[GreenKeys] rotary dial telephone specs

[Norm]

What I remember was that we had AE dials, and there was a cam in the dial that would spin, Which made the percent 50% make 50% break, the speed was at 10 P/S and was controlled by a disc ( something like a brake shoe) and adjusted by how much tensen was on the throwout springs touching the brake shoe, the space between the digits was the adjustment of the B or the C relay in the selector at the Central Office don't remember, but I think it was the B ( slow to release relay).

Norm
WB7WEQ
    
----- Original Message ----- 
From: gil at baudot.net 
To: Sam Hallas ; aaa-greenkeys 
Sent: Monday, June 03, 2013 2:23 PM
Subject: Re: [GreenKeys] OT - rotary dial telephone specs


Sheesh, a lot of off-list replies to this --thanks all.  I'll reply on-list with a summary, as I think this thread might appeal to quite a few telephone folks on greenkeys:


So it seems that 10-pulses-per-second (about 100ms period for break/make) was typical, with the break time being perhaps as low as 50ms or so (with 50 ms make), to about 66ms (with 33 ms make).  Some exchanges may have run faster.



With a possibly-unadjusted dial regulator, combined with maybe some goop or grit in the mechanism, the dialing pulses probably varied a lot, so I guess it stands to reason that the exchanges would allow a fair amount of latitude on the dialing waveform.


I wonder what the exchanges considered the minimum inter-digit make time?  In my arduino program, I place no constraints on the break time, but look at the make time between pulses as about 400-ms max before I consider it to be an inter-digit pause.  I have not tested how quickly I can dial 1-1 (as Jim pointed out) to look for the minimum empirical pause, but my test setup is currently disconnected.


I did notice just how noisy the dialer switches were.  I am used to debouncing a typical pushbutton with a delay of about 5ms, as they seem to settle pretty quickly, but the dialers were incredibly-noisy switches, with lots of high-frequency make/break stuff going on for almost 10 ms.  I could easily improve this but lowering the impedance into which the switch feeds, and a simple RC filter, but that would defeat the purpose of the debounce-in-software experiment.


Anyway, fun stuff.  In these days of disposable technology and standards in the software world that change fluidly every few months, it is really nice to find that my 80- and 90-year old phones not only pass audio on today's landlines, but dial flawlessly as well.  Of course, that's why we all like teletype machines as well.


gil






gil smith
greenkeys moderator
gil at baudot.net




  -------- Original Message --------
  Subject: Re: [GreenKeys] OT - rotary dial telephone specs
  From: Sam Hallas <s.hallas at ntlworld.com>
  Date: Mon, June 03, 2013 1:06 pm
  To: gil at baudot.net, aaa-greenkeys <greenkeys at mailman.qth.net>

  gil at baudot.net wrote:
  > So my question is what was the design standard for a dial phone's
  > pulse-widths? They both work just fine on my Centurylink landline, and
  > I dialed up my cell phone and left myself a message with each phone.
  > Perfect dialling and audio sounded good in both directions too.

  It depends on the switching system, but the timing for the Strowger 
  step-by-step switches used here in the UK was 66 ms break to 33ms make 
  at 10 pulses per second.

  I can't remember what the inter-digit pause is supposed to be. I'd have 
  to look it up.

  Cheers,
  Sam





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