I’m Baaaaaaaaaaaack!

March 22nd, 2013

After a bit of a hiatus (due to my new router ignoring all attempts to persuade it to forward port 80), I have finally brought the blog back up again — by installing the server running it elsewhere.

Shop Demo Software Shenanigans

June 9th, 2012

Back in the 1980s, a friend of mine had some serious phun with BBC model B’s in stores that also sold software.

He would take a box of 5.25 inch floppy disks, all but a few of which was labelled “Watford Electronics Compatibility checker”. (Watford Electronics were a third-party supplier of peripherals; they made an improved disk system for the BBC, better than but slightly incompatible with the “official” Acorn upgrade and some software, especially games, would not work with it.)

So my friend would ask to “check” if a game would be “compatible” with his Watford disk system. Inserting the “compatibility checker” disk into the drive of a BBC computer and pressing shift+BREAK produced a fancy screen with a progress indicator; which then asked for the game disk to be inserted, thrashed the drive a bit, then asked for the checker disk again. After a series of such disk swaps came the dreaded announcement that the game was not compatible with the WE DFS. He would return the compatibility checking disk to the back of the box, and ask the shop assistant if he could compatibility-check another game. While the assistant was away fetching it, my friend whipped out the compatibility-checking disk from the front of the box (nobody ever noticed this blatant switch, which was done with no sleight-of-hand) and booted it up.

Again the compatibility-checking process would require several disk swaps, and again it would fail. And my friend would wander off, dejected, before the shop assistant could work out what had just happened right under their nose.

What had happened, of course, was that the “compatibility checker” disk contained a program that loaded itself into RAM, then copied the game disk sector-by-sector first to RAM, then to the “checker” disk (overwriting the original copy of itself into the bargain, but it was already running from RAM, and each of several disks in the box contained a copy of the same software.) As there was only 32KB of RAM and some of that was eaten up by the OS, copying a 100KB disk (yes, you read that right: 102 400 bytes) had to be done in stages.

Radio may soon be Nobody’s Bomb (bumped)

November 16th, 2011

Beside the promise of extra channels (meaning more adverts), there is a dark and sinister side to the switch to digital radio and TV broadcasting.

Analogue radio, and even analogue colour TV, were much closer to Universal Comprehensibility than their digital equivalents.

Building a MW / LW radio receiver is not hard — years ago, nearly every schoolboy did it. Building one that works well under all circumstances is tricky, but amplitude modulation — which is used on the medium and long wave bands — is basically easy. You have a high-frequency carrier signal, which you make get weaker and stronger in time with the audio signal getting weaker and stronger. You feed this into an aerial system, and invisible electromagnetic waves travel away from it in all directions. The person listening has a tuned circuit, which lets through just the frequency of your carrier signal; a rectifier, which converts the high-frequency alternating current into direct current (which is still rising and falling in time with the audio signal); and an amplifier, which boosts the signal enough to move a loudspeaker cone. That’s a bit of an oversimplification, but I don’t want to lose my audience.

Frequency modulation is a little bit harder. This time, instead of varying the strength of the carrier signal, you vary the frequency Where your oscilloscope trace is above the zero line, you move the peaks closer together; where it goes below the line, further apart. So the frequency of your carrier signal is changing. This isn’t as big a problem as it sounds, because most tuned circuits aren’t perfect; so the one in the receiver will let through frequencies that are within a certain tolerance anyway. You also need a different kind of detector, which responds to changes in frequency as opposed to amplitude; but once you have built that, you can make use of the same power supply, amplifier and loudspeaker as before.

Doing it with pictures involves another layer of complication since there is no single, universally-accepted way of representing a picture as an electrical signal. And that’s just in mono — don’t get me started on the various ways people have actually transmitted colour pictures. In practice, though, agreements were thrashed out between governments, broadcasters and setmakers on a country-by-country basis, so all the TV sets in any given country worked on the same broadcast standard. And home video equipment works to national broadcast standards precisely so that an ordinary television set can be used to view home recordings.

