PCB is a printed circuit board design program that was written by Thomas Nau from the University of Ulm in Germany. The program is currently being maintained by Harry Eaton at the Johns Hopkins University Applied Physics Laboratory. PCB is distributed under the GNU General Public License (GPL). This article will demonstrate the use of PCB by making a circuit board from the microphone preamp circuit shown in the LWN feature article on Xcircuit . Pcb allows you to produce custom prototype quality circuit boards in a few hours with inexpensive equipment. Short development cycles have previously been restricted to the domain of software projects. Hardware designers can now benefit from improved, if still somewhat slow, cycle times.
Installation
To install PCB on your system, download the gzipped source code file, (Netscape users should press shift before clicking), and compile the program. The following steps were performed on a Red Hat 6.2 system with all packages installed: $tar -xzvf pcb-wip.tgz $cd pcb-1.7 $xmkmf -a $make become root and install the program: #make install Exit the root shell and run the program: #exit $rehash $pcb
A complete manual and reference card written in PostScript are included in the doc directory. To view the manual, either print the files on a PostScript printer or run gv on the file to view it on the screen. PCB currently has no included man pages.
Working with PCB
NetLists
The first step in the process of making a PC board layout involves creating a netlist file. A netlist file describes how the individual components are connected together. Node names are on the left side of the netlist file and are arbitrarily named. Part names and pin numbers follow on the right. A node is simply a point in the circuit where part pins connect. For simpler circuits, it is possible to skip the netlist stage and enter the parts free-hand. A netlist file may be created manually with a text editor or output from a schematic capture program. The netlist file should be created and pulled into PCB with the "file" menu and the "load netlist file" selection. Once the netlist file is loaded, corresponding parts should be pulled in from the parts libraries and named. To access library parts, click on the "window" button at the top of the screen and select "library". Click on the appropriate section on the left side of the library window and double-click the desired part on the right side of the window. The part should be moved to the main window and placed with a single click. The parts should be given the same names they have in the netlist file. To name parts, place the cross hairs over the desired part, type 'n', and type in the element name.
Rat's Nest
A rat's nest diagram shows which pins are connect together. Connection lines are drawn with the shortest possible path, so the appearence is somewhat jumbled looking, hence the name. After you have labeled all of the parts and loaded the netlist file, plot a rat's nest diagram by typing 'w'. The rat's nest can be erased with 'e'. At this stage, parts should be moved around the page and rotated to minimize line crossings. The rat's nest should be created and erased often during this part of the process. If there are problems with the netlist file or parts are missing, the rat's nest operation will pop up useful diagnostic messages. |
