Sunday, January 17, 2010

Project #1 - electronic CAD

To make a simple PCB by etching, I don't need any software, or special equipment - just some good chemical solvent (for cleaning the copper) and permanent marker (for drawing connections). But it's extremely hard to make anything more complicated that way - it's a medieval-book-writing-monk type of work.

Using specialist CAD software helps a great deal. What does PCB CAD essentially do? It connects the logical design of the circuit with physical design of the PCB. First I make an electronic schematic of my circuit - using logical symbols like resistors, capacitors, ICs and connectors. Every time I need to use a part I open part database, choose a suitable element, and place its symbol onto the schematic. Then I connect the parts using wires (lines). When I'm done, I click "PCB Design", and the program opens another window, where once again I place symbols of my components. But this time I place physical parts - with proper dimensions, pinouts and packages - the program automatically assigns physical symbol to every logical symbol. After that I route wires between the symbols and it's done. Optionally I may generate CAM files used to manufacture my PCB on CNC machine.

There are many free PCB CAD programs on the web. These are often connected to some big part suppliers. This is probably the most complete list available. For my project I chose a program called Eagle by German company CADSoft. It's free for hobbyists, and has some limitations, but they are not important in small projects. Eagle was fully independent software some time ago, but it has been purchased by Farnell - big part supplier. I expect some new version of Eagle with integrated Farnell part base to appear. However Farnell is quite expensive when buying small quantities of parts (ex. single ICs), so a hobbyist like myself won't be using this kind of integration much. It's quite sad, because integrated part base would make my life much easier. Maybe in a country like US people may put any part they want into their projects, but here in PL I have to carefully check availability of every part. Otherwise I'll either wait 2 months to get it, or pay 2 times the price, sometimes both.

About Eagle - it has some pros and cons - I'll describe them briefly:
(+)
  • Has decent database (I usually find what I'm looking for) and user-made libraries
  • Easy to use (it has a command line for hard-core users)
  • Many resources on the web
(-)
  • Pathethic database searching (it's 2010 now, everybody has autocompletion and search-as-you-type in their programs, and here I have to type name in little window and press Enter)
  • Shortcut - not Windows compatible
  • Tediousness - for example as a hobbyist I want electrical pads in my projects a bit larger than default - I don't know how to achieve it without modifying every single symbol

With this post I finished the introduction to my project. The information contained here is obvious for most people, but I felt that it's necessary to describe it, as it's part of the project too. With the next post I hope to move on to some technical details.

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