Freesteel Blog » The Sky of Things

The Sky of Things

Monday, May 11th, 2015 at 11:44 am Written by:

I picked up on the Chicago Array of Things by this clip at the BBC.

Here’s a screen grab of the circuit as the guy is showing off his hardware kit.

click1

I was struck by the similarity with the kit I’ve been working with and taking on my (frustratingly infrequent) hang-gliding flights.
palvario1

It shouldn’t be a surprise that they look the same. All we’ve done is bought all the cheap mini sensors we can buy and soldered them together onto one board.

The Chicago group make a big thing about the beauty of their hardware box design, which it is. But what do you DOOOO with the data? This is the question I posed to the Barcelona SmartCitizen Sensor Kit whom I saw at the MakerFaire in Newcastle a couple of weeks ago.

The answer was the usual: we put the data on the internet so that anyone can download and do whatever they want with it.

Like WHAT?

And so on.

I have to harangue because I am on constantly on the lookout for techniques and people who are where I’m at with this type of sensor data. There are no adequate tools. I am constantly hacking different trials and plots of the data using bare Python and discovering all sorts of things that are important.

For example, I don’t think these sensors are quite right. The digital compass needs calibration every time you plug it in, and the accelerometer was biased in one of its planes.

And here is the graph of the humidity in RED, windspeed is the horizontal green squiggly line, and barometric pressure is the white line.
humidbarow
The humidity only got to 90%, having started at 70%, which means I only got 2/3rds of the way to cloudbase. Note how as the barometric readings go down (with altitude), humidity is going up, because the air temperature (not displayed) is getting colder and approaching the dewpoint.

The humidity value is waving about all over the place, and then it settles down as soon as I take off (at the vertical yellow line). Then it begins waving around everywhere before I come in to land 50minutes later (the vertical lines are at 5minute intervals).

I don’t know the reason for this. Is it the windspeed? Is it the proximity to the ground?

My experiments on a bicycle have been inconclusive, not least because the vibration of the road tends to shake many of the components loose. And I can’t peddle fast enough.

You can tell immediately that there’s a lot more to getting something useful from these devices than simply taking the digital readings and assuming it’s the truth.

We had this problem in cave surveying when digital compasses and clinos came about, and people made totally buggered up mistakes and wildly out of calibration cockups that they never would have done with a mechanical instrument. Just because it’s an electronic number you tend to want to write it down to two decimal places in degrees. But if you were using the analog compass you might have actually noticed the way it swings when you hold your helmet light or steel karabiner too close enough to it to affect the magnetic field.

We like these digital devices because we don’t need to think. Just put the uncalibrated values on the internet and hope that someone else can do the thinking for you.

I will only know that these sensor folks are on the same page as me when they get desperate and one day nail every single sensor node they own onto the same lamp-post in order to see to what extent they agree at all. And then I’d like to see the existence of some software that is actually able to correlate the measurements between the different devices to account for their variability.

That’s my demand. It’s what I call “Test Driven Development”, except the Tests are lavished on actual real things that matter which you don’t know about (such as the repeatability of these measurements), not on pointlessly obvious-when-they-fail bits of self-contained code. That’s the kind of TDD I won’t truck with when I am lost in a sea of uncertainty as to what is to be done. For months I am having to do the equivalent of programming doodling and sketching of ideas. Not possible to produce any finished artwork design.

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