Computing stuff tied to the physical world

Cheap power analysis

In Hardware on Apr 21, 2013 at 00:01

Remember this screen shot?


It was a carefully captured analysis of the power consumption of a JeeNode, running the RoomNode sketch, and sending / receiving wireless RFM12B packets. There’s a fantastic amount of info in there, to help understand which part of the code and which activity is drawing the most power. It was a great help at the time to reduce power consumption, allowing these nodes to run well over a year on a couple of AA batteries.

Trouble with this, is that you need an expensive piece of equipment, called an oscilloscope. Long-time readers might remember that I’ve written extensively about this. These things cost anywhere from a few hundred Euro, to thousands, or even tens of thousands for high-end units. I ended up settling for a Hameg HMO2024, which is a great instrument, but with a pretty hefty price of well over €1000.

So how would you go about analysing the power consumption of your sketch without plunking down this sort of cash? Well, there really are not that many alternatives, you have to see the current-vs-time graph to be able to understand what’s going on.

Luckily, there is a fairly capable little unit from Gabotronics, called the Xminilab. It pushes an ATXmega (note the “X”) to its limits, allowing it to capture quite a bit of information, just like its bigger brothers. It even includes things like FFT analysis, an 8-channel Logic Analyser, and an AWG Signal Generator! Last but not least, the software is open source.

Interested in how capable this $69 device is? Well, check this out:


Do you recognise the waveform? The Xminilab has captured a packet transmission, a bit like the one shown at the start of this post (it’s a different sketch, i.e. radioBlip2, hence a different pattern). It may not look like much, but it should be sufficient to see the effect of changes in the code and to optimise power consumption with it.

So, do you need a scope? IMO, anyone wishing to explore electronics should have one. Whether second-hand or the above-mentioned Xminilab, it really helps to be able to see things in a way where our human senses fall short – such as these brief events. It’s the most versatile instrument in the lab, if you ask me – even with a 128×64 pixel LCD screen.

PS. I don’t recommend the even lower-cost $49 Xprotolab (which I also have). It has the same functionality, but with its tiny OLED display it really is too hard to read, IMO.

  1. JC

    We’ve discussed these units last year, indeed? As from my communication with vendor:

    “The features and specifications are the same on both products, with the exception of the board and display size.

    The Xprotolab measures 1”x1.6” and has a 0.96” display. The Xminilab measures 3.3”x1.75 and has a 2.42” display.”

    I’d like to try the lower unit (Xprotolab) still in USB mode, because it could be combined with any Android tablet with OTG. So a portable battery powered scope …

    Would you borrow your Xprotolab to me? Especially if you do not play with it any more ;)

    PS: It is pity but none of advanced (Xminilab and Xminilab-B) models is available for order now.

  2. In the photo of the Xminilab connected to the JeeNode, I see the wires change colors, indicating something is occuring off screen. Could you comment on how you connected the two devices?

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