EEVblog #856 - Mailbag

[EEVblog]

More Mailbag Monday



SPOILERS:
Qiktag Indiegogo
https://www.indiegogo.com/projects/qiktag-it#/
Apple iMac Power Supply
Victorinox Minichamp Swiss Army Knife
Caran d'Ache pen
Kübrich Ingenieure Hose Clamp aren't the Dodgy Brothers
http://www.kuebrich.com/
HF Splitter Teardown from Bitshift Dynamics
http://www.bitshift-dynamics.de/
The finiest Audiophoolery from Nordost, the Odin reference speaker cable:
http://nordost.com/odin-supreme-reference/odin/speaker-cable.php
And a package for Sagan

[indole]

Looks like the SD audio board is similar to http://www.ebay.ca/itm/TF-card-U-disk-MP3-Format-decoder-board-module-amplifier-decoding-audio-Player-M-/291687925029

Cheapo MP3 player, maybe hack one together into a personalized FAIL button?

[muffenme]

The other one look like http://www.ebay.ca/itm/GPD2846A-TF-Card-MP3-Decoder-Board-2W-Amplifier-Module-for-Arduino-/381374686711?hash=item58cbb3e5f7:g:ttsAAOSwyQtVr3J3.   It's a GPD2846A TF Card MP3 Decoder Board 2W Amplifier Module.  Nothing to wright home about but for someone new to electronics then this could be cool.  This unit is a $2 USD item.
This bigger mp3 is a http://www.ebay.ca/itm/Audio-Player-Amplifier-MP3-Format-Decoder-module-3-7-5-5V-for-Arduino-/201467969361?hash=item2ee86d3f51:g:LMAAAOSwIwhWSYn9.  It's a Audio Player Amplifier MP3 Format Decoder module 3.7-5.5V. This unit a $3 item.

Great show.

[tpw_rules]

One interesting detail with the iMac power supply is actually how it fits in the computer's architecture. As opposed to a standard computer where the power supply takes mains in and outputs 5V, 3.3V, 12V, etc, that board only outputs 12V at 30 amps if I can read it right. There is another board with several DC-DC converters to generate all the system voltages, kind of like a laptop. This means a) if that board works, it's a fairly nasty 12V supply and b) you can run an iMac off a car battery. I had an older one with a failed mains board which ran fine like that. I'm not sure anything (except perhaps the hard drive) gets the input voltage so it was fine with any voltage from like 10 to 14 volts.

[Andy Watson]

Potter verb work, act in feeble, unsystematic way.

In the Old Dart, sheds are good places to potter.

[rrinker]

 So Down Under do you need to hook those fancy speaker cables up the opposite way so the nanobullshit particles don't all fall out?
 

[Don Hills]

That "orange peeler" thingy on the Minichamp is also useful for opening welded clamshell plastic bubble packs.

[SNGLinks]

Portion Down is a British government research establishment known for its controversial chemical and biological weapon research. https://en.m.wikipedia.org/wiki/Porton_Down

[Towger]

I though Daddy would have a laugh, even if most of it currently goes over Sagan's head. Many of the 'stories' are very British, even Yanks may not understand them.

From the days when engineers wore suits:

[LazyJack]

The pronunciation of Caran d'Ache is something like Caran-d-ash. It actually comes from the Russian word for pencil. See: https://en.wikipedia.org/wiki/Caran_d%27Ache_%28company%29

[rrinker]

 Those organized tins of hardware that Dave bought? That guy was clearly related to Roland.

[Fungus]

Am I the only one who imagined a mini Jacob's Ladder when I saw this?



All it needs is the right sort of transient... 


But come on: That thing has a backlight, a trimmer, a MOV, a proper shunt (trimmed with solder blobs) ... it's a luxury multimeter!

[kunzem]

on the cabletv amplifier the things are transformers for impedance matching and allow to injection the supply voltage into the signals.

