Nothing Untoward - STATIC ARCHIVE

WARNING: This blog post is one long incoherent rant. Read at your own risk.

Recently my Samsung Galaxy Nexus developed a fault: It wasn't detected when plugged in via USB and it wouldn't charge (except very slowly when switched off). I read that this was a common problem and the USB port needed to be replaced. Since it was under warranty, rather than spending a fiver and half an hour of my time, I thought I'd exercise my consumer rights by sending it in to Samsung for repair. Bad move, as it turns out.

I phoned up the call centre and soon it was booked in to A-Novo for repair. I posted off my phone in the jiffy bag they provided and the next day, my phone was marked as "Non defect (working properly)" on the website. A few days later I got an invoice for GB£138 to replace a cracked screen. Needless to say, there was nothing wrong with the screen when I sent it in. I had the option of paying this charge, paying an unspecified administrative charge for the phone's safe return without repair, or letting them destroy my phone.

I phoned up A-Novo who said that since the packaging wasn't damaged there was nothing they could do, and that I should contact Samsung instead. I decided this was a job for another day. Then the next day, they returned my phone without any warning. I put the battery in, switched it on and found that there was still no damage to the screen. By Hanlon's razor, I'll attribute this to crass stupidity rather than intentional deceit. Anyway, I phoned up customer service again. The person on the phone apologised and, after putting me on hold to talk to her manager, booked my phone in to another service center (Regenersis).

After I sent my phone into regenersis, they returned it fixed within two days, yay! Unfortunately, they also unlocked the bootloader (which tends to void one's warranty) and reflashed it with the wrong software - I sent it in with android 4.2.2 and they sent it back with 4.1.1. At this point I decided to cut my losses and reflash it myself rather than sending it back in. So I now have a working phone again, but not without a huge amount of stress and hassle.

I used the "Email the CEO" feature on Samsung's website to complain about my experience, but all I got back was an email from (presumably) some customer service rep containing the usual "we're sorry to hear this" platitudes. Overall, I wasted a lot of time dealing with Samsung over this. Would not recommend.

A couple of weeks back I stumbled across a thing on ebay. The seller described it as an "Aircraft stable oscillator" but knew nothing more about it. I was interested for two reasons: firstly, it was made by GEC Marconi - a predecessor to the company I now work for. And secondly, from the name it sounded like it might contain an OCXO - which would have been handy to use as a frequency reference. Anyway, it was £20 delivered so I figured I may as well go ahead. Here it is:

Let's crack it open! Not much to see yet. The main board has some 74HC series logic, a 7805 linear regulator, a P-channel mosfet and a couple of 2n2222 NPN transistors on it. On the far right you can see a power supply decoupling board - not sure exactly what the filter topology's called but it looks like two cascaded pi filters. You can also see marks on the inside of the case which show that it's been machined.

From another angle you can see a thermostatic switch underneath the board.

Removing the PCB and thermostat and taking out the mounting posts, I could then extract this:

An atomic clock for £20! Excellent! I had a look at the datasheet to find the pinout. Tracing the tracks on the original circuit, it seems that this variant was a single-supply one, needing only +15V (EDIT: actually 19.5-38v, see addendum). Most of the circuit seemed to be dedicated to just switching the green lamp on once the frequency had stabilised (these units take a few minutes to warm up) and the red lamp on otherwise - so nothing particuarly interesting here.

Some variants of these could have their frequency set by RS232 but this particular model didn't seem to be one. I hooked it up to a bench power supply and measured the output - an 800kHz square wave.

This was slightly annoying - I was hoping for a 10MHz reference for my test equipment. I wondered how I could change the frequency. Perhaps I could multiply the output frequency by 25 somehow and divide by 2? Maybe by filtering out the 5th harmonic of the square wave twice, or using a PLL? The datasheet hints that these devices can be set to a frequency of your choice out of the factory, so perhaps i could change the frequency of mine in the same way that they set them initially? I opened it up and found that all of the interesting circuits inside were potted with what seemed like some sort of polyurethane foam.

