Advanced Eagle Layout Tutorial - Building Better Library Parts - Variants and Technologies

Advanced Variants

Everybody knows that to create a device set you must have at least one variant of the device that binds the symbol to the package. The default variant is called ''. That is right. Double single quotes. It represents an empty string.

Naming Variants

You may have also noticed that if you name a variant, the name is appended to the device name. For example, if you have a device named

WIDGET

and a variant

123

the resulting name will appear as

WIDGET123

Pretty cool, huh? Often manufacturers will have a package code embedded in the device part number. For example, if

WIDGET-

is the base part number, and the manufacturer has package codes

S

Dirt Cheap USBasp AVR Programmer Available

Did you know that you can get a super cheap USBasp AVR programmer? $4.95 plus shipping (around $3 for International Unregistered). Where can I get this you might ask? An unlikely source, HobbyKing.com. Wow. I don't know of anywhere else that can sell it that cheap. Generally stuff takes at least one month to arrive to the US from China, that is if the item is in stock. Longer for backordered items. But that is super cheap! Next HobbyKing order I make I'll through one on and review the programmer.

Eagle's Library Part Creation Standard

Did you know that Eagle had a Library Part Creation Standard? I didn't either. Check it out. I've seen plenty of parts that violate some of these rules, and consequently make life a little more difficult.

Advanced Eagle Layout Tutorial - Building Better Library Parts - Pin Swaplevel

Once you have pin direction down, we can move on to some of the other features of Eagle's pins.

How to Use Pinswap/Swaplevel

Swaplevel can come in handy on occasion. Its purpose is to allow you to be able to dynamically change which pin is assigned to a certain pad when using an instance of a part in your schematic/on your board. The end effect would be the same as physically swapping the pins' locations in the symbol while leaving the rest of the symbol intact. Let's look at an example using a simple resistor:

Now, because a resistor is the same forwards, backwards, and and any which way, it makes sense to be able to arbitrarily swap the pins. Look at the following board.

Oops, my nice row of resistors has one that is flipped! I could rotate the part 180 degrees, but then the text name would in the wrong place. I can simply select the 'Pinswap' tool, click on the first SMD pad and then the second. Voila! The pins have been swapped!

Advanced Eagle Layout Tutorial - Building Better Library Parts - Pin Directions

CadSoft Eagle is a great tool. However, I've only ever come across basic tutorials to get you started. A lot of features of Eagle are buried in the help files. These tips should help you become a power Eagle user and take advantage of a lot of things that eagle can do.

I assume the reader has basic familiarity with Eagle, and has a basic understanding of PCB design. I will explain some of the more advanced features of Eagle

First up, Pin Direction

Let us start in a symbol for a device.

When you add pins to a symbol, there are several options for the pin. Most of the options are aesthetic, but some come in handy when you run ERC. If you look in Eagle's help file under the 'PIN' command you can find this little blurb.

The Help

Direction
The logical direction of signal flow. It is essential for the Electrical Rule Check (ERC) and for the automatic wiring of the power supply pins. The following possibilities may be used: 

NC - not connected
In - input
Out - output (totem-pole)
IO - in/output (bidirectional)
OC - open collector or open drain
Hiz - high impedance output (e.g. 3-state)
Pas - passive (for resistors, capacitors etc.)
Pwr - power input pin (Vcc, Gnd, Vss, Vdd, etc.)
Sup - general supply pin (e.g. for ground symbol)

Default: IO 
If Pwr pins are used on a symbol and a corresponding Sup pin exists on the schematic, nets are connected automatically. The Sup pin is not used for components. 

Graphics Cards Hacking (Repair) Roundup

I must have bad luck with graphics cards. My last graphics card was an XFX nVidia 8600GT. My current graphics card is an EVGA nVidia 9800GT. Both have failed in unexpected ways. Fortunately, I have been able to fix both of them! WARNING - these procedures will most like void the warranty, if you have one.

XFX 8600GT

Exploding Caps

One evening I was sitting watching TV in another room with my wife. We heard some 'pop' noises. Well, more like several loud 'cracks'. My wife asked me what the sound was. I thought it was the ice maker in our fridge. Suspiciously, though, the graphics on my computer started having problems. I began seeing artifacts here and there. Then, more pops and the display become incredibly garbled and unusable. I pulled out the graphics card and what you see above is what faced me. Numerous aluminum electrolytic capacitors had exploded. You can see the paper separator(the yellow fibrous stuff) spewing out.

The Fix

To fix the 8600, I purchased some aluminum electrolytic capacitors from Digikey with the same values as the exploded ones. Generally, caps that large have their values and ratings printed on them. I needed some 1500uF 6.3V, 1000uF 6.3V, and 470uF 16V capacitors. The footprints for the capacitors were generic and supported multiple sizes, so I just got the cheapest ones in approximately the same size. Radial capacitors have 3 dimensions to consider. Lead spacing, diameter, and height. In retrospect, the replacement 1500uF caps are a lot taller than the original, but they still fit in my case. I wouldn't worry about stressing too much about matching ESR or any other features other than capacitance and voltage rating. Odds are that the originals are on the cheaper side.