Friday, March 28, 2014

A PCB for the K9 Dorsal Keyboard Driver

So, I mentioned that the driver board for controlling the dorsal keyboard panel shorted out on me. Well, I have decided to not rebuild it from a prototyping board but instead get a printed circuit board manufactured so this does not happen again. This way there is no chance of a home mead header pin folding over as the traces should be sealed and I will be using a real head block this time like the kind present on the Arduino.
I have only ever built home made printed circuit boards before. I have never used CAD software to create them and I have never designed a multi layer board before so this was quite an education. Here is a little bit about what I learned.

Seedstudio will manufacture five copies of a 2 layer 5x5cm board for around $10 by sending it out to China. I am in no hurry and this is a great price. Element 14 recommended  Sunstone Circuits who can do a single prototype for $40 and get it to you faster.

All of these manufacturing houses require something called Gerber Files which it turns out have nothing to do with baby food at all but are actually a set of documents that describe the layers of your board such as the silk screen, top layer, bottom layer, connections between layers (called vias) and where holes need to be drilled.

I needed a way to create these files and I discovered a free to use CAD program that will help you lay them our called Eagle. Eagle is not as simple to use as a lot of modern drawing software and harkens back to old unix workstation engineering packages a little bit but there are a great set of tutorials on how to use it by Jeremy Blum. This was pretty much all I needed to create the PCB board design shown above.

This board was pretty simple to design since all I really had to do was draw out the entire circuit diagram. 

From this, it created a sample PCB and I moved the components to where I wanted them to be located. Since this board does not carry any high frequency signals I did not really have to worry about shielding or bends in the tracing but the tutorial addresses these issues as well.  Next, it auto routed two layers of copper for me and then let me tweak the routes and add my own text to the silk screen layer. With the help of Jeremy's videos I rendered the gerber files and am about to place my order with Seedstudio. When the boards show up, I will talk more about how well the whole processes turned out.

I have placed my eagle project on git hub.

1 comment:

Nick Beinhoff said...

I am building a similar K-9. Two mods you might be interested in is a snoopy-ng interface, http://www.sensepost.com/blog/10754.html and I am putting in a SDR for the tail.