Crossbar telephone exchange demo

I have built a crossbar telephone exchange demonstrator using an Ericsson crossbar switch and an Arduino microcontroller. This video shows its operation and provides an explanation of the mechanism and its control.

[@brianjonesg8aso403]

I fitted these as PABX for Serk Services in Redditch. Marvelous piece of kit worked 100% out of the box, far superior to Strowger. Fairley weird operator's console. This worked for a good 20 years with minimal maintenance.

[@amartini51]

Thank you for this explanation - I've been trying to understand how crossbar exchanges worked for a while now. You made everything very clear!

[@AenesidemusOZ]

I'm old enough to remember what a pain in the butt crossbar relays were to adjust. While doing it, I used to think back fondly to step-by-step (Strouger) switches 😂

[@wimderkinderen1952]

It took me quite a while to get my head around the operation of a crossbar switch. It is inherently more complicated than Strowger. But the story goes that they required less maintenance?

[@AenesidemusOZ]

@wimderkinderen1952 crossbar switches took up a lot less space per extension and used a lot less power. Cleaner, faster, and quieter, too. But they would go out of adjustment (contacts and wires) at the drop of a hat - or minor change in temperature and humidity; airconditioning was a LOT more important with crossbar.

[@etmax1]

I loved this, it was very nostalgic, and while I didn't get into telephony until the early 80's when the company I worked for was using reed switch crosspoint switches in their larger exchanges and SCR crosspoint switches in their PABX's. I also loved your almost totally non-computer based (torch and camera) presentation method.

[@wimderkinderen1952]

Thanks. There is more telecom stuff on my Channel.

[@manuelzelaya7527]

Wonderful explanation, it makes me feel young again remembering the sound of the crossbar switch, thank you

[@ruudshangout]

De crossbar en hefkiezers zijn mij bekend, maar wat mooi om ze in jouw demo setups te zien. Dit is inderdaad de mooiste techniek die er bestaat. Zelf heb ik dit spul helaas nooit kunnen bemachtigen, dus deze video’s maken het weer goed. Een prachtig YT kanaal dit.👍

[@algorithminc.8850]

Love the old electronics ... many good ideas for modern bits hidden away back in the days of people actually thinking. Thanks. Great video. Look forward to checking out your channel. Subscribed. Cheers ...

[@wimderkinderen1952]

Very true! Have a look at my website as well: wimsmuseum.jouwweb.nl

[@algorithminc.8850]

@@wimderkinderen1952 Wow - very nice - greatly enjoyed your website - lots of fun bits on there. Sincere thanks. All the best ...

[@windward2818]

I have tried to sum up the demo in the text below, please review and correct any errors in the description, this would help me understand. The crossbar switch as shown is a latched finger mechanical memory reserving (holding relay) pairs of phones or conversations for a maximum of 4 simultaneous conversations out of 18 extensions (2x9) with one pair (19,20) reserved for line finding and control (Tones and ringing). This would increase the equipment density in the routine of calls by about 10 to 1 as compared to a Strowger click and bang. The microcontroller is used as a basic counting decoder and tone controller, which controls the crossbar to route calls between two extensions (numbers) that it decodes (it knows how many numbers are needed to dial, and includes a timeout after a lengthy delay if the number dialed is incomplete). This is different from the Strowger which integrates simultaneously counting, routing and memory (which is ensured by its basic operating technique). In the USA, traditionally for land lines, you have an area code (three digits, know as long distance), followed by an exchange code (three digits) followed by the number within the exchange of up to 10,000 numbers (0000 to 9999) with some number sequences reserved either by starting digit or number depending on the function. So, in basic terms the challenge before us is to create separate telephone exchanges of 10,000 numbers each, such that the equipment used must be able to detect, count, route and remember (while the call is in progress) with a maximum of 5000 simultaneous conversations local to the exchange, although I link only a small percentage is really used like perhaps 10% for a maximum number of simultaneous conversations of 500? Although, this number probably expandable if the billing statistics result in too many blocked calls.

[@wimderkinderen1952]

Leave your email here and I will send a more detailed description

[@hughs591]

Thank you for this most interesting and informative video; fascinating (though I had to watch it more than once to take in all the information!)

[@wimderkinderen1952]

It took me quite a while to understand the crossbar switch. It is not as straight-forward as the Stronger selector. I hope that the introductory section with the separate relay helps to grasp the fundamentals of the crossbar switch.

[@spotterinc.engineering5207]

Wonderful project!! I managed product and installed LM Ericsson PABX's in the USA for over10 years i the 1970's. ARD-561, AKD-741, and French Ericsson CP-100. I probably installed over 100 systems. I love crossbar systems. Would like to get a crossbar switch myself and build a project like yours.

[@Vintagetelephoneexchange-fn1xn]

Hi Wim, good work! It's not easy to explain how a crossbar works since the insides are mostly hidden. I like your demo using a "paper clip" to assist in closing the relays contacts much like how the selecting finger works in a real XB switch. Your demo is clean and looks great! - Al

[@wimderkinderen1952]

Thanks for your comment. I had a quick look at your excellent videos and will have another go later. Is this your equipment or do you record the videos in a museum? Best wishes, Wim

[@ClicketyClack]

Beautiful!