[Groucho2005]

So Down Under do you need to hook those fancy speaker cables up the opposite way so the nanobullshit particles don't all fall out?
 

The cables do have to be hooked up the opposite way in Aussieland but the reason is another - The nanobullshit particles are constantly spinning within the wires but, just like water in a drain, they spin the other way in the southern hemisphere.

Also, these cables need a very long burn-in time until the molecules (and the nanobullshit particles of course) have aligned themselves for maximum listening pleasure. Before serious listening, burn them in with the amplifier at maximum power 24/7 for about 8 months.

[Zbig]

The cables do have to be hooked up the opposite way in Aussieland but the reason is another - The nanobullshit particles are constantly spinning within the wires but, just like water in a drain, they spin the other way in the southern hemisphere.

Also, these cables need a very long burn-in time until the molecules (and the nanobullshit particles of course) have aligned themselves for maximum listening pleasure. Before serious listening, burn them in with the amplifier at maximum power 24/7 for about 8 months.

I know that just trying to apply any reason to the "directional speaker cable" BS is a mistake but is this bunch really so dense that none of them actually realizes that audio signal is f*%^!$g bipolar? Like, the current flowing in each direction more or less half the time?

[Fungus]

this bunch really so dense that none of them actually realizes that audio signal is f*%^!$g bipolar? Like, the current flowing in each direction more or less half the time?

But... one end of the cable is connected to ground, isn't it?

[Groucho2005]

this bunch really so dense that none of them actually realizes that audio signal is f*%^!$g bipolar? Like, the current flowing in each direction more or less half the time?

But... one end of the cable is connected to ground, isn't it?

Not necessarily.

[Brumby]

eg .... a bridged amplifier.

[Groucho2005]

eg .... a bridged amplifier.

Or simply a symmetrical amp.

[rrinker]

So Down Under do you need to hook those fancy speaker cables up the opposite way so the nanobullshit particles don't all fall out?
 

The cables do have to be hooked up the opposite way in Aussieland but the reason is another - The nanobullshit particles are constantly spinning within the wires but, just like water in a drain, they spin the other way in the southern hemisphere.

Also, these cables need a very long burn-in time until the molecules (and the nanobullshit particles of course) have aligned themselves for maximum listening pleasure. Before serious listening, burn them in with the amplifier at maximum power 24/7 for about 8 months.

 Yes, I realized my mistake after posting. Clearly it is rotationally influenced, not up/down.  Hmm, perhaps someone needs to sell a burn-in rig so people can optimize their cable performance. Think your $100K cable gives you the best listening experience? Think again. Your cable can be even better after it is properly burned in to align 100% of the nanobullshit particles. Make sure you optimize your ultimate cables with our new BullBurner cable optimizer.

 Of course then the company making the cables would simply change over their literature to indicate that the cables are 100% burned in at the factory and come ready to use.

 Was that here, or somewhere else, that I saw the multi-thousand dollar 1 meter long Ethernet cable which was also 'directional'? Designed to optimize your MP3 experience.... 

[Zbig]

Even in the implementations it actually is, what's the difference anyway? Isn't these guys' point that the current flows "better" in the "right" direction of the cable? What does the presence or the lack of the ground reference on either of the amp posts change in that respect?

EDIT:
What I mean is: regardless of the implementation, your speaker's diaphragm doesn't sit half-extended during the silent periods of the audio signal, right?

[Brumby]

 Was that here, or somewhere else, that I saw the multi-thousand dollar 1 meter long Ethernet cable which was also 'directional'? Designed to optimize your MP3 experience.... 

I think you might mean this.  It was here....

https://www.eevblog.com/forum/chat/eevblog-2015-top-5-bullshit-products-award/msg822776/#msg822776

Audiophoolery unidirectional ethernet cable: http://www.audioquest.com/ethernet/diamond

USD$1195.00 for 1.5 metres of Cat 7 cable!?! Holy shit. Although not a bad business model; Invent some hocus-pocus that sounds kind of believable and morons will be throwing money at you.

