Symbol based modules

Posted by Joe George at

The process of designing a board involves three steps. First, a schematic symbol and PCB footprint are designed for each part that is to be used. Second, a schematic is drawn which includes each of the symbols and how they are connected together. Third, the board is designed with the each of the footprints placed and the connections routed. Each of these steps has an associated file type. The schematic symbols and PCB footprints are contained in one or more library files (.lbr). The schematic is a single file (.sch) consisting of one or more sheets. And finally the actual PCB layout is contained in a single file (.brd). To manufacture a board a Computer Aided Manufacturing (CAM) step is done to convert the layout into industry standard Gerber files that can be sent to a board vendor for the fabrication.

During a recent project we developed a python program that takes a schematic and a board file and generates a symbol for a module based on the design.

This is a picture of the top of a module implementing a Spartan 6 FPGA.

This shows the back of the FPGA module whch has four 60 pin connectors which allow the module to plug onto another board as shown below.

The board the modules plugged on to holds 5 FPGA modules plus 89 other modules. So our python program creates a schematic symbol for each module type and a PCB footprint for the mating connectors and silk screen outline that you see in the above photo.

This system allowed us to design and build a very complex system board. The system was very densely packed and if it were not done in this modular way it would have been exceedingly expensive. One of the big benefits was that each of the modules could be tested individually. This was especially important for a complex analog amplifier module of which there were 81 in the system.

Engimusing is designing general purpose modules that will use this development method allowing compact devices to be built.

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