Telephone exchange from scratch

Various DIY telephone exchange machines, large and small

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How many stepping switches are needed to route calls between old rotary-dial telephones? Let's see.

All right, let me explain, why I made this thing.

1. It has historical meaning. Old rotary phones need to be connected to something called telephone exchange. In early times it was a huge piece if machinery hidden in machine room of local telephone exchange office. This device encourages people to learn more about telephone exchange equipment history.

2. It reuses old rotary dial phones. A lot of them are wasted in antique shops and junkyards. This device shows how to make them usable again.

3. It is secure. Sometimes one needs extra privacy (for busyness needs or I do not know what). This setup requires no computer components to work, otherwise one need to do firmware expertise to ensure there is no backdoor or such. (I believe that old hardware is more secure, because it has less complexity in it. We shall not update everything we have to make it more secure. No. We have to understand the technology to make it more secure/private. And less complex technology is easier to understand).

4. It is reliable to some extent. Stepping switch is a weak point that needs maintenance, but phones themselves are pretty thick and hard to break apart, also easy replaceable.

I should warn you that this Cadr-o-station device is a multi-conference one. That is, all phones are always connected together. No wonder, that only one stepping switch is needed here. It is used to send buzzer signals. If it fails, one can disable it, and phones will be still usable.

By the way, there is an long read article for the International Journal of Proof of Concept or GTFO issue 21 waiting for its readers.

There is another article on single page specially crafted for PagedOut magazine lead by Gynvael Coldwind. I hope he will recover from disease and publish it eventually in issue #3.

  • 1 × Stepping switch of any kind
  • 2 × Relay with 24V coil
  • 16 × Various 12V relays for logic circuitry
  • 2 × Power Transformers
  • 3 × Fuses in various places

View all 8 components

  • Log #2: POC or GTFO article is out!

    dearuserhron04/12/2022 at 00:51 0 comments

    Two good news.

    1. The International Journal of Proof of Concept or Get The F... Out Issue 0x21 is now available in PDF format (pocorgtfo21.pdf) for everyone who is interested. This is a masterpiece collection of articles on computer security, hacking, reverse engineering tricks and such stuff. There is something that makes me tick about this magazine. I am trying to read each article very carefully, and I was really waiting this issue to come out (especially knowing that it will contain long read about phones). - see contents of each issue of this magazine - main mirror

    2. The Cadr-o-station device is now have new home - it is now part of b4cksp4ce hackerspace in Saint Petersburg, Russia. The space inhabitants are now trying to make use of it and add missing features to it. Good luck, guys.

  • Log #1: Watch THIS

    dearuserhron09/03/2021 at 19:06 0 comments

    This is CADRSTATION. Special purpose old landline phone exchange for small households and hackerspaces. It requires only one rotating stepping switch. There is a difference compared to other exchanges: here all telephones are connected together all the time and talk to each other in a big multi-conference style. The rotating switch is used to send ring signals. Optional external connection to the city phone socket is planned.

    It bears CADR hackerspace logo, because it was assembled and tested there.

    And here is schematics (ask me, I will tell you more):

View all 2 project logs

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Keri Szafir wrote 12/13/2022 at 10:19 point

Nice little exchange. I got interested in old phone switching systems after watching ConnectionsMuseum and This Museum Is Not Obsolete. Got a bunch of pulse-dialed phones that I'd like to restore at some point and put to a good use. Looking for a stepping switch.

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dearuserhron wrote 12/18/2022 at 23:49 point

I got mine on Try searching ebay or something. There should be uniselectors.

Sam LMNC is a British national treasury, I think.

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0xCAFEAFFE wrote 12/12/2021 at 19:47 point

this is insane! i fucking love it :D

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