I was going to think of something clever to go with a few excerpts from the site - but when I read this, the enthusiasm vanished...

DIRECTIONALITY: All audio cables are directional. The correct direction is determined by listening to every batch of metal conductors used in every AudioQuest audio cable. Arrows are clearly marked on the connectors to ensure superior sound quality. For best results have the arrow pointing in the direction of the flow of music. For example, NAS to Router, Router to Network Player.

   How the hell do they come up with this stuff?

[Groucho2005]

What does the presence or the lack of the ground reference on either of the amp posts change in that respect?

Nothing. 

[Groucho2005]

Also, these cables need a very long burn-in time until the molecules (and the nanobullshit particles of course) have aligned themselves for maximum listening pleasure. Before serious listening, burn them in with the amplifier at maximum power 24/7 for about 8 months.

I forgot to mention that the burn-in procedure cannot be done with just any signal or music material. For people who prefer a more relaxed and valve-like sound, use a mixture of Kenny G, Bananarama and Cole Porter. Make sure that the room temperature is between 22 and 24 degrees Celsius at all times.
For people who like a more analytical sounding system, use Sex Pistols, Kraftwerk and 50 Cent. Room temperature in this scenario should be between 18 and 20 degrees Celsius.

[FrankBuss]

What's wrong with these cheap Chinese multimeters? Of course, you shouldn't use it for measuring mains, the inside doesn't look very CAT II safe as printed on the top, and the cables don't have enough copper for 10 A, but otherwise it might be useful for reasonable accurate low voltage and resistor testing. Might even have a faster continuity tester than more expensive multimeters.

[Zbig]

What's wrong with these cheap Chinese multimeters? Of course, you shouldn't use it for measuring mains, the inside doesn't look very CAT II safe as printed on the top, and the cables don't have enough copper for 10 A, but otherwise it might be useful for reasonable accurate low voltage and resistor testing. Might even have a faster continuity tester than more expensive multimeters.

It just seems fashionable here, somehow

[rrinker]

What's wrong with these cheap Chinese multimeters? Of course, you shouldn't use it for measuring mains, the inside doesn't look very CAT II safe as printed on the top, and the cables don't have enough copper for 10 A, but otherwise it might be useful for reasonable accurate low voltage and resistor testing. Might even have a faster continuity tester than more expensive multimeters.

 I use them on my model railroad, it's all low voltage and some basic continuity checking for the most part. They're fine for that sort of thing, and when it gets dropped, or stepped on, or covered in plaster and glue, I just toss it and pick up another, often free. I would not want to subject my Fluke 8060, or a nice new 87V, to such abuse.
 When I need to make 'real' measurements, I use a 'real' meter.

[Macbeth]

I though Daddy would have a laugh, even if most of it currently goes over Sagan's head. Many of the 'stories' are very British, even Yanks may not understand them.

I laughed my arse off when Dave mentioned "Porton Down" as a shed. Clearly this is a troll book, indeed part of a comedy series for adults who were brought up on Ladybird books as children.

e.g. My favourite Ladybird book as a child Making a Transistor Radio. I wouldn't recommend an old TRF PNP design in nowadays it has to be said!

I think the subtleties of humour in the Old Dart go over Aussies heads maybe as much as it does the Americans?

The great thing with this book is it will still appeal to children despite the obvious to adults utter non Political Correctness. 

[Fungus]

For non-UK readers:

"Pottering" is what men do in sheds. It's nothing in particular, just pottering, doing your thing.

"Porton Down is where government workers will potter in the in the event of a Nuclear Attack."
 

[Macbeth]

Providing they aren't too busy experimenting with nerve gas on the enlisted ranks https://www.theguardian.com/science/2004/may/06/science.research

[thoper]

tell me the truth Dave, did you put your finger in that hose clamp and applied pressure?