Just as I was running out of ideas - being too afraid of damaging it to try removing the foam - a friend recommended that i try the time-nuts mailing list. I asked on there if anyone knew how to change the frequency of these and was met with a number of very helpful responses! Unfortunately most of the information they had was on the FE-5650A-58 option with the RS232 control but i did extract a number of useful bits of information here. Firstly, all of these devices have a 50.255MHz clock at their core (the big metal can in the picture above!) and mine most likely uses a DDS chip to create the output from that. Also, changing the output frequency isn't quite as easy as just changing the DDS tuning word since they tend to use crystals on the output for filtering.

As an interesting piece of background, i also found out from G8RPI that these oscillators are from a frequency hopping system called HAVE QUICK.

Anyway, with this information i was sufficiently intrigued to risk picking away at the foam to find out what was going on. With the majority of the foam removed I could see the DDS chip - an AD9955. I'm not very patient when it comes to reading things but the gist i got from skimming the datasheet was that a signal goes into CLK, a 32-bit word F is input in parallel and the output frequency is Fin*F/2^32. On this board the 32 DIP switches are clearly to set F, Another thing I noticed was that the DDS isn't actually set to 800kHz - at the top left is a 4040B ripple counter, which divided a 12.8MHz clock down by 16 to produce the output.

I wanted to verify my theory that the AD9955 was dividing down the 50.255MHz clock down to 12.8MHz. Reading the DIP switches (assuming that in to the board=1 and towards the edge=0), the tuning word was set to x4134111F. Dividing this by 2^32 and dividng 12.8MHz by this gives 50.255058MHz... pretty much spot on! From now on I'll take this as the frequency of the reference clock.

So, i now know how to change the DDS divider, but what about the crystal filter? I figured this must be underneath the board I was looking at, so I undid the nuts holding it in place and gently pryed it off. (Be careful of the header and loose wires connecting the boards near the SMA connector end!) Underneath, sure enough, was a crystal. It seemed to be connected (possibly via a resistor?) to the COUT pin of the DDS. The markings (156/Y-1294-2) didn't seem to indicate its frequency or manufacturer and googling them didn't help. Regardless, I desoldered it to unlock the frequency range of the DDS chip.

By some simple maths i calculated the tuning word for 20MHz was x65E15AC0. Why 20MHz? Well, i was going to have to put a crystal back in eventually, but i couldn't find any 10MHz ones in my junk box! I had plenty of 20MHz ones though so i decided to improvise... i'd make a 20MHz clock, then rewire the 4040B counter to divide by 2 rather than 16. This also has the advantage of giving me a CMOS logic buffered output. Anyway, i switched it on and probed it to find my 20MHz signal i was after. It was a bit ugly because of the lack of filtering though.

Here you can see i've bodged in a replacement 20MHz crystal. I've wrapped it in kapton tape and grounded the end, just like the original one. This one was a smaller package though, so I had to scratch away some of the soldermask from the PCB to tie the can to ground.

I fired it up again for a smoke test. As hoped, i saw a 1.25MHz square wave on the output - the by-16 divider still in place. Next job was to change the divider to by-2. This simply involved disconnecting the output from Q4 of the ripple counter and connecting it to Q1 instead. In doing so, I noticed that the output was decoupled with a 330pF and 100pF capacitor across the SMA connector. At 10MHz, this amount of capacitance won't do, so i... ripped the capacitors off with a pair of pliers.

With this done, i put it back together and revelled in my success! The error in frequency here is almost certainly due to the innacuracy of the counter (bought for a tenner at a radio rally) rather than of the source.

