Week 6: Electronics Design

How to make a new device on EAGLE

It then comes to EAGLE design.
Owing to the fact that on fab.lbr there's no device³ for Atmel XMEGA 16e5 I had to create one. When you have to do that, basically you have to open your library and add a package⁴ and a symbol⁵. In fact, each component on EAGLE is made of this two elements, linked together: the package is your real component (so you have to check on datasheet exact dimensions of pins, case etc) and pin function (to say it better, the name related to pins' function) is said in the symbol.

Package design

I started drawing a package because I still didn't know there's a standard one on fab.lbr that also suits Atmel XMEGA 16e5 features, but I learned that from the datasheet (I'll tell you where in picture below) soon so I stopped wasting time and patience in this precise but entertaining procedure.
I will briefly explain how I started, getting lots of help from these tutorials and websites:

• on Adafruit.it there are great tutorials about both symbol and package editors;
• in this article there's a global overview about components design;
• PACKAGE:
  • a goodvideo for new package design (I found pad design weak so I looked at the one below);
  • this video has no explanation but it's quite intuitive - despite causing seasickness a bit;
  • I also found useful tips on EAGLE Help website, especially for these commands:
    • GRID;
    • WIRE;
    • SMD
• SYMBOL:
  • nice tips about making a symbol complete and also about how to make a IC symbol here - but not enough if you haven't seen a symbol editor before;
  • Adafruit website, as said before, has great tutorials;

So, as I said, I started designing my XMEGA 16e5 package and I found this part very challenging, because you have to be careful in respecting your components dimension so as to have a realistic idea of size proportion among other board elements so that you draw a schematic most like the board you'll mill.
IMPORTANT!: find and analyze dimensions info on component's datasheet before drawing!!!
I found this technical drawings at page 68 of XMEGA 16e5 datasheet (PDF at the end of the page):
....Did you see those tiny words in the bottom of the picture?? Yes, dude, I didn't care about them at first just like you, but they matter quite a lot... Go back and read them, they'll be relevant in few steps
So, finally, we come to package design:
I went through File-->New..->Library to create a new library - this step isn't necessary, if you feel confident not to make a mess into fab.lbr you can just open it. I thenk clicked on Package symbol and create a new one After this operation (also for symbol editor) you will be asked to confirm your operation, click "Yes": The workspace becomes black with a grid: You can change grid features clicking on its symbol in the upper left part of workspace- I chose 1mm size: I then used WIRE command in the command line above workspace: As you can see, the formula looks like WIRE # (x₀ y₀)(x₁ y₁)(...) -where # stands for line thickness- and in XMEGA 16e5 case I used 7mm side square.
I then wanted to add pins to the microcontroller body so I clicked on SMD symbol and changed size in upper bar to make them suitable to my component (see datasheet and this file for my sketch dimensions). I then used SMD command to put pads in (that one I think was) the right position: After putting 8 of them in the left side, I saw there was an error: As you can see the upper first and last pin were shifted from edges with different quantities. I tried to repeat the same procedure two times and the third with half thickness of SMD but I still had same problems: I so started thinking there wasn't a reasonable reason why, to do this weekly assignment all the students should have improved fab.lbrwith more than 200 almost equal packages of XMEGA 16e5.
....Meditating...
Do you remember I said those tiny sentences matter quite a lot? That's because there's a sentence saying :
"This drawing is for general information only".
It made me think I was using dimensions (the ones in the table) that beside being discretionary (there's a minimum, nominal and maximum value you can use) didn't even correspond to real one. I searched for the document said to refer to but after five minutes of no results, it came to my mind that it was impossible that loads of programmers haven't never found a common design for XMEGA 16e5 device on EAGLE: so, after careful reading of datasheet (just parts close to drawings, to be honest, because 300 heavy pages were too much to be taken into consideration in just an afternoon) and I read that: What the evil those words meant? they're package format acronym of XMEGA 16e5 and you can also find it on fab library: NB: please note that this package seems to have too large pads and, while milling, they really come out too close together; it will be enough to edit .png file of traces exported from EAGLE before sending it to fab modules
The problem in the line above, made me think I would really like to design a suitable package for XMEGA 16e5 but it really takes a lot to do it precisely, so I preferred to follow .png editing way.