[all_repair]

I use them on my model railroad, it's all low voltage and some basic continuity checking for the most part. They're fine for that sort of thing, and when it gets dropped, or stepped on, or covered in plaster and glue, I just toss it and pick up another, often free. I would not want to subject my Fluke 8060, or a nice new 87V, to such abuse.
 When I need to make 'real' measurements, I use a 'real' meter.

So it is not just me 
I get more value from cheap handtool than my expensive ones.  I am not afraid to abuse and to wear them out, and have kept sharpening them.  But the expensive ones like the Royal family, they are sitting there and be pretty.  I do bring them out to use in front of customers and visitors.   Only we know what are the good cheap tools, and what they are good for.  But in front of customer, I don't fight them, show them Fluke and they let me get on with my job.

[Cerebus]

I was going to think of something clever to go with a few excerpts from the site - but when I read this, the enthusiasm vanished...

DIRECTIONALITY: All audio cables are directional. The correct direction is determined by listening to every batch of metal conductors used in every AudioQuest audio cable. Arrows are clearly marked on the connectors to ensure superior sound quality. For best results have the arrow pointing in the direction of the flow of music. For example, NAS to Router, Router to Network Player...

... your wallet to our bank account.

[Cerebus]

I though Daddy would have a laugh, even if most of it currently goes over Sagan's head. Many of the 'stories' are very British, even Yanks may not understand them.

I laughed my arse off when Dave mentioned "Porton Down" as a shed. Clearly this is a troll book, indeed part of a comedy series for adults who were brought up on Ladybird books as children.

e.g. My favourite Ladybird book as a child Making a Transistor Radio. I wouldn't recommend an old TRF PNP design in nowadays it has to be said!

I think the subtleties of humour in the Old Dart go over Aussies heads maybe as much as it does the Americans?

The great thing with this book is it will still appeal to children despite the obvious to adults utter non Political Correctness. 

I haven't seen the 'Ladybird' book that Sagan and Dave got sent, but I presume it mentions the necessity of the shed to the British gentleman for having a crafty fag and a few pints of homebrew with his mates?

From the original Ladybird books I cannot recommend highly enough the "Ladybird Book of the Internal Combustion Engine".

[nowlan]

I thought the letter said something about pb swiss. Was looking forward to that, instead we got a pen?

[wblock]

What's wrong with these cheap Chinese multimeters? Of course, you shouldn't use it for measuring mains, the inside doesn't look very CAT II safe as printed on the top, and the cables don't have enough copper for 10 A, but otherwise it might be useful for reasonable accurate low voltage and resistor testing. Might even have a faster continuity tester than more expensive multimeters.

Watching the readings fluctuate on cheap meters is really annoying, but rather than throw it away, it would be good to stick in the glove box.  Too crappy for regular use, but better than nothing in an emergency.  (Are they called a "glove box" in Australia?  Or something colloquial like "wombat pouch"?)  There were some things on that meter that could have stood a little investigation, too.  Was the footprint around the COB for a QFP IC, or was it for a testing jig?  The layout of the backlight and display kind of looked like a standard 16x2 character LCD.  I also wondered if the solder on the current shunt might actually be filling a cut space to act as a fuse.

[Brumby]

Glove box is the term.

'Wombat' either means the animal or a person doing something silly or stupid.

There's also a thing called a 'wombat crossing' - which is just like an ordinary pedestrian crossing across the road, except that it is raised - making a long flat speed bump for traffic.


But back top the subject ... it's a glove box.

[sony mavica]

i love Swiss Army Knives its sad that i lost mine they are amazing

[G7PSK]

I think the picture of Roland sorting screws in his shed was of a typesetter.

[Cerebus]

'Wombat' either means the animal or a person doing something silly or stupid.

The word "wombat" is almost always preceded by the word "You". The equivalent English, especially London and the South east, usage is "You muppet!".

