Nathan Hurst's home page

Contact me at .

8 July 2014, 3:41 UTCSolar panels are getting cheaper

Six years ago I wrote that Solar panels aren't getting much cheaper, today mental told me that Solar has won. I realised when I read this that I missed an important effect, namely, that there is a massive positive feedback as you move towards the balance distance capturing most of the market. This is because not only is there more people with shorter distances, but in addition, as people move off grid, the price of the grid for the remainder increases.

Perhaps in the near future the utilities will being paying people not just for excess capacity, but also paying them for the connection. This would be to provide for the large centralised users such as aluminium smelters and skyscraper offices who will still require more energy than they can produce locally. See also the disappearance of the telephone landline.


5 June 2014, 16:17 UTCFlowers of xenon

To answer a question at work about plasma physics I bought the cheapest plasma sphere I could find. We didn't get a conclusive answer on the original question, but playing with it brought up some interesting behaviour:

I asked Jan if he could explain this and he's done some digging:

jan: The globe is prepared by pumping out as much air as is practical. The globe is then back-filled with neon to a pressure similar to one atmosphere. If the radio-frequency power is turned on, if the globe is "struck" or "lit", now, the whole globe will glow a diffuse red. If a little argon is added, the filaments will form. If a very little xenon is added, the "flowers" will bloom at the ends of the filaments. says wikipedia

njh: ok, so the answer is xenon. But I was more interested in why. (And why does xenon make this happen and not neon?)

jan: sure, just a piece of evidence - the fact that it's caused by addition of another noble gas should tell something, but I am not sure what.

jan: my roommate says

jan: it could be similar mechanism, the symmetry breaking

jan: so I talked to a guy who does plasma physics (tokamaks), he had an interesting observation

jan: the electrical field in the shape of the 'petal' is there even without the xenon, it's just xenon glows in right region, so the petal shows up

jan: the fact that the petal is very red supports this:




jan: if I was optimistic I would say that xenon has the lowest energy bands

I'll need to dig out my spectroscope and see if I can determine the precise wavelength.


22 April 2014, 1:47 UTCEntry
Consistency is the hobgoblin of distributed systems.


18 March 2014, 4:43 UTCHead to tail in 1 line
We were talking about puzzles on friday, and the old 'head' to 'tail' puzzle came up. I commented off the cuff that I thought it could be done in 5 lines, Jay took this as a challenge. When he told me that, I felt obliged to find such a solution.


9 March 2014, 2:20 UTCWhat do penny sizes in nails actually mean?

(coauthor Jay)

In Australia nails are measured in mm for diameter and length, a common house nail is 100m long and 4.2mm in diameter. In the US, nails are measured in pennies. Wikipedia has quite a bit to say on this topic:

Penny sizes originally referred to the price for a hundred nails in England in the 15th century: the larger the nail, the higher the cost per hundred. The system remained in use in England into the 20th century, but is obsolete there today. The d is an abbreviation for denarius, a Roman coin similar to a penny; this was the abbreviation for a penny in the UK before decimalisation.

But this seems a little implausible, given that in the 15th century, wire nails were not actually available. In the talk section there is an alternative theory

In Folk-etymology: a dictionary of verbal corruptions or words perverted in form or meaning, by false derivation or mistaken analogy, published by G. Bell & Sons, 1882, Abram Smythe Palmer says, "Ten-penny nails are not nails ten of which may be got for a penny, but properly ten-pun'y or ten-pun'-nails, i.e., ten-pound, large nails, a thousand of which will weigh ten pounds (the old form of the verb to pound was pun). "It is surprising how slowly the commonest mechanical terms find their way into dictionaries professedly complete. I may mention, as instances of this, that penny, a denomination of the sizes of nails, as a six-penny or a ten-penny nail, though it was employed by Fently two hundred years ago, and has been in constant use ever since, is not to be found in Webster. — Marsh, The Eng. Language, p. 126 (ed. Smith). "Six-penny, eight-penny, ten-penny nails, are nails of such sizes, that a thousand will weigh six, eight, or ten pounds, and in this phrase, therefore, penny seems to be a corruption of pound." ...and he then goes on to quote a couple of usages from earlier literature (Abel Redivivus and Jokes and Wit of Douglas Jerrold). So, can anybody verify the origin of the term tenpenny nail as currently given in our article? rowley (talk) 20:08, 1 February 2012 (UTC)

