Category Archives: Weather

Destroyed the barometer, oops.

So, it turns out, if you populate the MPL3115A2 upside-down, it shorts out the I2C bus and nothing works.

But I did manage to scrape it off the board.  Unfortunately, I damaged the PCB in the process and won’t be able to reinstall the barometer.  But I was able to salvage the rest of the board, so I can use this one as a dev test board until I get the firmware completely sorted out. 😀

Building the Mini Weather Station v2

Last night, I gathered all the parts for the Weather Station and did some assembly.  Installing a few dozen parts by hand, on a 12.5cm² PCB is an intricate process.

I start out with a huge printout of the PCB layout, an unpopulated PCB, and this excellent anti-static parts tray from iFixit.  All the big and identifiable parts go here.  When I’m feeling more energetic, I sometimes print out a specially-formatted parts list that goes under the tray, but I didn’t do that this time.  Just out of frame, there’s a stack of bags with hundreds of tiny surface-mount capacitors, resistors and inductors.  Since they’re not easily-identifiable, I keep them in labelled bags and deal with one at a time.

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Next, I align the solder paste stencil over the bare PCB and squeegee the paste onto the board.

Before:

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After:

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That paste is made out of microscopic balls of lead-free solder, held together with a sticky material called flux.  As you can see in the photo above, it’s not a perfect application of paste, but the reflow process is somewhat forgiving: the surface tension of molten solder helps to settle the parts into better alignment.

About a half-hour with curved ESD-safe tweezers, and the board is fully-populated.  At this point though, all the parts are simply resting atop the sticky paste.

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Into the oven!

This is a modified toaster oven, that I use for the sole purpose of baking electronics.  There’s my new board, ready to get baked!

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I really did have far too much fun building this toaster… I ripped out the existing thermostat and timer, and installed my own completely custom control panel and temperature control circuitry.  And it does a pretty decent job of following the time/temperature curve that I programmed into it!

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A few minutes later, and after it’s all cooled down, I’ve got a completed board!

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One commented-out line of code…

So it turns out, the original Mini Weather Station v1.1 board does still work, and it is still sending data to the Internet.  Well, it was trying to, anyway.  Turns out it was getting stuck because a line of JavaScript just wasn’t getting called.

Mini Weather Station v2

Last winter, I built a device that I called “Mini Weather Station.”  It is a small plastic enclosure which contains a thermometer, barometer and hygrometer.  And of course, a microcontroller, realtime clock and a 2.4GHz radio module.

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It worked reasonably well for a few months, even though it had a few minor design flaws.

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Yeah, that little piece of red wire is a sign of one of those minor design flaws.  The other problem isn’t as obvious from the photo.  I had originally intended the microcontroller to run at 1MHz on its internal oscillator.  But when I did, the barometer stopped playing nice with the microcontroller.  While I am able to run everything at 8MHz for a little while, the µc starts to become unreliable as the battery depletes.

Last time, I thought the battery was dead.  So I replaced it with a fresh one.  But, no matter how fresh the battery, it’s no longer transmitting.  The culprit seems to be some corrosion on a few of the radio module’s solder joints.

While I’m disappointed that the board has failed so soon, it’s given me an opportunity to address the design problems.

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Here, I have a new board design with space reserved for a 4MHz ceramic resonator, a new expanded debugging header, and a completely redesigned board layout to better suit the orientation of the finished PCB in the plastic enclosure.

This still won’t solve the corrosion problem, though.  I found something called a “conformal coating”: a nasty chemical which claims to protect against moisture, corrosion, fungus, thermal shock, and static discharges.  I haven’t bothered with it before, mostly because I didn’t know that it was even a thing.  But even though it’s starting to cost me far too much money, this whole fake engineering thing is about trying new things and learning, with eye protection and safety gloves, of course.

With any luck, this iteration will prove to be far more reliable than the last one!