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121  Using Arduino / General Electronics / Re: What is "ground shift problems"? on: January 07, 2013, 06:57:46 pm
Awesome!  Thanks again everyone!
122  Using Arduino / General Electronics / Re: What is "ground shift problems"? on: January 07, 2013, 06:52:48 pm
Thanks for all of the great replies everyone and I think I understand now.  So I mostly want to avoid a situation where the GND and PGND are sharing a single trace before they reach a ground plane?
123  Using Arduino / General Electronics / What is "ground shift problems"? on: January 07, 2013, 04:40:11 pm
On page 13 of the attached link, under the heading "Synchronous Operation", paragraph two is the sentence "Both grounds must be connected on the PCB at only one point, ideally close to the GND pin."  What does this mean in terms of board layout?  On page 17 is a picture of a recommended board layout which appears to show both GND and PGND connected to the same ground pad that the part's exposed thermal pad is soldered too.  What am I supposed to be avoiding here in terms of PCB layout?

http://www.ti.com/lit/ds/symlink/tps61201.pdf
124  Using Arduino / General Electronics / Re: Understanding a land pattern on: January 06, 2013, 06:20:41 pm
Thanks everyone!  Sometimes I get my perspectives mixed up smiley-confuse
125  Using Arduino / General Electronics / Re: Understanding a land pattern on: January 06, 2013, 12:02:52 pm
At the Top of Page 4 a label  titled "Pin Assignments"...
Quote
DSC and DRC PACKAGE
(TOP VIEW)
and the pins numbered from the left side down in a CCW directiion.

Bob

Ah......that makes sense.  Thanks!
126  Using Arduino / General Electronics / Understanding a land pattern on: January 06, 2013, 09:45:45 am
I am thinking of using the TPS61201 to supply 3.3V to my arduino project and it comes in a SON-10 package.  I am having trouble understanding the land pattern and the pad numbering on the last few pages of this data sheet:

http://www.ti.com/lit/ds/slvs577c/slvs577c.pdf

When I am looking at the page titled "Thermal Pad Mechanical Data" it shows the pin numbering as well as a pin 1 indicator on the thermal pad.  I just can't tell how I am supposed to be looking at it.  Is the drawing from the vantage point of a part that has the pads down on the board and I am looking at it from above, through the part to the pads....or am I looking at it as if the part is flipped upside down on its back and I am looking at the pads from the bottom?  It will make a difference as to how I number the pads in my land pattern.  If it is from the top looking down through the part then pad 1 on my board will either be in the top right or bottom left and if I am looking at it as if it is flipped upside down on its back then pad 1 on my board will either be bottom left or top right.
127  Using Arduino / General Electronics / Re: PCB Routing Tips? on: December 29, 2012, 05:10:16 pm
What would we consider to be non-trivial current as it relates to a .008 wide trace?  You can assume I am using the standard board associated with this service:

http://imall.iteadstudio.com/open-pcb/pcb-prototyping/im120418001.html
128  Using Arduino / General Electronics / Re: PCB Routing Tips? on: December 29, 2012, 02:00:42 pm
At the top of the IC on the left side there's some really fine lines that look like nets that didn't get routed.  It's a good start though!

Ya there is a couple that didn't get routed that I will have to do by hand.  I'm just wondering if the liberal use of vias to make things happen is a bad sign regarding my component placement.
129  Using Arduino / General Electronics / Re: PCB Routing Tips? on: December 29, 2012, 01:59:34 pm
They always look ugly, with more than a couple of traces. However, you should look
at the top and bottom trace layers separately to get a better idea of how the layout
went. Also, the most obvious problem with auto-routing, the way you did it, is that
the power and ground traces are not nice and fat [ie, 30-50 mils], like they should
normally be to handle non-trivial currents.

So I should change the width to 50 mil and then click on each power and gnd trace?  Is there a quick way to change them all at one time?
130  Using Arduino / Project Guidance / Re: What's a Due do? on: December 29, 2012, 12:52:14 pm
Massimo Banzi gave a great introduction to it at Maker Faire NYC this year.  The entire talk is here:

131  Using Arduino / General Electronics / PCB Routing Tips? on: December 29, 2012, 12:37:07 pm
Well after much moving and re-jiggering of components, followed by vast amounts of wailing and gnashing of teeth, this is as good as I could get things in terms of a rats nest.  Is this normal or is there some trick to getting things to magically line up?


GPS_LOGGER by jg1996business, on Flickr

This is what it looks like after running the auto-router on it:


GPS_LOGGER_AUTO_ROUTE by jg1996business, on Flickr

Is it too ugly to work?
132  Using Arduino / Project Guidance / Re: Solder footprint question on: December 28, 2012, 10:31:50 pm
Nothing. It's just drafting style.

The (5) smaller lands are for the connections. The (6) larger lands are just for supports. Look at the mechanical drawings. 

(when you're pushing and pulling plugs, you don't want those (5) small lands to be the only thing holding your part on your PCB. They won't be able to take the stress. The bigger lands hold the part, i.e. welded to the PCB.)

Thanks!  That is what I thought but I wanted to be sure.
133  Using Arduino / Project Guidance / Re: Solder footprint question on: December 28, 2012, 10:31:24 pm
are you making a stencil so a machine can screen paste it?

No....just creating a new part for my Eagle library to use on my board.
134  Using Arduino / Project Guidance / Solder footprint question on: December 28, 2012, 09:37:51 pm
On this data sheet:

http://www.molex.com/pdm_docs/sd/473460001_sd.pdf

they show the recommended solder footprint for this part.  Is there any significance to the fact that the hashmarks on the 5 pin pads are going a different direction than the hashmarks on the 6 larger pads?
135  Using Arduino / Project Guidance / Re: Modifying the solder stop mask for a pad in eagle on: December 27, 2012, 09:17:59 pm
If you're asking to make the stop mask larger, then you would select the polygon tool, select the tStop layer, then draw the polygon so it overlaps the existing stop mask; the two will combine to create a larger area as you would expect. If you're trying to make a stop mask smaller then you would need to modify the IC package and remove the pad completely, then manually create the stop mask and pad using the polygon tool.

When your project is complete it's always a good idea to doublecheck the results using a Gerber viewer (like GerbV, etc.).

My goal is to make the stop mask smaller.  I read somewhere that the router will only work if you use the pre-made pads in eagle.  Is this incorrect?  I do have something worked out but I am not sure if it is the appropriate way to solve the problem.  The first picture below is the original part with .5mm pitch SMD's.  As you can see, the stop mask almost touches.  The second picture is one where I turned off the stop mask on the pad and then placed a new polygon on top of it with the correct dimensions and assigned it to the tStop layer.  Will this work?


big_tStop by jg1996business, on Flickr


small_tStop by jg1996business, on Flickr

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