[Cerebus]

I think the picture of Roland sorting screws in his shed was of a typesetter.

The illustrations have clearly been re-purposed from the huge stock of artwork from the original children's Ladybird books - they must be a goldmine of humour if looked at with the right eye.

[rrinker]

 Just Google image search for Ladybird Books. It is indeed a gold mine of humor.

[Fred27]

I got a few of those Ladybird books for Christmas. They're excellent. Yes - I think it says that the pictures were taken from genuine books and just the text redone.

[Macman]

e.g. My favourite Ladybird book as a child Making a Transistor Radio. I wouldn't recommend an old TRF PNP design in nowadays it has to be said!

Mention of that book bring back childhood memories for me. When I was at primary school (about 11 years old) I made the regenerative radio from that book and took it into school and proudly showed it working to the other children in the class.  We were not allowed to bring radios in to school so the teacher confiscated it. The teacher didn't believe I made it because I was considered the dunce of the class.
Later I got called into the head masters office where I was asked about the radio and given it back.   

[f4eru]

The RF cable modem thingy is supposed to be a bidirectional amplifier.
In cable applications with broadcast and internet, there are often bidirectional amps in the network (sturdier ones).
This is done to compensate long lengths of cable.
Stably amplifying in both directions is not easy, it can quickly turn into an oscillator. This is why they took many precautions.... But there seems to be only one path, strange. Something on the other side of the PCB ?

[SL4P]

Everyone knows that signals are 'sourced' or 'sunk' at the appropriate intervals to create pulses of energy that often become 'sound' when modulated at audio frequencies.

To a novice, the technical concepts of sinking and sourcing can be literally replaced with sucking and blowing.  These are also terms familiar to the audiophool.

[SeanB]

What's wrong with these cheap Chinese multimeters? Of course, you shouldn't use it for measuring mains, the inside doesn't look very CAT II safe as printed on the top, and the cables don't have enough copper for 10 A, but otherwise it might be useful for reasonable accurate low voltage and resistor testing. Might even have a faster continuity tester than more expensive multimeters.

Watching the readings fluctuate on cheap meters is really annoying, but rather than throw it away, it would be good to stick in the glove box.  Too crappy for regular use, but better than nothing in an emergency.  (Are they called a "glove box" in Australia?  Or something colloquial like "wombat pouch"?)  There were some things on that meter that could have stood a little investigation, too.  Was the footprint around the COB for a QFP IC, or was it for a testing jig?  The layout of the backlight and display kind of looked like a standard 16x2 character LCD.  I also wondered if the solder on the current shunt might actually be filling a cut space to act as a fuse.

You all missed the view of the cut leads, showing the unmistakable sight of the white shiny inner of the wire, not copper but copper coated aluminium. this is showing up in all Chinese products built down to a price, as they seem to have gotten the ability to draw it reasonably reliably, and of course it is much cheaper than copper in material cost. Simplest test is the lighter method, where copper simply glows red but this droops, and steel is magnetic.

[ejeffrey]

In China it is normal to put the family name first, so Jianwei and Haibin are their given "first" names, and Song is their shared family/surname.

The way I have heard Jianwei pronounced is with the 'Jian' as in "Jean-Luc Picard".  Not sure how close that is to the way a native would pronounce it.

[kalleboo]

It's probably for the best the watch didn't turn on: A cheap smart watch often peddled on eBay uses a pairing app for Android or iOS that contains a backdoor that quietly connects to an unknown Chinese IP address

[station240]

That crappy multimeter had other issues Dave didn't mention. Most of the pins for the transistor tester socket weren't soldered, also a blob of solder on the plastic case under one end of the PCB.
I have a rather sturdy hammer to use on such products, so they don't fall into the wrong hands.

