KiCAD footprints

Following on from the post about designing stripboards and the one about DesignSpark, I decided to try and create some wire footprints for KiCad.

In Design Spark Mechanical, I set the grid to 2.54mm and then I drew a couple of 1mm circles on the x-y plane. To that, I added an axis through the centre of each and then a new plane based on the axis. On this new plane, I drew a line up, across and back down to the second circle. The corners were rounded. The circuit could then be pulled/swept along the line.

Finally a cylinder was added to represent the insulation.

Then the next step was to save the file as a “Step” file, a common interchange file format. However, DesignSpark only supports this if you buy an exchange module for £415.

There do seem to be converter programs such as CADExchanger that will convert for example OBJ to STEP files. But at this point I needed another option.

FreeCAD

FreeCAD is the CAD software frequently used with KiCAD and hence it does support the STEP file format required by KiCAD 3D models. My initial view of the software was that I just seemed to be clicking on things and nothing was happening. But after watching a couple of tutorials I eventually produced a sketch for my wire and a path to sweep it along. Then after a bit of struggling, I added a datum plane to the wire and offset it by 0.5mm. That allowed me to create another sketch for the sleeve.

Parameters

The next step after creating the basic model was to turn it into a parameterised model. This allowed me to quickly export different lengths of wire without needing to make lots of adjustments.

When I was exporting I found that the wire came out as a single material so I first had to split the wire into 2 parts and re-do the sleeving in the new part. That allowed me to assign different materials to the wire and sleeve.

I added a length constraint to the wire sketch and used a formula to make it multiples of 2.54mm. I called this WireLength. The bend radius was fixed at 1.25mm and I mirrored that onto the other end. I then made the plastic sleeving length calculated from the other details. The DatumPlane offset is the distance between the end of the curve and the start of the plastic. As this is already negative the wire it is added rather than subtracted in the formula.

KiCAD Library

To import this into KiCAD I create a new library and then added parts for each of the wire types. For the footprint on the board, I simply added two pads. The 3D models that had been previously generated were then assigned.

The finished results came out pretty well but you’ll have to wait till the magazine comes out to see the results in all their glory.

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