This seems somewhat more plausible. Our methodology is to weigh 10 12D, 16D, 20D and 30D nails randomly selected from a paper bag of nails from the local hardware store. So let's see what the numbers look like:

the least squares line is y = (1.27*x/penny - 8.6) gram with 6.2 residual. So not a strong correlation, but still vaguely plausible. Perhaps the fact that these are hot dipped gal nails upsets things slightly? Anyway, so we take 1000m and it should weigh exactly 1 pound:

You have: 1.27*1000g
You want: lb
	* 2.7998707

Well, close. I guess.


24 November 2013, 7:36 UTCSeattle sunset

Sometimes you can take really nice pictures from a moving car.


23 September 2013, 1:28 UTCSingularities and gimbal lock

I wonder if The Singularity can't happen until Ray Kurzweil dies?


11 July 2013, 5:08 UTCA simple English to American translator


7 February 2013, 5:34 UTCGetting Ubuntu 12.10 on an Acer Aspire S7 191-6640

update (2014): Others have had luck in using the most current (13.10) ubuntu installer directly, so you should try that out before going this more complex and error prone route.

After many false starts and pain I found a way to boot linux on my aspire which doesn't miss any of the functionality. I have not got things coexisting with windows 8, but I can live with that. I happened to have a usb stick with ubuntu 12.10 installed sitting on my desk. Start it in try before you buy mode. The first step is to back up your windows partitions. I did this using a back hard disk mounted at /media/ubuntu/1234etc with dd if=/dev/sda of=/media/ubuntu/1234etc/laptopwindows8sda, dd if=/dev/sdb of=/media/ubuntu/1234etc/laptopwindows8sdb. I got an amazing 150MB/s write to a spindle disk using this! I have restored from this without trouble.

I am booting using the legacy boot mode. After spending a long time trying to get uefi booting to work before I discovered the problem was the raid controller, but I am loath to switch back to uefi. People have warned me that others have had really bad experiences with uefi with current builds, so I'm going to leave that one until others have walked the path. So legacy boot system. I could not get the bootloader to be found with the raid turned on, so I've switched to software raid, which is a little heavier weight power/cpu wise. But it works (touch wood).

So I've made both ssds have the following:

To turn on the software raid:

mdadm --create --verbose /dev/md0 -n2 --level=0 /dev/sda1 /dev/sdb2

I initially put --level=1 here but someone contacted me to confirm. It should have been level 0 (128GB total, no redundancy).

Put a file system (I couldn't get the installer to create a file system directly on md0):

mkfs.ext4 /dev/md0

Then use the built in installer with the 'other' option to select the md0 mounted as /, /dev/sda1 as biosboot (although I don't think this is actually needed), /dev/sdb1 as /boot. It automagically found the swap partitions.

After this the system would boot the kernel, but not mount /. To fix this I came back into the installer (try without install) and remounted target (and /target/boot /target/dev /target/dev/pts /target/sys /target/proc /target/run) and chrooted in. It also helps to cp /etc/resolv.conf /target/etc/resolv.conf so that you have internet in the target chroot. Then I updated and upgraded the apt. Then make sure you install mdadm in the target. This will rebuild the initrdfs so that it has the appropriate module for mounting /dev/md0. Finally, I recommend if you have the space just dd if=/dev/sda of=/backup/laptopsda and similarly for /dev/sdb so that you can quickly restore.

