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2009-09-11 Status Update + Going to California | Print |
Written by Akiba   
Friday, 11 September 2009

Well, it's only been about a month and a half since I took some time off from the software tasks to work on making a stable platform for myself. I have to say that it was a lot tougher than I expected. Actually within that time, I also worked on the webshop beta site, getting the administrative things out of the way (ie: registering a merchant account for credit card handling, choosing and ordering inventory, etc), and working on bringing up the Tokyo Hackerspace now that we've secured a house. Yep, things were mighty busy for the past couple of weeks.

It feels like forever since I touched the stack, and it's weird that I call this an open source software project because it feels like all I've been doing recently is hardware. However I feel like I'm building up a good infrastructure for the project's future. I think the difficult thing about open source embedded projects is getting a stable platform to develop on. It's one of the big differences between a regular open source project where you just develop software for a PC and it adds a lot of complication to things. For wireless sensor networks, it's even more critical because there are so many system constraints that you're dealing with: power management, MCU + resources (RAM/flash, IO, peripherals), radios, and antennas.

I guess I'm probably trying to justify the investment in time and effort for coming up with the hardware, but I do think that it's very important. I figure I'm going to be using the dev platform a lot to take things to the next stage, which is actual implementation. There are a couple of good platforms already available, but they're not exactly great for setting up a wireless sensor network. The platforms that are targeted directly at wireless sensor network development are also on the expensive side so I wouldn't be able to justify spending the money to purchase ten of them. And the worst part is that the platforms are fixed so you just need to take what you get with them. I'm hoping to be able to interchange power supplies, MCUs, radios, and antennas so that I can quickly prototype a platform to suit a specific need. 

But enough about that. I won't know how it goes until I get to actual testing, but I can say that I'll be back to working on software soon. The hardware has already arrived and I assembled the first batch. I did the first group of PCBs by hand because I like to work intimately with new boards. It gives you a good feel for any problems or errors that might have been made. Most people just think about functionality but there are a lot of things that can go wrong when fabbing a PCB. Seemingly simple things like having a pads of a footprint off by a couple of mils could turn into a manufacturing nightmare. Or you often find little things that might have gotten missed during the final check like a misaligned silkscreen, a reference designator that's hidden, and so on. That's why I think it's good to perform initial hand placement so you can get a feel for all the nasties that could turn up and bite you. 

Unfortunately, I won't be able to test the boards immediately because I'm headed to California tomorrow. It's a combination of work for my part-time job and also a chance to visit my parents and sister. I'll be up in Berkeley next week for a couple of days, then shuffling on down to Southern California to care of business. While I'm there, I'm probably going to be placing massive orders with Digikey and other US-based suppliers since the shipping is sooooo much cheaper. Everyone in the US doesn't realize how spoiled they are by not having to deal with international shipping. Also, Digikey won't ship any parts with embedded encryption outside of the US. This of course pertains to most 802.15.4 discrete radios and some MCUs I'm interested in, now that Travis Goodspeed has basically obsoleted an encryption engine integrated onto a radio. If anyone from TI is reading this, please send me a contact to order TI radios in Japan. I can't get them through Digikey and the local distis don't even acknowledge my existence. Apparently, open source projects don't get a lot of respect here :/

Other than that, I have to say that things are going quite well for me recently. I'm surrounded by PCBs, development boards, and really cool parts, hanging out with a really great bunch of geeks, and I'm finding Twitter extremely fascinating. Couldn't ask for more...

Here's a couple of pics of me unboxing the WSN dev platform I designed and assembling the MCU and radio boards. The explanations are in the captions:

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Solder stencil
written by Michael, September 12, 2009
Did you use your cnc machine to make your own solder stencils, or did you get it from your pcb house?
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written by Akiba, September 12, 2009
I'm cutting the stencils on the CNC machine using 0.1 mm copper sheet. Quite convenient smilies/smiley.gif
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written by K. Townsend, September 13, 2009
Hey ... I recognize that squegee in photo number 9! smilies/wink.gif Looks to me like you're laying a bit too much paste onto those fine-pitch QFN pads, though? Are you getting many bridges? If you don't have surgeons hands placing the chip and you smear a bit of the paste, I'd be afraid to make bridges simply because there's so much paste and it has nowhere to go, 'solder resist' or not. It's not the end of the world for QFP (you can fix it with an iron), but for QFP/DFN/etc., it's harder to fix or even see if there are any bridges. I've been trying to leave part of the pads empty simply because I get less bridges with bit of extra space. Covering about 60-75% of the pads I've been getting solid joints, and absolutely no bridges even on larger 0.5mm pitch devices. (Haven't had a bridge since I started laying down a bit less paste!) Just my own two cents worth, anyway, trying to get a decent reflow workflow going myself.

Enjoy the time in CA. I'd love to go to do some shopping myself (most of the companies I deal with seem the be in CA or Texas). smilies/smiley.gif

Kevin.
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written by Akiba, September 13, 2009
Yeah, you're correct. I'm getting bridges on my fine pitch parts so I clean them up with a soldering iron after the reflow. I'm still tweaking the size of the openings on the fine pitch parts and I think I need to reduce the length of the QFN and USB holes. That's why it's nice that I can cut stencils on my CNC. I don't really see any types of faults on the discretes like 0603 or 0805 components or the xtals, electrolytic caps, etc.
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written by K. Townsend, September 24, 2009
Those radio boards look sweet. Like the white ... well 'off-white' ... finish as well. I need to try a few colours and see what works for me. I added a few AT86RF230's to the basket at Digikey a while ago, but I'd rather just take advantage of all the work you put into getting the board working properly. (Hard work pays off later. Laziness pays off right away. :-) I'm assuming you plan on making a CC2520 board with the same standard connector as well? I'd have to look at whether the chip is easily available here in Europe (in 'normal' quantities), but it could be interesting if I find a useful source for them. I'd definately pick up a couple in any case.
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rp protypers
written by Ammara, April 13, 2014
Nice job.Informative blog.
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