[SeanB]

That crappy multimeter had other issues Dave didn't mention. Most of the pins for the transistor tester socket weren't soldered, also a blob of solder on the plastic case under one end of the PCB.
I have a rather sturdy hammer to use on such products, so they don't fall into the wrong hands.

Just busy putting a new handle on the one I have, the old one broke........... Good thing is the hardware shop 50m away has a few spare ones in stock, for the price of $2. Now just have to do a little work on the fit and put a coat of paint on the handle and some furniture oil on the new Meranti handle.

[Cerebus]

In China it is normal to put the family name first, so Jianwei and Haibin are their given "first" names, and Song is their shared family/surname.

The way I have heard Jianwei pronounced is with the 'Jian' as in "Jean-Luc Picard".  Not sure how close that is to the way a native would pronounce it.

The J at the beginning is a mix between an English 'ch' sound and 'j' sound. That's a bit of guess though because there have been about 10 formal systems of romanization of Chinese and dozens of informal ones. Without knowing which is being used it's a bit of a crap shoot; but the suggested pronunciation fits a very common name and I happen to know someone with the same name.

[NiHaoMike]

Directional cables actually do exist. The truly directional ones have multiple layers of shielding and the outer layer only connects at one end. The idea being that end should connect to the part with a more direct ground connection.

[Dawanpi]

In China it is normal to put the family name first, so Jianwei and Haibin are their given "first" names, and Song is their shared family/surname.

The way I have heard Jianwei pronounced is with the 'Jian' as in "Jean-Luc Picard".  Not sure how close that is to the way a native would pronounce it.

The J at the beginning is a mix between an English 'ch' sound and 'j' sound. That's a bit of guess though because there have been about 10 formal systems of romanization of Chinese and dozens of informal ones. Without knowing which is being used it's a bit of a crap shoot; but the suggested pronunciation fits a very common name and I happen to know someone with the same name.

The family name is Song https://en.wikipedia.org/wiki/Song_(Chinese_surname)
"Jianwei" and "Haibin" are given names. Both are very common in China.

[Neilm]

Dave should have kept that meter. It was marked 600V CATII which I think is a 4kV transient superimposed on the 600V. Could have used the high speed camera to film the explosion.

[apis]

In China it is normal to put the family name first, so Jianwei and Haibin are their given "first" names, and Song is their shared family/surname.

The way I have heard Jianwei pronounced is with the 'Jian' as in "Jean-Luc Picard".  Not sure how close that is to the way a native would pronounce it.

The J at the beginning is a mix between an English 'ch' sound and 'j' sound. That's a bit of guess though because there have been about 10 formal systems of romanization of Chinese and dozens of informal ones. Without knowing which is being used it's a bit of a crap shoot; but the suggested pronunciation fits a very common name and I happen to know someone with the same name.

The family name is Song https://en.wikipedia.org/wiki/Song_(Chinese_surname)
"Jianwei" and "Haibin" are given names. Both are very common in China.

I've heard it's common to have the same family name in China but the surnames given name is often more unique?

[apis]

I recently got several new Victorinox knifes, they really are great quality. When I was very young and very stupid we tried to deliberately break the blade on one but failed, it probably can be done but it survived a lot of abuse. I conjecture the most common failure mode is having it stolen or forgetting it somewhere (or confiscated by airport security).

[Macbeth]

I recently got several new Victorinox knifes, they really are great quality. When I was very young and very stupid we tried to deliberately break the blade on one but failed, it probably can be done but it survived a lot of abuse. I conjecture the most common failure mode is having it stolen or forgetting it somewhere (or confiscated by airport security).

I agree with this. My most prized possession at one point as a child was a Victorinox pen-knife that had EVERYTHING, eyeglass, rule, drivers, scissors, can opener, the lot. The electrician had left it behind and I figured "Finders Keepers" as he left it so long... and nobody noticed...