[@edgeeffect]

That's a great description of how crossbar works. Previous to this, it was all just "black magic" to me... now it's all quite clear. I didn't realise crossbar switches were ever so small... but I suppose it's obvious they would be - for private switchboards.... that's perfect for tinkering with - very "hobbyist friendly"... I would love to have one. I thought we only had "ring, ring....... ring, ring...... ring, ring......." in the UK.... I thought the whole of the rest of the world was "Briiiiiiiiing.......... Briiiiiiiiing.......... Briiiiiiiing" like in North America. In my projects, I always call it "the UK ringing cadence".... I'll have to find out how widespread it actually is, and update my documentation.

[@AenesidemusOZ]

We used the same cadence here in Australia.

[@yewenyi]

I designed a crossbar relay set for Telstra back in the day when it was telecom Australia.

[@TheGmr140]

Very cool 😊😊

[@ericfrazer4736]

interesting thank you!!

[@ds99]

It’s very interesting. I grew up in a section of the city that was run by a crossbar #2 exchange. What if you had 5 phones wanting to call on that switch. How could a call to extension 18 happen if extension 17 was already engaged in a call? That part doesn’t make sense to me. Wouldn’t that disrupt the call on 17? Thanks for this demo.

[@wimderkinderen1952]

My specimen of the Xbar switch can connect to 16 phones, but only two calls can be made simultaneously. I have configured only two phone connections.

[@OLIBAHN475]

cool.. 👍

[@ladronsiman1471]

beautiful ..i lived a bit that age ,before all went digital

[@martiensmits588]

Nice work Wim, Is there a way to do this all with only arduino or esp?

[@wimderkinderen1952]

Yes, Martien, an Arduino or ESP32 in combination with some additional components (Songle relays or MOSFETs, and a ringer module) could do everything, but …. bringing the vintage stuff to life is more fun 😂

[@martiensmits588]

@@wimderkinderen1952 Thank you for your answer. I like this technology. Unfortunately I don't have the room en money to use Crossbar switches or step by step switches. Yes it wil be more fun in the original style😉

[@kippie80]

How many connections can this switch handle? Seems to depend on where the two respective lines are on the switch.

[@wimderkinderen1952]

My specimen can have four connections and therefore can handle two calls simultaneously. Each call engages two holding magnets. The connections are multipled between contact banks, so each connection can be routed through any of the four vertical relay blocks.

[@jefferyswan4401]

I have been trying to find a crossbar switch (or a few) to purchase. Do you have any suggestions? Kind regards.

[@wimderkinderen1952]

Hi Jeffery, Crossbar switches are apparently difficult to find. I got mine from the Houweling museum in Rotterdam. It was the only spare. Maybe they were more widespread in Sweden? I don’t have contacts there but there should be an Ericsson legacy society.

[@martinkuliza]

0:24 yes i know they were used in exchanges................. I HAVE ONE IN MY BEDROOM haha and yes it is as cool as it sounds and yes, it's as bloody heavy as it sounds Talk about Heavy Matel... Pick up a crossbar switch sometime....... Just 1 Now.. that's an Ab Workout EDIT 0:45 OK, I SEE I HAVE A FORMIDABLE OPPONENT and we are going to compare scars like they did in jaws LOL My one was ..... Ever so graciously donated to me by the 2 gentleman at the Decommissioned Telstra Exchange in Melbourne , which is now known as the Telstra Exchange Museum it's not open to civilians, it is however open to techs and me and a friend some years back while doing our Open Cablers Registration were told quietly by our instructor that by appointment we could visit the exchange Museum I cannot stress how cool it was Not only did we see multimeters that had NIXIE TUBES.......Ohhhh that was electronics porn and a half Not only did we see Underground Telecomms cable so thick it would make you feel indimated Not only did i see the old Mickey Mouse and Garfield Phones of the 80s Not only did i get to use an old hand cranked Phone to generate the AC for the ring I GOT TO USE THE ACTUAL PATCH PANEL, THAT THE GIRLS USED TO USE IN THE PATCHING DAYS. I successfully made a call from the panel to a phone, step by step via old Telecomm's procedure and we got to see "The Rack" we got to see the underground decommissioned tunnels where i was convinced they kept the bodies of deceased Lines men that were being preserved and genetically modified to form a new super race of Telco Lines man LOL But yeah, when these guys gave me the crossbar switch... I'm lying if i say i wasn't emotional. IT WAS SUCH A NICE GESTURE, Forever Grateful

[@activelow9297]

How many simultaneous calls can this device switch?

[@wimderkinderen1952]

Each call requires two holding magnets to remain activated. My crossbar element can have 16 extensions but only two simultaneous calls. That is why a telephone exchange has many crossbar elements.

[@tei1155]

Is it possible to call from number 4 to number 3?

[@wimderkinderen1952]

Yes, as indicated in the schematic, extensions can be multipled between contact banks. So, if 4 calls 3, the extension of 3 in the second bank will be used because 4 already locks holding magnet V0.

[@tei1155]

​@@wimderkinderen1952 Thank you! Now I understand.

[@ruudshangout]

Een prachtig YT kanaal heb je Wim, misschien vind je de mijne ook wel leuk :-)

[@wimderkinderen1952]

Jouw kanaal is ook heel interessant, Ruud. Ik heb al een paar videos bekeken. Je stopt er ook wat meer humor in dan ik! 😂

[@ruudshangout]

@@wimderkinderen1952 Bedankt, vanavond na het werk kijk ik je video's. Ziet er veelbelovend uit. 😁