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Questions relating to designing PCBs
By mattmunee
#183848
I just finished my first PCB design. I basically just took the designs from a couple different boards and put them together on one board. It's designed to be like the Moteino with an accelerometer and LiPo charger on board. I'd appreciate any pointers on what I've done wrong! In some cases, I opted for long traces instead of added vias because I've heard that vias are not ideal, but I'd be interested to hear your comments. Thanks in advance for your time!
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By Ross Robotics
#183863
Schematic:
Pull up resistor on RESET is not connect to positive. Hold alt and drag it over to attach it to the net.
I would use 4.7K for the I2C pull-ups, but 10K should work fine.

Board:
Related to above: Need to run trace for reset..
The tiny lettering prolly won't be printed as it's too small for most houses.
No need to put values on board since they are mainly used on the schematic to generate a BOM.
Anything 90 degrees or below may cause acid traps. Traces should have 45 only. Also when a trace touches a pad should be at 90 deg. I usually have the traces come in on a corner of a square pad.

Still looking through it as the above is minor except for RESET.
By davep238
#183867
I agree with Codlink, though I think that 90 degree junctions are OK. However, I have concerns about your schematic. Parts should be on a 0.1" grid. It looks like most of your parts are on a 0.05" grid, but some of the parts aren't on that grid either. The reset resistor is an example of this. I am really puzzled about the voltage regulators. It looks like the output of IC1 (3.3v in, ??v out) is connected to the output of U2 (4.2v ?? out) which is a battery charger chip. This net is labeled "PWR". What should the voltage be at this point? And is this board supposed to be powered by the USB port or via the SPI port?
By mattmunee
#183869
codlink wrote:Schematic:
Pull up resistor on RESET is not connect to positive. Hold alt and drag it over to attach it to the net.
Well, crap. I should've seen that one. Thank you!
codlink wrote: The tiny lettering prolly won't be printed as it's too small for most houses.
So what's a rule of thumb for typical screen print letter sizes?
codlink wrote: I usually have the traces come in on a corner of a square pad.
What do you mean by this? Are you saying you come of the pad at an angle, instead of straight off the edge?

So are acid traps a problem for junctions only, or any turn on a trace? Also, do this usually come up during the manufacture of the PCB or during assembly?

Also, any guidance on standard trace widths?

Thanks, codlink!
Last edited by mattmunee on Wed Aug 05, 2015 5:24 pm, edited 1 time in total.
By mattmunee
#183870
davep238 wrote:Parts should be on a 0.1" grid. It looks like most of your parts are on a 0.05" grid, but some of the parts aren't on that grid either.
Thanks for taking a look, davep. I guess I wasn't too concerned about having my parts or schematic aligned to a grid, so long as they passed the DRC. Is that a requirement by some fab houses? I assumed it was critical to maintain a minimum trace/part/pad separation, but I didn't think that keeping a grid would be that important.
davep238 wrote:I am really puzzled about the voltage regulators. It looks like the output of IC1 (3.3v in, ??v out) is connected to the output of U2 (4.2v ?? out) which is a battery charger chip. This net is labeled "PWR". What should the voltage be at this point? And is this board supposed to be powered by the USB port or via the SPI port?
Well, crap, it looks like my regulator is backwards. The PWR net should be the input of the regulator, which is also connected to a battery, which is also connected to the output of the battery charger. The board should be powered by battery or USB, not SPI.

Here are the boards that I cobbled together for this design:
https://github.com/LowPowerLab/Moteino/tree/master/R4
https://www.sparkfun.com/products/10217
https://www.sparkfun.com/products/12756
By mattmunee
#183884
mattylad wrote:What is SP1 for? as I see only 1 track on it.
It's my understanding that I can program the Arduino bootloader using SPI and another Arduino.
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By Ross Robotics
#183886
mattyland is talking about SP[one]. I think matt is just using it for power...
By davep238
#183888
davep238 wrote:Parts should be on a 0.1" grid. It looks like most of your parts are on a 0.05" grid, but some of the parts aren't on that grid either.
mattmunee wrote:Thanks for taking a look, davep. I guess I wasn't too concerned about having my parts or schematic aligned to a grid, so long as they passed the DRC. Is that a requirement by some fab houses? I assumed it was critical to maintain a minimum trace/part/pad separation, but I didn't think that keeping a grid would be that important.
The schematic is not used by fab houses, only the Gerber output files are. However, if parts aren't on a grid, sometimes they won't connect.
davep238 wrote:I am really puzzled about the voltage regulators. It looks like the output of IC1 (3.3v in, ??v out) is connected to the output of U2 (4.2v ?? out) which is a battery charger chip. This net is labeled "PWR". What should the voltage be at this point? And is this board supposed to be powered by the USB port or via the SPI port?
mattmunee wrote:Well, crap, it looks like my regulator is backwards. The PWR net should be the input of the regulator, which is also connected to a battery, which is also connected to the output of the battery charger. The board should be powered by battery or USB, not SPI.
According to the schematic, the VCC pin of the SPI connector is connected to 3.3v. This pin can not supply 3.3v if the board also supplies it. Also, be aware that inputs are shown on the left and outputs are shown on the right on schematics. The 3.3v output of the regulator should be shown on the right of the part (as it is currently shown). So don't just reverse the regulator when fixing the schematic. You may need to have a battery connected to the charger chip for the circuit to work. I don't think that the charger chip will supply much current without a battery. Talk to Sparkfun about their 10217 charger board to see what happens in that situation.
mattmunee wrote:Here are the boards that I cobbled together for this design:
https://github.com/LowPowerLab/Moteino/tree/master/R4
https://www.sparkfun.com/products/10217
https://www.sparkfun.com/products/12756
By mattmunee
#184019
All,
Thanks a lot for the previous notes. I've tried attached a redesign with a few changes.

1. I've tried to hold to a 45-degree trace angle as well as I can. On the fine pitch parts, that's not always possible.
2. I've added "load sharing" capability to the charger circuit. When the USB is attached, the battery is disconnected from the main circuit. (See http://blog.zakkemble.co.uk/a-lithium-b ... d-sharing/)
3. I've added a few more ground vias to help with noise.
4. I've changed all my text to a more readable size and vector font
5. I've double checked that all of the parts on the schematic are actually connected!!!

Questions: I get a few "solder mask" errors in Eagle. How would/should I correct these?

Any major red flags? I really appreciate everyone who takes the time to review my design! :clap:
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By Ross Robotics
#184021
You don't need Gerbers when dealing OSH Park and Eagle. Just upload the brd file.

There are 2 dimension errors concerning ink over lapping solder mask
The other dimension error is half the word "USB" is over lapping a solder pad.

When you run the DRC, double click on an error and it will take you to it.
By n1ist
#184038
You may want to also post pdf versions of the schematic and board here; not everyone is an Eagle person...
/mike
By mattmunee
#184046
I've attached PDFs, and also modified Eagle files, based on some suggestions I've received. One question I have in particular, is concerning the "Stop Mask" errors when I run the Sparkfun DRU (which I've included in the Eagle Files zip). Yes, I know that double-clicking will show me where the error is, but I don't understand how to interpret the error or fix it. They appear beside the Atmel chip, at a single resistor, and at a 2-pin header. Can anyone explain if/how I should fix these?
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