Tag Archives: mpl3115a2

Office Robot Modules

I originally wanted to design and build all the parts for this robot on a single PCB.  I figured that would look nicer.  But I’m really glad that I’ve opted for a modular approach to the whole thing.  It’s made it so that I can focus on one problem at a time, and it makes it easy to replace and/or reuse components.

Here’s a diagram of all the modules that will eventually be part of the robot.  Colour indicates what’s been done so far, and what remains.

OfficeBot Architecture

Blue

I’ve completed building the Motion Controller and Dual Motor Controller boards.  They’ll need some firmware changes to support additional boards, but aside from a minor hardware issue on the Motion Controller (which I’ve been able to work around by using other hardware for the testing, these are looking pretty decent!

Pink

Prototyped, or in-progress.  I’ve built a website that’s currently being served up by the robot itself.  That’ll be moved to a terrestrial web server, eventually.  The connections between the Pi and the rest of the hardware is now breadboarded.  Although it looks hideous with all those jumper wires, it does work nicely.  But I need to sort out an issue with the power supply before I can have the PCB manufactured, so it might just be a little while for that.  I can live with the ugly wires (for a little while).

Orange

What was I thinking?!

I designed the Motion Controller board with support for analog distance measurement sensors and collision switches, as well as lighting control for illumination and hazard lights.  What robot would be complete without a whole whack of blinkenlights?

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. 😀

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.

IMG_3827.JPG

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

IMG_3828.JPG

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.

EAGLE screen shot

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!