PCBgogo

I must admit that I am aquiver with excitement about my project to create a pedagogical and phantasmagorical inamorata prognostication engine. Key decisions have been made, interesting developments have developed, and all sorts of things are coming together, as I shall discuss in a future column.

One slight issue: I have been unable to locate a suitable off-the-shelf prototyping shield for the Arduino Mega microcontroller I am using as the brains for my engine. Some time ago, when I was playing with my first Arduino Uno, I purchased an associated prototyping shield from Adafruit.

Adafruit Arduino Uno prototyping shield.

More recently, while perusing all the goodies on Adafruit.com (something that I seem to find myself doing on a daily basis at the moment), I saw a rather tasty Arduino Uno Proto-Screwshield. As you can see in the image below, it has blue screw block terminals around the periphery.

Adafruit Arduino Uno Proto-Screwshield.

As soon as I saw this, I thought, "Oooh, shiny. I want something like that for my Arduino Mega." You can only imagine how sad I was to discover that the only Arduino Mega prototyping shield available is the standard flavor shown below.

Adafruit Arduino Mega prototyping shield.

Fortunately, my chum Duane Benson can whip out a circuit design faster than you can say, "Wow, Max truly is magnificent." I called him up and explained the problem. He said he would look into it. the result is what I think of as a Bensonfruit Arduino Mega prototyping screwshield.

We did run into one slight gotcha. Duane uses EAGLE PCB for his hobby projects. There is a free version of EAGLE PCB, but you can’t use this for commercial projects. Duane uses EAGLE Light (one schematic sheet, two signal layers, 100x80mm routing area), which does allow him to sell the boards he creates if he chooses. The problem is that building a single large prototyping board suitable for an Arduino Mega would exceed the size limitations of EAGLE Light. We came up with what I think is a jolly clever solution, which is to split the prototyping board into two pieces, each of which will be implemented as a standalone entity as illustrated below.

Bensonfruit Arduino Mega prototyping screwshield

The cool thing about this solution is that the lefthand board will also work for an Arduino Uno. Also, I think we've come up with something rather clever. In some cases, I will want a header pin to be connected directly to its corresponding screw terminal block. In other cases, I will want to connect a header pin to components in the prototyping area, and I will want to connect components in the prototyping area to the screw terminal block associated with that header pin. Our solution appears below.

Close-up view of the Bensonfruit screwshield.

As we see, the first row of pads inside the header (as we move toward the inside of the board) are connected to their corresponding header pins. The pads in the next row are connected to the corresponding screw block terminals. If we wish to connect a header pin to its associated screw block terminal, all we need to do is insert a jumper between these two pads. Otherwise, we can use wires to connect these pads to components in the prototyping area.

I don't know about you, but I think this is jolly tasty. The next step is to send these off to a board shop to get a few of these boards fabricated. Duane says he uses two board shops for raw PCBs.