EEVblog #964 - Mailbag

[EEVblog]

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

Thanks
Never had a manufacturer complain about this before.
Incredibly common to have little copper on your outer layers when you are using internal ground planes.

[kalleboo]

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". 

Sweden also has a slightly "modified" pulse-dialing system. It's not reversed, but the 0 is before 1 rather than after 9. So 0 is one click and 1 is two clicks (and so on).

[Dave]

To demagnetise a ferromagnetic material, you need to repetitively drag it through progressively smaller hysteresis loops (see image).
The flux inside the magnetic circuit goes through zero many times during that process, therefore the metal that is stuck to it gets released and grabbed again multiple times, making the noise as it repetitively bangs against the magnet.

F*cking magnets, how do they work?

[McBryce]

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.

The answer is in the picture you included, if it was on 1 you couldn't call the emergency services "999" in the UK. Putting it on 0 means you can only call local numbers or the emergency services.

I don't think the "banging out the number trick" works in Germany since they went to digital telephone exchanges, the new exchanges only react to DTMF dial tones.

McBryce.

[Fungus]

The answer is in the picture you included, if it was on 1 you couldn't call the emergency services "999" in the UK. Putting it on 0 means you can only call local numbers or the emergency services.

I never thought of that.

But still, putting it in the zero only works psychologically. You can still dial a '0' but you turn the dial using the lock instead of putting your finger in the zero hole.

I don't think the "banging out the number trick" works in Germany since they went to digital telephone exchanges, the new exchanges only react to DTMF dial tones.

It should still work. It has to be backwards compatible with old telephones.

(Unless they forced everybody to change their phone, which is possible I guess)

[Terrius]

I look forward to the exploding capacitor video! Though I think a small portion of the "fun" might be lost in not being there to experience the smell! No better smell (hmm or perhaps nothing more awful) than old electronics burning!

That Tronclub thing is really cool, Does anyone know if they will only send the items once per month? or if once you finish one project you can pay for the next month  and get them to send the next kit?

[McBryce]

The answer is in the picture you included, if it was on 1 you couldn't call the emergency services "999" in the UK. Putting it on 0 means you can only call local numbers or the emergency services.

I never thought of that.

But still, putting it in the zero only works psychologically. You can still dial a '0' but you turn the dial using the lock instead of putting your finger in the zero hole.

I don't think the "banging out the number trick" works in Germany since they went to digital telephone exchanges, the new exchanges only react to DTMF dial tones.

It should still work. It has to be backwards compatible with old telephones.

(Unless they forced everybody to change their phone, which is possible I guess)

Nope, the lock stopped it from going far enough. It hit that metal hook thing, so it dialed a 9 instead of a 0 if you dialed with the lock on.

The exchanges aren't backwards compatible. As far as I can remember they announced at some stage that the old phones wouldn't work anymore. At the time you only had the choice of Deutsche Telekom as service provider and the phone itself was part of the contract, so you could go in and swap it for a new one.

McBryce.

[bktemp]

The exchanges aren't backwards compatible. As far as I can remember they announced at some stage that the old phones wouldn't work anymore. At the time you only had the choice of Deutsche Telekom as service provider and the phone itself was part of the contract, so you could go in and swap it for a new one.

If you still have the old analogue phone line and haven't upgraded to ISDN or DSL, the old pulse dial phone should still work. I know somebody who used one until last year.

[Zbig]

The exchanges aren't backwards compatible. As far as I can remember they announced at some stage that the old phones wouldn't work anymore. At the time you only had the choice of Deutsche Telekom as service provider and the phone itself was part of the contract, so you could go in and swap it for a new one.

They are - to some extent - or at least they could be, if needed. I'm not sure if that's still the case in Poland (don't have a landline), but you could still use pulse dialing alongside DTMF here for ridiculously long into 21th century. Might or might not be related to low average wages and inability and/or unwillingness to get a new phone (you bought your own on the open market here) for considerable part of the userbase.

[Fungus]

Nope, the lock stopped it from going far enough. It hit that metal hook thing, so it dialed a 9 instead of a 0 if you dialed with the lock on.

I haven't got one to try but I find hard to believe it wouldn't dial a zero if you turned the dial until the lock touches the metal hook. The lock only prevents a couple of mm of travel at the most. That's no worse than holding your finger at the wrong angle.

