Building Widgets – My SMD Build Process

Well, back from a short break away (kid free woohoo!) and onto some widget builds. I thought I’d document how I do my widget construction. I actually find building SMD devices much easier than the PTH variety.

I have all my components in some neat snap together containers, this allows me to have everything at hand for the build.
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Widget running on the smell of a single AA

For the next version of the widget, I’m planning to have an on board boost regulator. This design will allows the widget to run from just about any voltage source as low as 0.7v (so NiMh will be fine) and up to 5.5v, this boost regulator in conjunction with a standard LDO regulator will give me a nice input voltage range of 0.7v – 12V. Before I finalise the design I wanted to test things to see how well it’ll work.
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Simple Low Pass Noise Filter

The other day while playing around with the ADC on the widget I had some problems with noise causing the reading to bounce around, It needed some form filtering to remove the noise. Normally almost everyone seems to take a number of readings and then average the result, unfortunately this takes time.
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Widget Sensor Housings

I want to deploy widgets around the home, both inside and out, so I needed to find something that would allow some protection from the environment to the electronics, cheaply and easily.

On the weekend while doing some shopping I found the solution in the kitchen area of the local discount store, at $1.50 a piece it was the right fit for the job. They probably won’t like U/V in the long run, but will see how they go, at that price I can replace cheaply.
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Reading Widget Battery Voltage

In my previous blog entry I described adding a solar cell to the widget and how I could measure the voltage produced by the Solar Cell, however I still need to monitor actual battery voltage easily, and preferably with not a lot of additional hardware.
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Solar Powered Widget

 Solar Powered Widget board

One of the tasks I want to use the widget boards for is a Wireless Sensor Network around the house for measuring environmental values. The sensors that I want to live outdoors will need to be self sufficient in terms of power, so I wanted to see if I could charge the batteries via solar, of course this can be done, but again I want to do it as cheaply and as simply as possible, I also want the widget board to monitor the solar voltage and report it back.

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Build Documentation

Strobit RFM12B PCB Layout

I’ve started to document the Wireless Widget Board in the wiki, documentation is currently all over the place, but slowly getting there.  Currently I’m working on the build instructions so those of you that I’ve sent PCBS to can at least have a parts list.  

I’ve also put up an initial bill of materials. But it would be great if someone can do a Octopart BOM and share it.

Initial building instructions can be found here: http://code.google.com/p/strobit/wiki/Rfm12BuildingInstructions with more to come.

Strobit Wireless Widget Photos

I had a chance to grab a few photos of the progress so far, also helps that most of my components that I had on order arrived today so the boards has been kitted out with all the headers. Now I can plug the prototype personality in, still waiting on my crystals, switches, and diodes.
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Preliminary RF Tests

Today I did some testing on the RF side of things,  nothing scientific, just walking around the house seeing if it would dropout or report bad checksums, I’m happy to reports all is working as expected (using the 915Mhz RFM12B module)

The tests are done by using the RFM12B Example sketch found in the JeeLab RFM12B library by Jean-Claude over at Jeelab (RFM12B Arduino Library)

This library runs unmodified on the wireless widget board, just follow the instructions in the README about setting up node ids.

From the preliminary testing using some compact 1/2 wave GSM 900MHZ/1800MHZ antennas (http://www.dealextreme.com/details.dx/sku.5237)  I’m easily getting all the way around the house with no dropouts, have yet to do outside tests.