For a start, the shield available in Adafruit has a lot of thing we are not using, the USB port, The digital pinouts (pin header stackers), etc. We can also use SMD components instead of the classic through hole and let's talk about the memory, there is no need for a SD, we could implement a SPI memory and later get the data through a micro-USB cable, so let´s hands on.
For designing the PCB I'm using a software called "EagleCAD", the free version allows you to use only 2 layers and a limited area size. Though the area limitation may sound irritating it is not since we are looking for portability so... time to turn our disadvantages into advantages.
Once you have the design of your PCB you can send to produce your PCB to some fabric. Personally I use a fabric called Oshpark (oshpark.com). They give you a really good price and the product is really fair considering price vs quality. The only thing is that the only color they give you for your PCB is purple so if you are not a color-maniac or a green lover you should do it just fine.
Basically for the PCB I used a GPS, a tiny memory and a microcontroller, everything on its SMD package. But I am missing something huge, the shielding, for this I designed a little bicolor box where the whole circuit was held. It is pretty cute I must say! Then I printed it in shapeways.com and after 2 weeks I was able to test the prototype for the first time with professional soccer players.
In the picture above you can see 2 pictures. The first is the original sample I got from the soccer player, as you can see it is really noisy, the noise is due to GPS malfunctioning so most of this points are likely to point to some really distant places (some several miles away), in order to get rid of this noise is really simple, I only had to implement a condition, for every distance higher than 10 (33 feet) meters in less than a second, erase it and then just extrapole the missing spot with the next one, in other words, if your speed is over 36 kilometers per hour (22.5 miles per hour), there must be a mistake there (unless we only have Usain Bolt's in the team... NOT). In the right picture you can see the trajectory after the filter was applied. Sweet!
Finally I just replied the same device 2 more times and work ready. Today Magallanes F.C is using this device for evaluating their players and they are planning to build for devices in order to measure all of their players and track their activities. For me it was a very entertaining project, I had a lot of fun using different components and tuning their performance but I consider that the future of this project is not related to hardware anymore but software, that is Vision machine and Image processing. Who knows if the next world cup held in Russia gives us the opportunity to release a new technological improvement for sports.