[McBryce]

The exchanges aren't backwards compatible. As far as I can remember they announced at some stage that the old phones wouldn't work anymore. At the time you only had the choice of Deutsche Telekom as service provider and the phone itself was part of the contract, so you could go in and swap it for a new one.

If you still have the old analogue phone line and haven't upgraded to ISDN or DSL, the old pulse dial phone should still work. I know somebody who used one until last year.

I think it may depend on where you live too. I don't think it's possible to have an analogue line anymore in Cologne.

@Fungus: That is enough to stop the 0 from working, or at least it was with the phone we had at home when I was a kid  It's only about a 4 or 5mm difference, but it hangs over the number 9 hole and definitely didn't let you get a zero. My father had pretty fat fingers and regularly dialed wrong numbers because of it. My girlfriend of the time lived relatively near to us, but we were at the county border and she had a different area code. 

McBryce.

[twice11]

I look forward to the exploding capacitor video!

These Rifa capacitors are known as "Knallfrosch" ("firecracker") in German vintage HiFi forums. Most HiFi enthusiasts don't share the excitement about them exploding, though.

[bluetopia]

I've signed up for TronClub, I've been wanting to get back into electronics again. (Also Hello everyone!)

When I heard they were based out of Canada, I assumed that they'd be pulling the same trick that my VOIP provider does; primarily operates in Canada, but charges everything in USD.  But as it turns out, it was $25 CDN for me. Score!

The only thing I'm not particularly happy with is the fact you can't set up both the beginner/advanced subscriptions easily on the site.  Couldn't figure out how, and I wanted to get the microcontroller starter kit as well. But at least they will let you swap between the two series without issue; you receive whatever your next kit is in the chosen series, and they keep track of which kits you've received, so you shouldn't receive the same kit twice.

Once I get my first kit, I'll be flipping it to get the first micro kit as well.

[Fungus]

@Fungus: That is enough to stop the 0 from working, or at least it was with the phone we had at home when I was a kid  It's only about a 4 or 5mm difference, but it hangs over the number 9 hole and definitely didn't let you get a zero. My father had pretty fat fingers and regularly dialed wrong numbers because of it. My girlfriend of the time lived relatively near to us, but we were at the county border and she had a different area code. 

I would have expected the switch point to be a bit further back (for people like your father). Maybe it varies between phones. I don't have any to test so I bow to experience.

[McBryce]

I must ask my father if he still has that old phone. It would make a quick but interesting teardown. Maybe I could convert it to DTMF to use as a cool retro device.

McBryce.

[bktemp]

I must ask my father if he still has that old phone. It would make a quick but interesting teardown. Maybe I could convert it to DTMF to use as a cool retro device.

If the teardown is too quick, try understanding how everything works (the schematic should be available for most phones, because there aren't many different models). A lot of clever engineering went in designing those old phones to make them simple and reliable.

[McBryce]

I doubt it contained anything more than switches and a bell. It looked something like this.

I'll be back home (Ireland) in a few weeks and go looking.

McBryce.

[bktemp]

It is a bit more complicated than just a switch:
http://macao.communications.museum/eng/exhibition/secondfloor/MoreInfo/2_6_1_DTMF.html
http://www.britishtelephones.com/dial1.htm

[McBryce]

It is a bit more complicated than just a switch:
http://macao.communications.museum/eng/exhibition/secondfloor/MoreInfo/2_6_1_DTMF.html
http://www.britishtelephones.com/dial1.htm

Cool, that will make an interesting teardown (if I can find it).

McBryce.

[rrinker]

 I have that exact model Cisco phone on my desk at work. Yes, we still use old crap. About half of them got stuck buttons, those were replaced by new models. The ones that never got stuck, pretty much never will. Yes, they are super slow to boot up - the processor is really too slow to run all that java overhead garbage. Once running it's generally fine but you really can see the screen refresh when you do something that calls up info on it.

[nctnico]

I must ask my father if he still has that old phone. It would make a quick but interesting teardown. Maybe I could convert it to DTMF to use as a cool retro device.

Here is a reverse teardown from James May 'The Reassembler':

[crashputer]

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.

I don't know how other countries built their telecom systems, but in America it was entirely possible to dial the phone on old-style analog systems, even with the lock installed. The tapping seen in classic movies is the same as dialing the rotor -- tapping the receiver 10 times would dial the operator, or you could tap a complete telephone number by using the corresponding number of taps with about a second pause between numbers.

Edit: Apparently 20 people already answered this before I did, and more, haha.