EEVblog #964 - Mailbag

[EEVblog]

SPOILERS:
Educational kits from
http://tronclub.com/

Electro-permanent magnet for UAV's and drones from NicaDrone
http://nicadrone.com/index.php?id_product=13&controller=product

Cisco VOIP phone teardown

1980's GE Cordeless phone teardown

Open source USB charger:
http://www.bloguetronica.com/2016/12/modulo-carregador-usb-ucharge-rev-1.html

STM32 Development board:
https://www.tindie.com/products/maxtch/arduino-compatible-stm32f103c-development-board/

Max Chan is for hire:
https://en.maxchan.info/

[Kelbit]

Is that the new EEVBlog meter we're seeing? Looking forward to the the full video on it.

[Brumby]

That electro-permanent magnet is very neat.

[elgonzo]

You look for something that will enthuse your young one for mechanical engineering? Get an educational IKEA furniture kit.

You are interested in wood-working, but aren't sure whether you should invest much in tools or whether your interest will last longer? Why not start with a reasonable priced educational IKEA furniture kit?

You just want to build some cool thing? Want to share it or gift it to friends?
Something convenient, a gift that keeps on giving? Get an educational IKEA furniture kit.

I love these kits. They are sooo educational...
In all seriousness, many of these kits teach as much about electronics (or programming, for that matter) as IKEA furniture teaches about mechanical engineering and "wood"working...

[loomx]

@Dave:
Regarding the LowZ-Mode on the BM235: I noticed this "error" myself and got in contact with the German distributor Marco (Welectron.com). He told me that he got in touch with Brymen and this is the intended behaviour (and has been through all firmware versions). For whatever reason,  they don't include that in the specifications. He mentioned that they didn't know if this might be changed in the future or if Brymen might just change the specs.
Marco provided me with the test report attached.
I should have reported that earlier (and possibly prevented that return) but at least this mailbag gave me a reason to register on the forum . Sorry about that

[McBryce]

The "upside down button" design on the Cisco phone is quite common for this type of application. It avoids the button being damaged by people slamming the phone or beating on the button with their finger (as is very common). The pressure on the button can only come from the spring so it's always the same and the expected lifetime can be guaranteed. The hairpin spring ensures that the spring can't get over or under extended over its lifetime.

McBryce.

[technix]

Thanks for starring my item, although it took an exceptionally long time... (I will just keep marking my packages with the words "From Shanghai With Love" so you can tell my packages from Chinese Ebay items)

I have got a Arduino-likecore ready but there are still problems not sorted out. Schematics are available for those who are brave enough to explore though.

[iaeen]

Normal service is resumed, WooHoo!

The force is strong with the tronclub kits. I'm seriously considering signing up... Thanks for sharing!

Also looking forward to seeing the "super secret" multimeter come out of hiding. You're killing us with all these teases.

[Fungus]

The "upside down button" design on the Cisco phone is quite common for this type of application. It avoids the button being damaged by people slamming the phone or beating on the button with their finger (as is very common).

Why do people do that? Is it just hollywood or do people do it in real life when the connection is lost? There's absolutely no way it will reconnect you or fix anything. 

With practice you can bang on the 'hook' switch to dial the number. Just bang it N times quickly/rhythmically to dial the number N, eg. bang it twice to dial a '2'. Pause between each number.

The reason it works is because that's how those old mechanical dial phones dialed the numbers. The dial would simply make/break the switch contact N times as it returned from number N. You're just emulating that.

It's quite easy with a bit of practice and totally defeats those old dial locks, leaving no trace. 



Edit: Aren't you supposed to put the lock on the number '1'? Putting it on '0' achieves nothing - you can still turn the dial.

[slicendice]

That Tron-Club kit subscription looks really nice. And as you said, it's bargain.

On their site they claim you'll get over 252 circuits per year to keep you occupied. That is AWESOME!

Think I might start subscribing for both kits and build circuits with my kids.

Hope Tron-Club will become successful and stay in business for a long time.

[nctnico]

Just a remark about the Cisco phone teardown and the comments about the copper pattern on the PCB: having an even pattern distribution on a PCB is still important nowadays. Some manufacturers (like Eurocircuits) will break your balls if you have large empty (=no copper) spaces on a design because it will make it harder for them to produce the PCB reliably. See: http://www.eurocircuits.com/Plating-index

[sleemanj]

With practice you can bang on the 'hook' switch to dial the number. Just bang it N times quickly/rhythmically to dial the number N, eg. bang it twice to dial a '2'. Pause between each number.

An interesting fact, here in New Zealand the order of numbers on a pulse dial phone was reversed, to dial 1, there were 9 pulses!  There is no real conclusive answer as to why that happened, various opinions range from protecting local manufacture, to iust "that's just what the guy in charge decided on the day". 

I remember i first learned about this oddity when I bought my first modem and there was a note about pulse dial (ATDP)  in NZ, i don't remember how it was worked around in the modem now since by that time we had been tone dialling for a few years, push button phones having been installed at home to much amazement in, i think, 1988, maybe 89

[capt bullshot]

Edit: Aren't you supposed to put the lock on the number '1'? Putting it on '0' achieves nothing - you can still turn the dial.

Yes, but you can't dial "0", which keeps you from long distance calls. In former times local calls were kind of flat (pay per call, not per seconds), but long distance calls were really expensive (like pay per every 20 sec or 40 sec)

[Fungus]

With practice you can bang on the 'hook' switch to dial the number. Just bang it N times quickly/rhythmically to dial the number N, eg. bang it twice to dial a '2'. Pause between each number.

An interesting fact, here in New Zealand the order of numbers on a pulse dial phone was reversed, to dial 1, there were 9 pulses!