Still, the fact remains that anyone with the right knowledge can build a radio transmitter. (Actually using it is another matter; if your signal travels far enough to interfere with other users, you can expect to end up in court. Not much is likely to happen if you build a small, low power transmitter and nobody finds out about it. And if the Rule of Law has already broken down …..)

But digital broadcasting is a whole other kettle of fish. Even building a digital receiver requires access to proprietary technologies (and this includes mathematical operations over which some people claim to hold patents!), although they may be available under what appear to be generous licencing terms. This is only because the big corporations are aware that in order to sell transmitters, receivers need to be almost given away. Building a transmitter is what requires access to the seriously expensive stuff, and that’s what they aren’t going to let Our Sort near.

Call it paranoia on my part if you like, but there’s no denying that wholesale adoption of digital broadcasting will end up making it nigh-on impossible to start an underground radio station — and in so doing, will deprive The Population At Large of a potentially extremely useful weapon against a corrupt government.

I was a squatter once …..

November 2nd, 2011

….. for two nights, at any rate.
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Thoughts on “Singular They”

September 12th, 2011

English lacks pronouns for the third person singular common gender. The plural forms are commonly used as singular for want of anything better, but this seems to be frowned on by The Authorities. And although there have been various suggestions for sets of common-gender pronouns, none of them have really caught on — despite there being entire science-fiction anthologies without a “he” or “she” in sight.

I personally think we should stop acting as though there is anything wrong with using “they” in the singular. After all, outside certain dialects, English no longer makes any distinction between singular and plural in the second person, and the distinction is often blurred in the first person (traditionally, the reigning monarch has always referred to themself as “We”; and this is also often used as a literary device to indicate that the author is not alone in expressing a particular opinion. There are also instances when multiple authors have referred to themselves as “I”.)

So, for the sake of consistency and to avoid introducing new words into the language, I propose that the “overloading” of common-gender third person plural pronouns as singular pronouns be made official.

  • Nominative: They
  • Accusative: Them
  • Genitive: Their
  • Reflexive: Themself (only obvious singular form)

We already use such constructions informally all the time. So why not just make them formal?

Why your car insurance is going up

March 11th, 2011

Basically, it’s because people are making false claims. Even down to the point of staging deliberate accidents (and it’s surely a matter of time before an innocent third party gets involved in such an incident).

I have two suggestions which ought to help. Firstly, require, as part of the MOT test, for head restraints — the purpose of which is to prevent whiplash injury — to be fitted and properly deployed. Then, any claim for compensation for whiplash injury will require admitting to driving an unroadworthy vehicle.

And secondly, motor insurance fraud should attract an automatic driving ban.

What’s really needed, though, is for more personal injury lawsuits to be dismissed with prejudice. We don’t need any new laws for this; we just need to enforce the ones we have. Once a few people have been labelled as “vexatious litigants”, the rest will soon learn.

Spammers can get lost

October 25th, 2010

A lot of comment spam has been coming from IP addresses in the following netblocks:

173.234.0.0/16
173.208.0.0/16
69.116.0.0/16

Fortunately, I know how to use IPtables :)

# iptables -A INPUT -s 173.234.0.0/16 -p tcp -m tcp -j DROP
# iptables -A INPUT -s 173.208.0.0/16 -p tcp -m tcp -j DROP
# iptables -A INPUT -s 69.116.0.0/16 -p tcp -m tcp -j DROP

Blocking a /16 is a bit of a Nuclear Option, but I’m sick of it. No doubt this is going to block a few legitimate users too ….. my recommendation is to switch ISPs, because you are doing yourself no favours associating with an ISP who are friendly to spammers.

(If I get any comment spam in response to this post, I will approve it — after blocking their IP addresses — but with links disabled.)

Fun with media files

September 4th, 2010

It has to be said, mplayer is an amazing piece of software.

It can play ISO files as though they were DVDs. First, mount the image;
$ sudo mount -oloop /path/to/dvd_image.iso /media/dvd
Then to play the first programme from the disc;
$ mplayer -dvd-device /media/dvd dvd://1/

Now, the discs created on my standalone DVD+R/RW recorder are a bit weird, in that the .vob files on the disc don’t correspond with the recorded programmes. So I can’t save an individual programme just by copying its .vob file; meaning, if I wanted to keep a whole series together, I would have to record all the episodes on the same disc.

