Some important aspects of PCB layout

christmas-small.JPG

About four years ago, click when I first started using the Orcad suite, patient I embarked on an ambitious project to design one of my first EEG recording amplifier and stimulator interface boards. The project was pretty simple: route twelve differential channels from the pre-amp to the EEG amplifier, track the current going out of the stimulator by way of sense resistors and interface with a National Instruments acquisition board. I did the schematic entry correctly, but I neglected to double check the footprints used for the connectors. That is, in the schematic entry, I used a generic 68 pin connector for the NI connector and selected metal can regulators instead of TO-220 and then picked the wrong polarity on all of the d-sub connectors. The result was that the 68 pin connector just didn’t fit and required massive jumpering for even basic functionality, some of the db25 connectors had to go to the back  of the board (not shown) and the power regulators had to be kludged on. The board was not becoming a truly three-dimensional object that had wires coming out from every direction and could only be secured by clamping one edge of it in a vice. Otherwise, it functioned fairly well so it was still used in some experiments. Due to its green color and protruding wires, it became known as the “christmas tree” and be came synonymous with design failure.

christmas-tree01.jpg christmas-tree02.jpg

One thought on “Some important aspects of PCB layout

  1. Pingback: μblog: engineering from the trenches » Some notes on “Feature Creep”

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>