Weirdos 

In theory they have to keep the exchanges backwards-compatible forever so it will still work. I haven't got a phone here to try it but I did it about six months ago as a party trick.

nb. I actually know why they bash on the hook in the movies. In the very old days the operators had lights on their consoles and it made the light flash to get their attention. The operator would then connect to your line and you could talk to them...)

I remember i first learned about this oddity when I bought my first modem and there was a note about pulse dial (ATDP)  in NZ, i don't remember how it was worked around in the modem

 

Yes, modems would have been fun. You'd have to do math on the number to be able to dial it.

[Fungus]

Edit: Aren't you supposed to put the lock on the number '1'? Putting it on '0' achieves nothing - you can still turn the dial.

Yes, but you can't dial "0", which keeps you from long distance calls.

You'd have to put it in the '9' for that. 

[PeterL]

@25:00
If you order a pcb at eurocircuits, you can preview your order in their 'PCB visualizer'. On their they show you a simulation of the copper plating, and also calculate a 'Copper Plating Index'. It shows you if you can expect trouble with regards to the plating.

And nowadays you won't run into trouble fast, but I have had a few boards that were oversized for mechanical reasons, on which this plating index was to low.

Anyway, if you want to learn more about copper plating this tool if really helpful.

[slicendice]

Edit: Aren't you supposed to put the lock on the number '1'? Putting it on '0' achieves nothing - you can still turn the dial.

Yes, but you can't dial "0", which keeps you from long distance calls.

You'd have to put it in the '9' for that. 

00358 is the number to dial if calling to Finland, I don't see any 9 in there..besides that lock makes sure the whole dial won't move at all. If it'd move then it'd be possible to call anywhere anyways.

[Fungus]

Yes, but you can't dial "0", which keeps you from long distance calls.

You'd have to put it in the '9' for that. 

00358 is the number to dial if calling to Finland, I don't see any 9 in there..besides that lock makes sure the whole dial won't move at all. If it'd move then it'd be possible to call anywhere anyways.
[/quote]

Does this image help? The important part is the metal bit which your finger hits when you turn the dial.

(which is actually a totally brilliant design BTW. Whoever thought of that is a genius)

[Zbig]

nb. I actually know why they bash on the hook in the movies. In the very old days the operators had lights on their consoles and it made the light flash to get their attention. The operator would then connect to your line and you could talk to them...)

I always wondered why there was a button on landline phones that generated brief "on hook" - "of hook" pulse and was labelled "Flash". Didn't seem to do anything useful yet pretty much every keypad-based phone around here had one. Finally, the mystery is solved! Thanks

BTW, regarding slamming of the "hook" contact - we had Siemens sets in our office few years ago that had optical (IR-based) sensor; no moving parts at all. It was rather funny watching people swirling their fingers around the headset cavity when they were trying to break the connection in order to make a new one without actually putting the headset down and back up again. Looked kind of like they were stirring an invisible cup of tea with their fingers.

EDIT:
After jogging my memory a little, now I remember those "Flash" buttons weren't really that useless, after all. At least on some exchanges over here, they were used, in sequence with DTMF keys, for functions like switching to waiting call and such. At least now I know the origin of the "Flash" label.

[Co6aka]

Hey Dave, you actually pronounced it right!!!    "Nee-ka-ra-gyou-wah"  Have a hear here: 

[Cerebus]

Yeah, that Cisco 7961. The hook switch is known, possibly even notorious, for being 'sticky' after the phone has been in service for a while. Phone rings, you grab the handset and the phone carries on ringing.

One reason for having the hook switch engineered the way that it is that they needed a PCB at that point anyway. On that board there's a LED used as the 'message waiting' light. The LED connects to a light pipe in the cradle that shines onto another light pipe that goes all the way through the top of the handset. It actually works really well and is easy to spot.

There's, I suspect, quite a lot of DSP goodness hidden inside the Cisco branded chip and a fair bit of CPU grunt as it has to have the horsepower to run end-user 'enterprise' Java applications on the phone on top of all the basic IP phone stuff. The phone's firmware package, if unzipped, contains separate firmware for the DSP. The DSP side of things is used to handle the various voice, and in other models in the range, video codecs and to run the genuinely excellent hands-free capability of the phone. From memory the CPU is a MIPS 32 implementation. Oh and there's a 2 port ethernet switch built in as well so that your PC and phone can share a single wall socket.

[boffin]

Is it wrong that I made a bowl of popcorn to watch mailbag ?
Do I need to join a support group?

[Brumby]

Not at all.

Just make a bit extra next time and share it around...

[Brumby]

With practice you can bang on the 'hook' switch to dial the number. Just bang it N times quickly/rhythmically to dial the number N, eg. bang it twice to dial a '2'. Pause between each number.

The reason it works is because that's how those old mechanical dial phones dialed the numbers. The dial would simply make/break the switch contact N times as it returned from number N. You're just emulating that.

It's quite easy with a bit of practice and totally defeats those old dial locks, leaving no trace. 

Yes - with pulse dialing it doesn't take much to learn how to do it - and reliably.  Never had to use it on "locked" phones though.  I just did it so I knew I could.

[EEVblog]

@Dave:
Regarding the LowZ-Mode on the BM235: I noticed this "error" myself and got in contact with the German distributor Marco (Welectron.com). He told me that he got in touch with Brymen and this is the intended behaviour (and has been through all firmware versions). For whatever reason,  they don't include that in the specifications. He mentioned that they didn't know if this might be changed in the future or if Brymen might just change the specs.
Marco provided me with the test report attached.
I should have reported that earlier (and possibly prevented that return) but at least this mailbag gave me a reason to register on the forum . Sorry about that

Thanks.
Manual now updated.