2017-05-12 (F) Weekly Summary

The first design for the tagger circuit was completed in KiCAD and printed on paper to make sure scaling was done properly. Sure enough, the paper lined up perfectly with the actual pins of an Arduino.

 Arduino on a paper printout of the circuit

While holding the paper printout, it became obvious this would not fit inside the tagger. In retrospect, the stripboard built days ago would probably not have fit either. The shape of the board would have to be reevaluated.

Paper circuit board held near pipe

In KiCAD, every time the circuit layout needed a major revision, like resizing the board, everything needed to be reconnected. This was a time-consuming process and in most PCB designing programs it has been automated by an autorouter. KiCAD used to have one but it doesn't come standard right now. The simple circuit was instead rebuilt in EasyEDA, a free web-based PCB designer.

Tagger circuit built in EasyEDA

EasyEDA had an autorouter so making changes to the layout was faster than using KiCAD. The animation below shows an autorouted circuit which was designed with almost no regards to placement or optimization but that really exemplifies the power of an autorouter to make a good circuit based on a lazy layout.

EasyEDA's autorouted circuit

For the last five years I have not owned a paper printer, and for two years I have only owned a 3D printer. For this project, I bought a laser printer because they're well-suited to making prototype circuit boards. A printout of the circuit board proved that it would have little trouble fitting into the tagger pipe.

Paper circuit printout in the tagger tube

Special toner transfer paper was used in the printer to print a mirror image of the circuit then a clothing iron was used as a heat source to transfer the toner to the copper. There are lots of good instructions on the web for this sort of thing so I won't go into detail here. The transfer was not perfect and some of the toner can still be seen on the transfer paper.

Incomplete transfer

More problems with the transfer were investigated with a magnifier. While the picture above looks pretty good, a larger view shows that the trace lines are not intact and wavering can even be seen on the pads. The board doesn't appear copper-colored because of the automatic adjustments of the camera but it is the same board pictured above.

Magnified view of the transfer

Sensor boards, for detecting hits on a vest or hat, were designed as well. These were much smaller and simpler circuits. Fortunatey, when making boards like these, it's easy to dismiss a couple ruined boards as long as the majority of them survive. They were also made in EasyEDA.

Sensor boards on toner paper

The technique used to transfer the toner was revised. One of the problems with broken traces seemed to come from when the paper was cooling and it would crinkle, which broke the toner traces. For this reason, the board was clamped while it cooled.

Clamping the cooling circuit board


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