Sunday 8 February 2015

EAGLE - PCB design software

Eagle is not the easiest software to understand. But I have invested a number of hours to get to grips with it. This is what I have found. (This tutorial was written using the "Lite" version of the software from the Cadsoft web site £60).

This blogpost will cover the starting point for creating Devices to use in your designs if you can't find them in an existing library. A future post will cover drawing a schematic and generating the PCB layout. You could also check out this or this site.

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Eagle

Eagle handles these levels, in descending order:

- PCB Design

- Devices or components

- Packages used on PCB layouts

- Symbols use on schematic drawings

- Gates, which are fundamental building blocks of devices (e.g. the individual op-amps in a quad op-amp device)

Libraries and the Device Editor

There are a myriad of libraries of devices from many suppliers, and your software comes with a lot of them, plus many others are made by users for devices they need. There are some web sites, for example this one, to help find if a device exists in a library somewhere.

I would recommend that you chose the libraries you need for your projects, then move all the other unwanted ones to a "oldlibs" folder. This make design a lot easier.

Often you may want to create new devices that you can't find. So here's how to do it using the Device Editor.

Definitions

Device - a combination of a symbol and a package. So that a symbol used on a schematic diagram can be directly translated to a physical device for the PCB layout.

Package - which is the outline and connection types and positions (e.g. SMD or thru hole)

Symbol - the device schematic graphic, and pins to which connections can be made

Gate - parts of a symbol if they are repeated in one device.

When Eagle is started this is the window that appears, called the Control Panel.

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There are two important items on the left, Libraries and Projects. under the Library list are all the libraries that you have installed in your /lbr folder, under /Eagle. Under the Projects list are the designs you have made or are working on.

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Libraries and new devices

If you can't find the component you need in existing libraries , you will have to design a Device. First create a new library for your components.

- Control Panel, File > New > Library

- Library > Description, enter a description of your library

- File > Save As...

With the Library open you will have this window

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At the top are three important icons, Device, Package and Symbol.

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Making a new device

Start at the level of Gate, creating one of the internal parts of your device.

Symbol

- Chose Symbol icon, then File > New... and name it

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In the editor window draw the device and the pins.

- Make an outline of the internal gate, Draw > Wire

- Add pins, Draw > Pins

- Name the pins, View > Info, like the component data sheet

- Set pin direction, Edit > Info > Direction and the pin visibility, Edit > Info Visible (note: chose "pin" to have only the pin name showing on the symbol/schematic)

- Add text, Draw > Text... ">NAME" and ">VALUE", and put these on the 95Names layer, Edit > Info... Layer 95Names

That completes the gate creation. File > Save.

Package

- Chose the package icon, then File > New... to name it

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- Set the grid "on" at a suitable resolution for the physical package design, see data sheet

- Draw the pads, Draw > Pads (either SMD and set size) or Pins (thru hole and set shape) and position them correctly

- Draw the outline, Draw > Wire, then Edit > Info to change the lines to the 21Place layer.

Device

Chose the Device icon, then File > New.. and name it

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- Add the gate(s) to the left hand pane, Edit > Add

- Rename the gates "A","B", etc Edit > Name

- Set the gate levels to "next", Edit > Info

Add a power supply connection if this is not one of the pins, this will provide a hidden connection to VCC & GND.

- Edit > Add "PWRN", right click PWRN symbol and set Add Level to "request" (Note: it will then not appear on the schematic, but the signals will connect)

- Add the package in the top right pane, New button... chose package

- "Connect" and chose correct pins and pads to be connected

- Set a naming Prefix, e.g "IC", "T", etc (Note: devices on the schematic will be names IC1, IC2 etc)

File > Save All

Additional help

It maybe that someone else has already drawn the package and a similar symbol to the device you are creating. You can use their Package and symbol drawing in your Device like this:

- Control Panel, open libraries. Right click on the library containing the Device with the Package and/or Symbol you want to copy.

- Open the Package or Symbol

- Edit > Group and drag a box round all of the Package or Symbol

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This will high-light the selection:

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- Edit > Copy

- Now open your Library, chose your Device. Open its Package and or Symbol and Edit > Paste

That's it.

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