Thanks to Herbert Poetzl, Robert G8RPI Atkinson and Bill WB6BNQ - all from time-nuts - for their invaluable advice with these frequency standards! After I found one of these inside the Mysterious Aircraft Part, i decided to buy the seller's remaining stock (another 6 of them) since a rubidium frequency standard must be worth more than £20. I'm now selling them on ebay and I'm considering offering them with 10MHz modifications. Once I've extracted the frequency standards, I'm left with a very nice machined aluminium casing which will make a great project box - it's aluminium with fins so will be good for high power dissipation stuff. Audio amplifier project maybe? The cases also seem to be IP67, with the power switch and connectors rated thus and a rubber gasket around the edge where the two sections come together. Perhaps it's time for an underwater electronics project!

ADDENDUM 1: Input Voltages

Since i wrote this post, Robert G8RPI has pointed out that these units aren't actually designed for a 15v input voltage! They actually have a switching pre-regulator on board, as you can see below. This buck regulator is set with a 91kohm resistor to give a nominal output voltage of 15.3v. I measure it to actually be nearer 15.5v. With a dropout voltage of 4V, this gives a permissible input voltage range of 19.5-38v. This is apparently so it could be used directly from an aircraft's 28v supply. I could have easily removed this board by undoing the screw, prising off the edge which is potted to the Rb package, desoldering it from the main power supply board and placing a short between where the ECW and the yellow wire used to go. I decided to keep it for now though - it will be quite handy to be able to run this thing from an old laptop charger!

ADDENDUM 2

So, some people have gotten a bit upset that I bought all of these and am selling them on for more. I appreciate it's frustrating but... hear me out. For £20 I bought a completely undocumented part on a hunch - for all I knew it could have been completely worthless. I took on that risk of losing out. Once I'd found that it was actually worth something, I spent hours of my time dissecting and documenting it here. So I'm now selling on a documented part - you know what's inside it and you don't have that risk of losing out! Also, I have college bills to pay :) Tl;dr: I charge a premium for the elimination of risk and for my time.

I've listed a complete unit on ebay since it seems like some people would be interested in getting hold of the whole thing.

A while back I heard some samples of the difference between lossless files and their compressed forms (MP3) and thought it seemed pretty cool to hear what data the compression algorithms are throwing away. I just got around to trying this for myself. Here's what I did:

• First things first, you'll need sox with the appropriate formats installed. Optionally install octave, and vorbis-tools or a compressor of your choice. On debian: apt-get install octave sox libsox-fmt-all vorbis-tools
• Start with a lossless file, eg a FLAC or a WAV ripped from a CD.

$ sox ~/Music/Dalriada/Jegbonto/05\ -\ Téli\ ének.flac original.wav

• Convert it to a lossy format. I'd reccomend using vorbis, since I had trouble with MP3, see below. For example:

$ oggenc -q 5 -o lossy.ogg original.wav

• Convert the compressed file and original to RAW format. Check that they're the same size.

$ sox original.wav original.raw
$ sox lossy.ogg lossy.raw
$ ls -l *raw

• Start octave or matlab and run the following commands to subtract the files as 16-bit signed ints (alternative follows):

> original=fread(fopen('original.raw'),Inf,'int16');
> lossy=fread(fopen('lossy.raw'),Inf,'int16');
> fwrite(fopen('out.raw','w'),original-lossy,'int16');

• Alternatively, if you don't have/want to install octave, Techmeology provides some C code to acheive the same thing.

$ gcc -o compare compare.c
$ ./compare original.raw lossy.raw > out.raw

• Now convert it to a usable format (eg wav). Optionally you can amplify it to bring it to an audible volume level. Here I've applied 10dB of gain:

$ sox -r 44100 -t raw -e signed-integer -c 2 -b 16 out.raw out.wav gain +10

And there you have it. I was left with a sort of haunting ghostly screaming sound. I would share but you know, copyright and all that. If anyone can suggest some creative commons music to publish samples of though, I'd be happy to do that.

I have noticed a problem though - by converting to MP3 and back you seem to end up with fewer samples. I've tried padding it out with zeros before the comparison, but it then the difference file becomes just a choppier-sounding version of the original. If anyone knows how to resolve this, please do let me know.

Today I made red onion chutney. My method, summarised concisely:

Slice N red onions and cook on the hob at a low heat with a little oil. I used a lid but I'm not sure if this was nescassary. For me it took about 20-30 minutes before they were soft.