Symbol design

Since I had the package of XMEGA 16e5 but not its symbol, I created a new one clicking on Symbol button: To make my symbol, I just used these commands:

• Wire;
• Pin;
• Name;

Result: To give proper names to pin I referred to datasheet description: NB:

• please note that XMEGA 16e5 has two GND pins, so I gave them two different names "GND@1" and "GND@2", because typing "GND" for both gave an error;
• dimensions and proportions of real components aren't necessary in this step, the symbol can be as big as much you feel comfortable in positioning pins

Create a device

Now that I had both package and symbol, I had to make them communicate somehow.
In fab.lbr I pressed on Device button and added a new one: I then added the symbol I designed... ...and the standard package (by clicking on New in the bottom of the window on the right Then, by clicking on Connect -close to New- a new window helps you in associating pin and pads: NB: pay attention to this passage, give a look to datasheet pin number and care not to confuse pin names and numbers!

Schematic design

I was then ready for Eagle, so I opened it and went through File-->New..->Project. NB:I already had fab.lbr installed (see above "EAGLE 7.7.0: import libraries and examples" if needed)
My project appeared on the left column of the workspace and I opened a new schematic inside it (left click on project name then right click and New..->Schematic). Using the ADD symbol you can put components on the workspace: Repeat this for all components: Then you have to link pins of different components; to make it easier, start from hello board .png file: Commands to be used are:

• NET: that creates link;
• NAME: that assign a name to the link;
• LABEL: that shows link name in a label;
• VALUES: for optional definition of quantities and units of measurements (see R2 resistor in my case).

2.3 Board design

Here I found a good tutorial to get started.
I advice you to double-check connection and just after that switch to board visualization (now connections will be displayed with yellow lines) Yellow lines have to be switched to traces that can be drawn with ROUTE command. NB: If after routing, you still notice yellow lines, like this... ...check red lines really snapped to pins.
Then it comes to DRC rules: in this part you can set routes characteristics to suit endmill dimensions (you can set them before or after routing) I changed Clearance and Size properties: To check if your routing suits DRC rules go through Tools-->DRC and click Check in new window. Errors will be displayed with red lines.
TIP: when you have several lines to pass in a strict path, changing grid can helps you in tiny movements. Also, press Alt button while moving will gave you a precise drag and drop.

Using GIMP to edit a board .png

Once I had .png file I had to make them ready for fabmodules. There's simple process to follow on GIMP:

• open image;
• right click: Image-> Autocrop Image;
• right click: Image-> Canvas Size;
• in window opened, add 100 px per each dimension and click on Center;
• right click in Layer window on the right: New Layer..-> Foreground color;
• drag and drop new layer under the starting one;
• right click in Layer window on the right: New Layer..-> White;
• right click on the image: Select-> All;
• right click on the image: Select-> Shrink and set 20px shrink;
• right click on the image: Select-> Invert - check a border is flashing;
• go through Tools--> Paint tools-> Bucket fill and set black color;
• fill in the flashing border with black;
• export first traces and black layer (hide white layer): this will be traces .png file;
• export white and black layer (hide traces layer): this will be outline .png file;

NB:I still have a doubt about outline .png file: should it be white bordered with black inside or the other way up? Until now, I have proofs to say outline milling works in both ways ( because in week4 I used black filling while I had the best result of hello board using white infill). Theoretically, Roland SRM-20 mills what in black and leaves what in white but I will try to make more experiments to discover best case to use. In any case for black and white drawing it doesn't matter a lot since on fabmodules there's an option to invert colors.

Below, screenshots of GIMP procedure:

White border and black infill:

Black border and white infill:

PCB milling

For milling procedure see week 4.