Building a Magnet Matrix

I did many tests with the Outmoded Sequencer how to use steel balls as switches. While this is working very well from the electronic point of view, one problem was the steel balls tended to fall of the PCB easily and roll under furniture.

To hold the small steel balls into place I am building a matrix of 8×8 neodym magnets. This magnet matrix is later mounted below the PCB, so there will be one magnet for each pad on top.

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I am using these small, but very powerful neodym magnets. They have a diameter of 4 mm and a length of 5 mm. You can get this magnets, any many other shapes, from Supermagnete, they deliver the magnets to almost all European countries.

I started by using the holes in the PCB as a template to put marks onto a piece of plywood. Best is using a stitching awl, to create small holes. Next I drilled 64 holes with a diameter of 4 mm into the plywood.

To fasten the magnets I glued a thin paper on one side of the plywood and put a small amount of glue into each hole from the other side. Then I placed one magnet in each hole.

This is very difficult, because this magnets are really strong and you have to keep them from leaving their holes and stick together. If the holes are precise made, the magnets can not move easily which prevents them from popping out of the holes.

Next I added a thick layer of black acrylic paint on the wood and magnets from the other side. Dry acrylic paint gets very tough and will stop the magnets moving around.

I let everything dry for 24 hours, then cut plywood to the final size. I used an utility knife to do this.

Now I added another layer of black acrylic paint. I also painted the other side of the magnet matrix which will be visible trough the holes of the PCB.

In the next step, I will bring the PCB of the outmoded sequencer into the right shape, by drilling the final holes into it. After this I just have to assemble and test everything.