement is very important to getting a board that can be routed, either auto or by hand.
If the autorouter is struggling, then parts placement is usually not good. Move around what you can, and look into simplifying the design, making better use of the hardware you have.
I never autoroute with Eagle, because it cannot handle a tight layout. If you have lots of spare
board area it will complete, but its rather a dogs breakfast in my experience.
I autoroute as a first step always, gives me good feedback on whether the placement is good, if parts need to be flipped 180, etc.
With good placement, routing can often complete with just GND connections needing some work, and maybe power if the trace selected is wider than the SMD pads used.
Often times a trace route can be adjusted to make room for ground fill or to let fill areas connect, or adding GND vias will let things connect by connecting top & bottom layers.
If you have a specific path that you want a bunch of parallel runs to make, then adding those by hand are needed, can do that and then let the autorouter fill the rest.
Sometimes a trace will be all over the board, ripping it up and running by hand will be needed to fix that.
In the end, it's just a tool, with different ways of using it working well for different people. I usually go thru after autorouting and get rid of right angle turns, adjust things like zig zags where changed layers but didn't need and eliminate vias, eliminate layer changes leading to a thru hole part and getting rid of vias.
I don't know if Eagle can autoroute on one layer only with jumpers (also without jumpers), but the defunct WinQcad allows this.
Sometimes it does a great job. Next you do GND pours on the other side.