Unfortunately my mum found me showing it off to all the kids and strangely enough the electrician turned up soon after claiming he left a tool behind, and I had to sheepishly give it up 

Oh actually I remember another one around the same time - A continental lorry driver overturned his truck and all the police were out in force at the accident scene. I spotted amongst the truckers debris a very nice locking switchblade, which happens to carry an absurd mandatory sentence for carrying in the UK (I didn't know that when I was 10). I purloined it and sadly a copper spotted me and got it back. While the trucker probably got prosecuted for falling asleep at the wheel, he probably ended up in prison for 5 years for having the perfectly reasonable safety locking blade in his kit of tools at the time and it having no bearing on the accident whatsoever.

Sadly all the really good multi-tools will have locking blades, but a perverse lacuna in the UK knife law is that makes them illegal.

[apis]

Sadly all the really good multi-tools will have locking blades, but a perverse lacuna in the UK knife law is that makes them illegal.

Yeah, some knife laws are dumb. They had some trouble in Denmark recently, politicians had made further restrictions to their knife laws and suddenly people were sentenced to jail for having multi-tools in their car... And recently in Sweden prosecutors took a knife case all the way to the supreme court (woman had a folding kitchen knife in her bag when walking home from a friend, she had helped with preparing food for a party). Luckily they responded with a very reasonable list of when it is legal to carry knifes. Knives are tools, well pocket knifes anyway, and should be legal. A crochet needle is probably just as dangerous if someone is intent on causing harm, not to mention fists and legs, and people in general.

[Macbeth]

I have an inkling that those knife laws don't apply to "our new friends" - Saudi curved blade head-lopping scimitars and janburi daggers for example will be dealt with "diversity" and "cultural needs" taken in to account.

[Fungus]

It's probably for the best the watch didn't turn on: A cheap smart watch often peddled on eBay uses a pairing app for Android or iOS that contains a backdoor that quietly connects to an unknown Chinese IP address

Lucky for us the $1000 USA built ones don't connect to random USA IP addresses, eh?

[Fungus]

I conjecture the most common failure mode is having it stolen or forgetting it somewhere (or confiscated by airport security).

I was in the UK last week and I had my minichamp with me. I stupidly forgot to put it in my checked bag on the way back so I was worried they would confiscate it. I had it in my pocket and I put it in the tray with my keys and loose change. It got through two security checks just fine (technically it's not illegal to carry it, but...)

On the other hand: Both metal detectors I went through made a beep but on the other side they didn't check me for metal or make me go back through the arch. Both times they just swabbed the palms of my hands for chemicals. What's that all about? Do I look like a bomb-maker or drug smuggler?  The beep at the arch was obviously somebody pressing a button, not metal detection.

[apis]

I've heard it's common to have the same family name in China but the surnames are often more unique?

Define surname and family name.

Ah, I meant given name . Here it's common to have the same given name but not so common to have the same surname/last name. Someone told me it's the other way around in China, not sure if it's true?

[apis]

On the other hand: Both metal detectors I went through made a beep but on the other side they didn't check me for metal or make me go back through the arch. Both times they just swabbed the palms of my hands for chemicals. What's that all about? Do I look like a bomb-maker or drug smuggler?  The beep at the arch was obviously somebody pressing a button, not metal detection.

I've heard they can be set to beep at random when people pass through. It might have been to get a truly random sample of people to swab?

[Fungus]

On the other hand: Both metal detectors I went through made a beep but on the other side they didn't check me for metal or make me go back through the arch. Both times they just swabbed the palms of my hands for chemicals. What's that all about? Do I look like a bomb-maker or drug smuggler?  The beep at the arch was obviously somebody pressing a button, not metal detection.

I've heard they can be set to beep at random when people pass through.

It certainly wasn't because I had any metal on me.

It might have been to get a truly random sample of people to swab?

Twice in one day? Could be random.... but I'm wondering if it was because I was wearing baggy army trousers with lots of pockets. 

OTOH they're not supposed to profile based on appearance, right? That would be security failure 101.