But mplayer has an option, -dumpstream which simply extracts the MPEG data from the source and saves it to a file. The default filename is stream.dump but you can specify an alternative filename with -dumpfile /path/to/somewhere. And without having to display anything, it isn’t constrained by the frame rate. Don’t be alarmed by the “Core dumped ;) ” message — that’s just hacker humour.

So we can extract the second programme from a disc (or a mounted ISO image), and save it as an MPEG file, with a command like the following;
$ mplayer -dumpstream -dumpfile /path/to/saved_file.mpg -dvd-device /media/dvd dvd://2/
Remember, this is the actual MPEG data from the disc, so it’s already a DVD-like MPEG2 file; and therefore suitable for burning to disc with your favourite DVD authoring application. Or just saving onto one of those USB external hard drives with a built-in media player.

Don’t forget also the excellent ffmpeg, which can convert nearly any media file format to nearly any other media file format.

Making Sense of your Gas Bill

January 30th, 2010

This is how to interpret a British Gas gas bill.

Your gas meter measures cubic metres of gas flowing through it. (The old ones used to measure cubic feet; but the gas companies switched to proper measurements longer ago than the lifetime of a gas meter, so they should all be cubic metres by now.) But your bill is calculated on the number of kilowatt-hours of energy liberated from the gas.

On your bill, there will be a calculation such as this:

metric units used 239 * calorific value 39.3572 * volume correction 1.0226400 / convert to kWh 3.6 = gas used in kWh 2448.43

So what do the figures mean?

  • metric units used is the number of cubic metres of gas measured by your meter.
  • calorific value is the number of megajoules of energy in a cubic metre of gas, at some specified combination of temperature and pressure.
  • volume correction is a “fiddle factor” to account for seasonal variations in air pressure and temperature. When it’s cold, the molecules are more densely packed, so you get more energy in the same space. When the atmospheric pressure is low, the gas molecules are free to jiggle about more, so you get less energy in the same space. Each molecule contains a certain amount of potential energy stored in the bonds between atoms. So the calorific value depends on pressure and temperature, which is why this calculation is required.
  • conversion to kWh is because there are 3.6 megajoules in a kilowatt-hour. (A watt is one joule per second; there are 3600 seconds in an hour. Kilo means * 1 000 and mega means * 1 000 000.)

Given these figures, you can work out how many kWh are in one cubic metre of gas, simply by doing the same calculation for 1 metric unit used. According to the above, it is 11.23 kWh per m; but this figure may well be different for you, as the volume correction is seasonally-dependent.

But that’s not the whole story. The price per kWh depends on how many units you have used, with the first few kWh each day being more expensive. There will be a section like this:

2448.43 kWh used over 103 days
First 756.00 kWh @ 6.846p = £51.76
Next 1692.43 kWh @ 3.275p = £55.43
Total cost of gas used = £107.19

The higher rate applies to 756.00 kWh over 103 days, and adds an extra cost of 3.571p per kWh. As long as we actually use up all the “expensive” kWh, we will end up paying a fixed extra amount each week. If we are allowed 756.00 kWh in 103 days, then that is equivalent to 756.00 * 7 / 103 = 51.38 kWh in 7 days; which will cost us an extra 51.38 * 3.571p = £1.83 on top of what they would have cost if we had only been paying 3.275p for them.

Meanwhile, one cubic metre of gas on the meter gives us 11.23 kWh and so costs us 36.78p. So, our weekly bill will be equal to £1.83 plus 37p for each m of gas used.

Simples! :)

If you ask your gas supplier nicely they will send you a payment card, which can be used at local shops to make payments towards your gas bill. All you need to do is to work out the cost of the gas you have used each week (basing it on the figures from your last bill, which probably won’t be the same as mine), and round it up or down to the nearest whole pound.

The Embargo is Lifted

September 15th, 2009

Now that the person who was not to know about it is safely home, I can finally reveal the home improvement I recently had carried out:

Esse 100 SE

Esse 100 SE


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