Computing stuff tied to the physical world

Wrapping up

In AVR, Hardware, Musings, News, Software on Oct 6, 2013 at 00:01

I’m writing this post while one of the test JeeNode Micro’s here at JeeLabs is nearing its eighth month of operation on a single coin cell:

DSC_4507

It’s running the radioBlip2 sketch, sending out packets with an incrementing long integer packet count, roughly once every minute:

Screen Shot 2013-10-04 at 15.44.58

The battery voltage is also tracked, using a nice little trick which lets the ATtiny measure its own supply voltage. As you can see, the battery is getting weaker, dropping in voltage after each 25 mA transmission pulse, but still recovering very nicely before the next transmission:

Screen Shot 2013-10-04 at 15.45.45

Fascinating stuff. A bit like my energy levels, I think :)

But this post is not just about reporting ultra low-power consumption. It’s also my way of announcing that I’ve decided to wrap up this daily weblog and call it quits. There will be no new posts after this one. But this weblog will remain online, and so will the forum & shop.

I know from the many emails I’ve received over the years that many of you have been enjoying this weblog – some of you even from the very beginning, almost 5 years ago. Thank you. Unfortunately, I really need to find a new way to push myself forward.

This is post # 1400, with over 6000 comments to date. Your encouragement, thank-you’s, insightful comments, corrections and additions – I’m deeply grateful for each one of them. I hope that the passion which has always driven me to explore this computing stuff tied to the physical world technology and to write about these adventures, have helped you appreciate the creativity that comes with engineering and invention, and have maybe even tempted you to take steps to explore and learn beyond the things you already knew.

In fact, I sincerely hope that these pages will continue to encourage and inspire new visitors who stumble upon this weblog in the future. For those visitors, here’s a quick summary of the recent flashback posts, to help you find your way around on this weblog:

Please don’t ever stop exploring and pushing the boundaries of imagination and creativity – be it your own or that of others. There is infinite potential in each of us, and I’m certain that if we can tap even just a tiny fraction of it, the world will be a better place.

I’d like to think that I’ve played my part in this and wish you a lot of happy tinkering.

Take care,
Jean-Claude Wippler

PS. For a glimpse of of what I’m considering doing next, see this page. I can assure you that my interests and passions have not changed, and that I’ll remain as active as ever w.r.t. research and product development. The whole point of this change is to allow me to invest more focus and time, and to take the JeeLabs projects and products further, in fact.

PPS. Following the advice of some friends I highly respect, I’m making this last weblog post open-ended: it’ll be the last post for now. Maybe the new plans don’t work out as expected after all, or maybe I’ll want to reconsider after a while, knowing how much joy and energy this weblog has given me over the years. So let’s just call this a break, until further notice :)

Update Dec 2013 – Check out the forum at jeelabs.net for the latest news about JeeLabs.

Flashback – Anatomy of a transmission

In Hardware on Oct 5, 2013 at 00:01

One of the really fun things I always like to work on, is to push the envelope on power savings in the JeeNode.

It all started long ago, but over the years, I did refine the measurement process as my insight and instruments both got better. Here’s the most primitive approach, inserting a multimeter in series with the power supply to measure the static current consumption:

dsc_2597

The big problem with this is that a multimeter is far too slow to really see what’s going on. Only static idle current can be measured this way.

Another approach was to use a second JeeNode as power consumption tracker with some extra circuitry, to measure the voltage drop repeatedly:

Screen-shot-2009-12-19-at-16.27.09

This design can capture spikes by performing lots of repeated measurements, and in this particular case it even had a fairly large measurement range of 1 µA to 60 mA. This was done by using two separate sensing circuits and switching between them as needed.

But the real breakthrough came mid 2010, when Jörg Binkele sent me an oscilloscope snapshot of the voltage over a small series resistor. Here is one of the last ones, after lots of power saving techniques had already been applied:

detail_power_use1

As you can see from the annotations, there is an incredible amount of information one can glean from such oscilloscope traces.

This was one of the main reasons for me to learn more about oscilloscopes and eventually to buy a modern one myself – as described in a couple of posts, such as this one.

The capabilities of a modern digital storage oscilloscope (DSO) are truly phenomenal – and much of it is not even that much affected by the actual price range, although their cost does tend to keep them out of reach for occasional hobby use.

After many days of tinkering, it became possible to produce a very detailed map of the current consumption of a sensor acquisition + packet transmission cycle, as seen here:

annotated-room-packet1

The “haircomb” is the power consumption while sending individual bytes over SPI to the RFM12B module (and the received ACK after that), whereby the ATmega is even going to sleep between those bytes. For reference: the entire trace on this last screen is similar to the little blip marked “RFM12B transmission” on the previous screen. It’s not only considerably more detailed, but actually calibrated in 5-mA steps on the vertical axis.

Fascinating stuff, and no doubt a major reason why JeeNodes can perform so well nowadays in terms of ultra-low power consumption. If you had asked me this in 2008, I honestly would never have thought such a level of insight and performance to be attainable by anyone without access to a big research lab!

Flashback – Dive Into JeeNodes

In AVR, Hardware, Linux, Software on Oct 4, 2013 at 00:01

Dive Into JeeNodes (DIJN) is a twelve-part series, describing how to turn one or more remote JeeNodes, a central JeeLink, and a Raspberry Pi into a complete home monitoring setup. Well, ok, not quite: only a first remote setup is described with an LDR as light sensor, but all the steps to make the pieces work together are described.

More visually, DIJN describes how to get from here:

dijn01-essence.png   dijn01-diagram

.. to here:

Screen-Shot-2013-02-09-at-12.22.13

This covers a huge range of technologies, from embedded Arduino stuff on an ATmega-based JeeNode, to setting up Node.js and the HouseMon software on a Raspberry Pi embedded Linux board. The total cost of a complete but minimal setup should be around €100. Less than an Xbox and far, far more educational and entertaining, if you ask me!

It’s all about two things really: 1) describing the whole range of technologies and getting things working, and 2) setting up a context which you can explore, learn, and hack on tinker with in numerous ways.

If you’re an experienced Linux developer but want to learn about embedded hardware, wireless sensors, physical computing and such, then this offers a way to hook up all sorts of things on the JeeNode / Arduino side of things.

If you’re familiar with hardware development or have some experience with the Arduino world, then this same setup lets you get familiar with setting up a self-contained low-power Linux server and try out the command line, and many shell commands and programming languages available on Linux.

If you’ve set up a home automation system for yourself in the past, with PHP as web server and MySQL as back end, then this same setup will give you an opportunity to try out rich client-side internet application development based on AngularJS and Node.js – or perhaps simply hook things together so you can take advantage of both approaches.

With the Dive Into JeeNode series, I wanted to single out a specific range of technologies as an example of what can be accomplished today with open source hardware and software, while still covering a huge range of the technology spectrum – from C/C++ running on a chip to fairly advanced client / server programming using JavaScript, HTML, and CSS (or actually: dialects of these, called CoffeeScript, Jade, and Stylus, respectively).

Note that this is all meant to be altered and ripped apart – it’s only a starting point!