Add 37.5N millilitres of red wine vinegar and 25N grams of sugar. Leave to boil on a low heat. I left the lid on for about 10 minutes then took it off and turned the heat up, letting it reduce.

Once it was of a chutney* sort of consistency, I considered it done and put it in a jar (cleaned out and sterilised with boiling water), then let it cool. For N=4, I made enough to fill a 450g curry sauce jar.

The finished result, served with cheddar and crackers: Omnomnom

Edit: I should add, in hindsight I would have cut the onions a bit thinner - it came out a bit coarse.

*I hereby claim "chutney" as an adjective. Chutney, chutnier, chutniest.

In thermodynamics, we consider two related but substantially different properties of a system: energy and entropy. Both are hard to define - we might say that energy is "the ability to do work", but this isn't really true - consider a hot lump of metal. It certainly has energy, but the second law says we can't extract work from it without a colder reservoir. And even then we need to consider Carnot to tell us how much of this we can actually access. This definition applies better to exergy - the amount of energy available to do work, but let's not complicate things for now. When it comes to entropy though, we struggle even more to find a satisfactory description. Some would describe it as a measure of disorder, some tell us we don't need to define it in words - if we deal with it enough, we'll become comfortable with what it means.

But I find entropy troubling. Depressing, even.

Energy is a nice concept. Energy is always conserved - no matter what you do with it, it will always be there, just converted between its various forms. Entropy, on the other hand, via the second law, essentially states that in the fullness of time everything turns to shit. In everything we do, we make our energy less useful, everything a bit more samey and our toast a lot more burnt.

Entropy says you'll never get back out what you put in.

Entropy says you're on a one way street to a frozen demise.

Entropy says that one day everything you own will count for nothing.

Entropy says your first true love will never take you back.

Entropy says "things have changed, we have to move on".

Entropy says that you'll eventually die cold, unhappy and alone.

Entropy says there's no light at the end of the tunnel, because it's all fucked off into heat.

Entropy is the mistress of the universe - and a cruel mistress she is.

(This rant was adapted from a recent facebook status)

I went into the kitchen this evening to find this: Free greengages! I have no idea what a greengage is, but I remember it's something you make jam with. So I looked up a recipe, and found that Jamie Oliver recommends 1 part sugar to 2 parts greengages (by mass). And some other crap too, but we can forego that. I didn't have any scales, but luckily I did have a steel rod lying around... I marked out a position about 2/3 of the way along, put a rubber band around it to hang it from, then tried as best i could to balance the greengages on the short arm with the sugar on the long arm. I cut the greengages and plums in half and left them to simmer in the sugar.

The recipe suggested that the stones should float to the top. They didn't and I had to separate them out manually with a wooden spoon (if I'd known, I'd have taken them out beforehand...)

Either way though, the final result was delicious! I just had some on toast... omnomnomnomnom

Just a quick one for this morning... My experiences with an in-car inverter, along with a bit of a rant. (edit: having finished writing this it's turned out not to be quite as short as I expected. Sorry!)

I bought one of these broken off ebay a while back for 99p - I figured I'd replace the output transistors on the H-bridge and everything would be fine. It arrived and I opened it up - what I saw was utterly horrific. The inverter circuitry was just a 556 circuit and was about 15Hz (30%!) out of callibration. The DC-DC converter is completely open loop: at 15V input (within spec!) it will put out around 400V. There is an optoisolator but it doesn't seem to do anything most of the time, although shorting the output switched the thing off so I think it has something to do with the thermal cutout. The inverter circuitry has a few more ICs alongside the 556 timer which I'm guessing provide some sort of crude RMS voltage regulation by varying the pulse width but quite frankly I can't be fucked to try and work it out because clearly someone couldnt be fucked to design this thing properly and I'm just plain fed up of it by this point. On top of this, the mechanical design was shoddy - the PCB was held in place by the transistors. I cannot stress strongly enough - do not buy one of these. I'm not sure if these design flaws are common to all in-car inverters but they're certainly widespread. If you do need an in-car inverter, I don't know what to suggest. Build your own, I suppose... sorry. Or if you must buy a cheap one, be aware of their limitations.

