HOW-TO: Create parts with separate power pins

in how-to by DP | 1 comment

Ever wonder how some designs group all the power supply pins in one corner of the schematic? They look organized, and it’s easier to understand how the circuit works because pins are grouped by function. In this tutorial we’ll show you how to make an Eagle part with separate power pins. This can be extended to group pins by function as well.

Create a symbol

Create a symbol for the part, we’ll use a 74LVC245A buffer IC. Save the symbol, we save it as “74LVC245A”.

Next, create a second symbol for the Vdd and Vss pins and save it. Lets name it “Supply”

Create a footprint

Create a package. This chip has an SOIC-20 footprint. We save it as “SOIC-20”.

Create a device

Create a new device. Add the “74LVC245A” and the “supply” symbols we’ve made.

Load the footprint “SOIC-20” after that.

We name the supply symbol “SUPPLY” and the 74LVC245A “IC” so it is clear which we’re connecting in the next step.

And finally the fun part, connecting the symbols to the footprint’s pins.

Add Level

When you’re new to Eagle separate power supply pins can be confusing. You may add a part to your schematic, but the supply pins are not included. So where are they? This is the ”Add Level” property at work.

Click on the pin and choose properties.  Set the ”Add level” property for the supply pin to “Request”.

Now the supply pins will not be displayed until you “invoke” them by choosing the  invoke tool in Eagle and clicking the part. Now the hidden supply pins are added to the schematic, and you can connect the supply pins to their corresponding sources.

See Eagle’s help for more ”Add level” parameters.

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Comments

  1. Andrew says:

    I think when you go to layout this can be somewhat more confusing. It’s nice to see what particular decoupling caps (especially if they are not all the same value) correspond to which particular part. It’s just more similar to how the board is laid out. Don’t get me wrong, this method has its advantages, but there are advantages to keeping power pins on the main component symbol.

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