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The Hardware Saga Continues... | Print |
Written by Akiba   
Tuesday, 14 July 2009

Well, I warned everyone that the FreakZ project is now entering a hardware phase so don't be surprised if you hear about hardware for the next couple of weeks ;)

Anyways, I got the MCU board up and running and everything was working as it should. It actually came up very quickly because it's the same MCU as the Raven boards. Hence the MCU initialization and the USB interface is mostly the same. After I verified the MCU was okay, then I started working on getting a radio board to match it up with. The first radio board will be using the AT86RF230 of course. It's the same radio as the Atmel Ravens and will serve as a good reality check. In case there's anything wrong with my system, I can always compare it to the Raven since the hardware is essentially the same. 

I spent most of the weekend working with my CNC machine to optimize its settings. It's been about six months since I last used it, and back then, I felt really rushed to get things up and running so I could get back to the project. This time, I decided to spend more time with it and really learn how to use it well. It's like an instrument, where it can do what you want it to do, but only if you know how to use it correctly. So I was trying out different bits like V-cutters at 30, 45, 60, and 90 degrees and different size end mills. I finally settled on some tools that worked out well for me and gave me the best results.

The CNC software was also recently upgraded, and I purchased the Pro version of the software which will allow me to cut solder paste masks and import DXF (CAD) files. This is going to come in really handy since I'll be making a lot of boards soon, both for the Tokyo Hackerspace as well as the FreakZ project. The CAD import is a nice feature because I can design front panels and mill them in my machine. Previously, the CNC's software could only handle PCBs and some simple engraving. 

After I got familiar with the new software and tried out a bunch of features, I decided to rig some tooling for the CNC to help in aligning my work pieces so that both top and bottom layers align correctly when you need to flip the work piece over. One big issue with people that do homebrew PCBs using etching is that it's very difficult to align top and bottom layers. With the CNC, I could precisely drill registration holes that I could use to align the PCBs and they would be accurate to within a couple hundred microns. 

So anyways, that's pretty much why I've been quiet recently. Although it's great to learn how to use the CNC efficiently, it's just not interesting enough to blog about. Or at least I don't think that people that follow this blog would be interested in me comparing annular ring sizes with respect to different drill bits. 

Well, that's about it. I left out all the boring details and thought I'd just post a couple pics of the finished radio board. It seems like every PCB I'm posting lately has no solder mask. With RF components being 0402 are smaller, soldering them down is a real bitch. The worst was the balun which is basically an array of 0201 components. While I was squinting and trying to attach it to the board, I kept on thinking how I'd be better off trying to solder individual specks of coffee grounds to the damn thing...

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written by Kevin, July 14, 2009
That seriously couldn't have been fun to solder. smilies/wink.gif Unless I really need something right away, I rarely use my CNC Mill for PCBs simply because it's just so much easier with the solder mask on a commercially made board. If I can figure out the magic formula to get my mill to cut solder paste stencils, though, I think it will see pretty steady use. The problem is that my spindle is way too high speed to cut through a lot of metals, even soft ones like brass, copper or aluminum. It's fine for removing a very fine layer of copper like on FR4, but to actually cut through 0.10" of aluminum it seems I really need to slow it down a lot. The V-bits don't seem great for this either, and you need a real endmill, but at 0.20mm they're both expensive and very fragile. smilies/sad.gif

Kevin.
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written by Akiba, July 18, 2009
Actually, I keep my spindle speed at 60,000 rpm and use a 7-mil stub end mill to carve the traces and pads. It seems to work quite well at that high of a speed. If you use it on acrylic, though, it's gonna melt and stick to the bit.
The toughest part is the soldering, but with so much practice recently, I'm getting a much better intuition for how to approach tough areas.
I also much prefer commercial boards with a solder mask since they're soooo much easier to work with. However when you're doing RF, a lot of unknowns can suddenly jump out at you. For Zigbee/802.15.4, it's lucky that you're not working on wideband frequencies and can just focus on 2400-2500 MHz. However simulators and calculations are never enough. A lot of trial and error is involved if you want to get good impedance matching (ie: high (negative) return loss values).
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