Anyway, here's what I did with mine: after I was unsucessful in fixing the problem by replacing the H-bridge transistors, I couldn't be bothered to do any more faultfinding and decided to demote it from inverter to DC-DC converter. It would quite happily put out ~300VDC, so I figured this would be fine for anything with a switch mode power supply. I removed the H-bridge transistors and soldered the live and neutral lines to the +ve and -ve rails. Here you can see the top of the PCB where i've removed the transistors and the underside of the board where I've soldered the cables to the rails:

(in the second image, you can also see where I cauterised my finger by touching the 300V rail)

I plugged my laptop charger in and hoped for the best, being ready to catch the magic smoke if need be. All went well and I'm now writing this with my laptop charging from this inverter. It won't be good for much else since DC is no good for line frequency transformers or voltage doubler circuits, but I'm happy that I have something I can use my laptop with in the car. Yeah, a bit of a cop out option - I could probably have fixed it if I could be bothered but I deemed it not to be worth the effort. It works with my laptop charger anyway so that's all that's I care about.

I scrawled a warning on the top just in case this deathtrap finds itself in someone else's hands. I derped a bit writing the date:

Ohai, first post and all that. Whatever.

I've been looking into building a reprap lately, mostly just because it would be awesum to have one on my desk, but also because there have been plenty of situations when i've thought, "I wish i had a reprap right now..." I decided on the Prusa mendel iteration 1, because i was told that there are a few problems to be ironed out with iteration 2.

The printed parts were loaned to me by Glen Searle, who runs a 3d printing business. I would tell you to check out his website but it seems to be down at the moment. How do you loan parts though? Surely i need to build them into my own printer? Well the answer is I build mine, print out a new set of parts and give them back to him. I also bought an extruder hot end off him for £50 - he threw in some threaded rod too. (edit: Glen has asked me to add that the non-sky-blue parts were printed while we sat there eating pizza. And good pizza it was too.)

I've also ordered a couple of other non-printed parts: I got some stepper motors and linear bearings from aliexpress (essentially like ebay but cheaper and more chinese) and I'm basically going to get the rest of the mechanical parts from screwfix/ebay. I'll post links for my complete bill of materials when I'm done, but for now I don't want to be making recommendations before I'm sure I haven't been ripped off myself.

Today I was at the hackspace working on the heatbed for my reprap. I have a load of 160x100mm photo etch PCBs, so i figured I could do something with that - cut them down to squares and tesselate four together to make my 200x200mm heater bed. I'm not yet sure how i'll fix them together but we'll cross that bridge when we get there... Anyway, I decided on a zig-zag patten of parallel tracks, 2mm apart and d wide. I did some calculations to find d based on the fact that a typical heater bed resistance is 2 ohms (so I aimed for 0.5 ohm per board) and the copper will be 35 microns thick. As you can see from my calculations below, I ended up with a track width of 2.28mm. If enough people hassle me for it, I might write a script to automatically do these calculations and spit out an SVG file. Although this time round I was lazy and made the design in libreoffice. PDF is here.

I etched these boards at the hackspace today using cheap (not FR4) board, and here's the result:

First impressions were these seemed to have been a success. I measured the resistance of one with a multimeter and it came out as 0.5 ohms. I then hooked them up to a few linear power supplies and found that they didnt actually get that hot: with 9 amps flowing through them, they were still less than 100 degrees. At 7 amps, they seemed to be about an ohm each. Not to worry though, nothing which can't be solved by MOAR VOLTZ: I'll just wire them up differently: either 12V straight across one or 20v in series parallel. That's all for now, I'll document all further progress here. But first I'll leave you with a picture of my test setup: for those times when two linear PSUs stacked on top of each other just don't cut it...