Computing stuff tied to the physical world

Archive for October 2013

Wrapping up

In AVR, Hardware, News, Software, Musings 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:


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 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:


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:


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:


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:


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, Software, Linux 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:


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!

Flashback – Easy Electrons

In Hardware on Oct 3, 2013 at 00:01

The Easy Electrons series is a set of weblog posts which were published end of 2010 and beginning 2011 to try and bring across a bit of intuition w.r.t. electronics.

Many many times, people not trained in electronics struggle with the concepts of voltage vs. current, wonder why some component suddenly overheats, what a capacitor does, why you need a resistor in a certain circuit, or how large that resistor should be.

Unlike software, hardware and electronics are bound by the laws of physics. Painfully so, in fact – you can damage stuff when hooking things up incorrectly, and you can even get hurt if the voltages or currents involved are high enough. And it’s not just AC mains that can hurt you: even a car battery can be dangerous if you don’t know what you’re doing.

Knowing why things happen is extremely important in electronics. And learning the basics is really just a matter of reading up on it and investing a bit of effort. There’s no magic – in fact, there is so much knowledge about electronics nowadays, that you really can predict and explain stuff, even before hooking things up.

Since I loved tinkering with electronics as a teenager, I was lucky to gain a good deal of very intuitive knowledge about electronics early on. So much so, that basic DC electricity knowledge became second nature to me. Ohm’s law is not some technical rule, it’s obvious – the linear relation between voltage and current, and the fact that resistance is simply the slope of that relationship, is so ingrained by now, that I don’t even think of Ohm’s law as something distinct from the essence of electricity. Same for Kirchhoff’s laws – and the water analogy which works so well in so many cases to match intuition to the real world.

So the Easy Electrons series was born – no math, no theory, just a set of posts which tackle a number of electronics concepts in what I hope can bring across some of that intuition. My drawing tools at the time were based on paper and a scanner, so the drawings were a bit crude and hard to read – here’s an example where I’m trying to explain how to drive LED strips which draw more power than the weak I/O pins of an ATmega can provide:


There are posts about voltage and current, about power and heat, about resistors and capacitors, about LEDS and diodes, and about transistors and MOSFETs, to name a few.

Don’t take my word for it, heck… don’t even read my posts if you don’t want to – all I can say is: if you ever hook up electronics circuits of your own imagination and invention: get to grips with the basics, so you’ll understand why hooking up a bunch of LEDs in parallel is usually not such a good idea, why using a power supply with a higher voltage is likely to lead to overheating and damage, and why hooking up relays and motors often requires extra protective circuitry.

It’s not hard, it’s not magic, it requires no math of any sophistication (and there’s always the brilliant Khan Academy if you want to brush up on it anyway). It can be exhilarating to be able to design and predict what a circuit will do before hooking anything together.

Electronics is a truly wonderful field to explore (and it’s huge!). You don’t need much to experiment with, and you will learn a lot – if only to become quite respectful of the laws of physics, which are merciless (still: most mishaps are harmless and nothing gets damaged).

You’ll run into everything from “nothing happens” to “it’s smoking”, and it’s terrific fun!

Flashback – Ports and I2C in JeeLib

In AVR, Software on Oct 2, 2013 at 00:01

One of the small innovations in the JeeNode is the use of “Ports”:


Most µC boards, including the Arduino, brought out all the I/O pins on one or more large headers, meaning that you had to pick and route individual pins for each case where some component or sensor was being connected. While flexible, it prevented adding stuff in a plug-an-play manner: hook up some sensors, use matching bits of C/C++ code, and done.

I also always kept running out of VCC and GND connection pins while experimenting. So instead of bundling all I/O pins, a decision was made in 2009 to bring out a couple of (nearly) identical “ports”, to any of which the same sensor could be attached. That meant you could connect up to at least four sensors independent of each other.

As it turns out, there are enough spare I/O pins on an ATmega to provide one digital and one analog pin to each port. Add GND, VCC (+3.3V) and PWR (the input voltage, could be up to about 13V), and you end up with a fairly general-purpose setup. One extra spare pin was provided as “IRQ” to allow connected sensors to draw attention to themselves via an interrupt, although this feature has admittedly so far not been used much on JeeNodes.

But the real improvement is the fact that the two I/O pins can be used as I2C bus. All of a sudden, each port is no longer limited to a single sensor. The I2C bus is so useful because many types of low-cost chips include an I2C interface in hardware, and it lets multiple chips operate on a single bus.

One of the first extensions added was the Expander Plug, an 8-bit general-purpose digital I/O interface. So now, with just two pins consumed on the ATmega, you could have up to 32 input/output pins (by daisy chaining 4 of these plugs and setting them each to a different I2C address). The Dimmer Plug takes this even further: up to 8 of them on one bus, each driving up to 16 LED’s – for a total of 128 dimmable LEDs on 2 I/O pins!

Officially, the I2C bus requires dedicated hardware with “slew control” to increase the accuracy of signals on the bus. And while the ATmega has such an interface, there is just one per ATmega. Fortunately, you can also “bit-bang” I2C in plain software, i.e. simulate the relatively slow pin changes with nothing but software on any 2 I/O pins. The speed is not quite as high, and the supported bus length is also limited to a few dozen centimeters, but for direct connection of a few plugs that still works out quite well.

And so the JeeNode has ended up having 4 “ports”, each of them individually capable of supporting either I2C, or one analog (AIO) and one digital (DIO) pin – or alternately 2 digital I/O’s, since each analog pin on the ATmega can also be used in digital mode.

Since then, lots of different types of “JeePlugs” have been created, some I2C, some not. Most of the plugs have a corresponding class and a demo sketch in the JeeLib library, making it very easy to hook them up and interface to them in software. With most plugs, you just have to define which port they are connected to – and in the case of I2C plugs, which bus address they have been set to.

The placement of these ports and the choice of very low-cost standard 6-pin headers took some experimentation, but I think it all turned out ok. Lots of expandability and flexibility.

Flashback – The first JeeNode PCB

In AVR, Hardware on Oct 1, 2013 at 00:01

The first JeeNode circuit board was very exciting to make, back in January 2009:


Initially, I just wanted to get the connections right and didn’t care for silkscreen labelling, so there was none. It was created with CadSoft’s EAGLE, a commercial package with a freeware version for small boards. The “JeeNode” name came a month later, by the way.

The learning curve of the EAGLE package is steep, but then again, drawing this sort of stuff is going to be complicated whatever you do, because it’s not about drawing a nice picture where only aesthetics matter, but a meticulously designed diagram of which all the paths and connections have to follow certain rules, such as wires not crossing (doh!) and wires all having a minimum width and separation.

Here’s the JeeNode v6 PCB in comparison, of which many thousands have been produced:


It’s still surprisingly similar in design to the first iteration, although the production details and fabrication process have greatly improved over the years. One aesthetic detail I’ve always been pleased with is the blue-with-gold color choice. The gold plating is easier to solder than the HASL process I used initially, and is much more resistant to corrosion. Don’t think too much of this gold layer, by the way: it’s chemically deposited (fairly nasty stuff, from what I understand) and only a few atoms thick. Still… enough to do its work, and visually attractive (all in the eye of the beholder, evidently).

The purpose of a PCB is three-fold: a physically strong base for all the components, a reliable interconnect between all the pins to implement the actual circuit design, and silkscreen labelling to ease assembly and use afterwards.

The result: a tangible product. Quite an exciting change for a software developer used to work with bits and bytes, and who could never before point to the “real” result of it all!