I imagine this would work on all the related models. (S7 391-6810 and S7 391-9886)

On Fri, Feb 28, 2014, Stefan wrote:

I read your description of getting Linux onto the Acer Aspire S7; I tried various options, using the fakeRaid and software raid as I didn't want to go the lazy root (sic :) of just splitting the device in two and not making use of the full potential the laptop has. I came actually to the conclusion that your solution seems to be the only one at the moment that can make use of the raid system :) ... so thanks again for pointing me into the right direction!!

I use Kubuntu 13.10, and so far everything (including touch screen and almost all FN keys) seems to work out of the box.

P.S: I also measured the raid with dd, I managed to get 330 mb/s write speed, so that is quite satisfactory!

Best wishes



27 December 2012, 2:40 UTCCapacitive sensors with the Teensy 3.0

The Teensy 3 is not only an Arduino, it's an ARM too. And a neat built-in feature is the capacitance sensor available on 12 of io pins. I've always been a fan of capacitance for measuring things, so having a stable, fast and efficient way to do this with no external components is amazing.

This will probably make my water level sensor obsolete, if it has as low drift.

So let's see what we can do with it. The first step is to just see if we can get values out:

void setup() { Serial.begin(38400); } void loop() { Serial.println(touchRead(A9)); delay(100); }

Looking at the serial console I can see lots of 700s, which corresponds to 14pF, which is respectable given the protoboard.

Second step: make a simple slider:

The copper triangles are cut from a piece of flashing, the whole thing is hot-glued to a piece of PET packaging I had lying around.

The aluminium bar is connected to ground to see if I can improve the noise levels. It didn't help. What I probably would need to do is form multiple 'fingers' with alternating grounds. But that's not something I'm going to try and cut out of a piece of flashing.

The code is very similar, but this time we want to look at the relative capacitance between two pins:

void setup() { Serial.begin(38400); } void loop() { int a = touchRead(A9); int b = touchRead(A8); Serial.println((a-b)*1000/(a+b)); delay(100); }

Sliding my finger from one end to the other gives me:

-91, -89, -100, -109, -110, -107, -118, -123, -115, -109, -101, -96, -92, -80, -75, -60, -50, -38, -25, -15, -9, 8, 9, 22, 20, 37, 32, 42, 41, 52, 45, 48, 50, 49, 66, 71, 77, 84, 91, 99, 105, 111, 112, 123, 128, 127, 133, 132, 130, 127, 123, 125, 121, 112

Unfortunately I'm seeing a lot of noise when I don't earth myself.

To detect finger presence we could just threshold the total capacitance:

if (a+b > 2000) Serial.println((a-b)*1000/(a+b));

Though this requires coming up with a number (e.g. 2000 = 40pF) once you have assembled your system. There is a probably a clever way to do this by looking at the long term averages.


24 December 2012, 6:58 UTCSimple way to make a position measuring hinge
16 October 2012, 5:52 UTCSpectra from my super cheap spectrometer
16 June 2012, 4:44 UTCCheese platters are a very clever piece of ancient technology
1 January 2012, 2:20 UTCaeolus organ synth moved to github
26 November 2011, 12:07 UTChacking the KIS-3R33S power supply to drive 10W LEDs
20 August 2011, 10:55 UTC3d rocks
27 July 2011, 9:58 UTCSweetApartment 3D
23 July 2011, 4:18 UTCTesting my new stealth clothes
29 June 2011, 10:58 UTCImplementing the Hogwarts great hall ceiling.
23 May 2011, 12:22 UTCCome as you aren't party
23 May 2011, 10:16 UTCBarrington Tops partir deux
22 May 2011, 12:18 UTCFrank L Baum the Chiroptologist
1 May 2011, 12:22 UTCBarrington Tops
24 February 2011, 0:30 UTCMoss garden
18 December 2010, 9:11 UTCDowntime
15 December 2010, 9:10 UTCThe cat twist
21 October 2010, 10:43 UTCIn Brugge
9 September 2010, 3:43 UTCPlant identified
4 September 2010, 9:21 UTCBlogger turns 11
30 August 2010, 14:00 UTCA trip to Royal National Park

All older entries

[atom feed]