Re: Ep.3 - A Very Special Too Damn Late Show

On Wed, 20 Jun 2007 00:16:59 GMT, mroberds@xxxxxxxxxxxxxxxx wrote:

Jasper Janssen <jasper@xxxxxxxxxxxx> wrote:
My local exhange has stopped accepting pulse-dialing.

This will probably eventually happen in the US as well. When pressed,
$TELCO will probably cite the need to still support older alarm systems
and such that may still use pulse dialing. What they are actually doing
is waiting for everyone who will complain if their 500 set stops working
to die.

http://www.telefoonmuseum.com/kunststof/t65_tdk/ <- that one, to be exact.

What's that round thing at the lower right? Hold? Lamp that blinks on
ringing? I note that the buttons appear to have the DIN 1451 font, and
also don't have any letters on them.

It's the grounding button, this was back when NL telephones were 4-wire
devices rather than two. a, b (as normal), EB (ringing voltage), and
Ground. EB was usually connected to b inside the socket, making the phone
on that socket ring, but could of course be turned off by undoing that as
well. The arrangement was also routinely used to arcanely wire two sockets
for two-telephone use in such a way that both phones would ring but if
either was off-hook, the other wouldn't be able to listen in.

The ground wire was only used (AFAIK) for communication to a local PBX, by
shorting one or both (I forget) of a and b to GND as a signal. That's what
the button does. The GND was also used to detect the 'cost-tick' -- a
pulse of 'lectrickery that would appear on your line every time a 15
guilder-cent fee was charged to your account, which happened more or less
quickly depending on local/national/international etc. The pulse would be
on a and b simultaneously and only detectable by comparing with GND. The
advantage of the tick system as opposed to charging-by-the-second is that
you could make payphones with charging schedules actually related to the
actual cost of a call very easily, as well as cheap tick-counters for
shared usage situations.

All the *65 models (including the T65 table model and wall-mounted and
in-built models etc) had the grounding button integrated. A triplet
exchange model (
http://www.telefoonmuseum.com/kunststof/t65/t65_bestanden/image044.jpg )
would have two buttons and a light, which could be used somehow to summon
one of the other two phone users if you happened to pick up a call meant
for them, and may have been the first time the public at large was allowed
to have (and by have I mean rent, buying wasn't an option yet) more than
two phones. Unfortunately the one I used to use in situ had the
summon-other-phones bit broken, and although I do have a complete system
with 3 phones hardwired to (mostly) included wall junction boxes, and the
exchange, I've never had that one operational. And each phone has a 6-wire
cable running to it.

Jasper
.

Relevant Pages

  • Re: detecting gnd
    ... connected given that I want to power the test board from the socket. ... GND then it contributes to the GND plane and vice versa for VCC. ... Sure you can do this with single PLD! ...
    (comp.arch.fpga)
  • Re: How to gerate a pulse it width 500 -700 picosecond?
    ... >>How to gerate a pulse it during time is 500 picosecond and one times ... > View in Courier: ... > GND ...
    (sci.electronics.design)
  • Re: Contact Closure to TTL
    ... >> GND ... >>The longer you hold the button down the longer the pulse. ... > admirably and made me laugh. ... <AOL> ...
    (sci.electronics.design)