Author Topic: Miniature 10-line telephone exchange using 22 relays  (Read 18164 times)

Online twocvbloke

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #15 on: August 24, 2013, 04:27:08 AM »
For a dial tone, all you really need is something that plays a tone that you can identify as being the dial tone for the system, rather than being something like what you'd hear on a current landline or on something like a Panasonic PBX, and make it something different so other people can identify it as not being a landline dial tone... :)

Though I don't think a "mains hum" dial tone as per the design of the system specifies would really sound good, it'd just sound like, well, mains hum, which makes phones sound like they're faulty... :D

Shame you couldn't incorporate something like this though:

https://www.youtube.com/watch?v=VzIXvO6RahQ

Offline GTC

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #16 on: August 24, 2013, 05:00:42 AM »
For a dial tone, all you really need is something that plays a tone that you can identify as being the dial tone for the system, rather than being something like what you'd hear on a current landline or on something like a Panasonic PBX, and make it something different so other people can identify it as not being a landline dial tone... :)

Though I don't think a "mains hum" dial tone as per the design of the system specifies would really sound good, it'd just sound like, well, mains hum, which makes phones sound like they're faulty... :D

I agree with what you say about mains hum, and I'd love to have a modulated tone a la exchanges, but I'm looking for a simple solution. I'll probably just use a simple oscillator.

However, if there's a cheap and available PBX module out there I'll use it.

Quote
Shame you couldn't incorporate something like this though:

https://www.youtube.com/watch?v=VzIXvO6RahQ

I love those old motorized tone generators.

How about this one:




Offline DavePEI

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #17 on: August 24, 2013, 06:05:22 AM »
Thanks for the tip regarding the 330 ohm resistor. I had it in mind to install a fuse in the ringer circuit. I may do both.
No need to do both. If you encounter a short, or a shorted coil on a ringer, the 330 ohm resistor will present a proper load on the device, and protect it from damage.

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Offline GTC

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #18 on: August 24, 2013, 11:17:18 AM »
Thanks for the tip regarding the 330 ohm resistor. I had it in mind to install a fuse in the ringer circuit. I may do both.
No need to do both. If you encounter a short, or a shorted coil on a ringer, the 330 ohm resistor will present a proper load on the device, and protect it from damage.

Dave

True, but a fuse gives a hard indication of a fault condition.

Offline GTC

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #19 on: August 27, 2013, 09:22:17 AM »
I mentioned earlier that I'm constructing the 1993 Maplin Ring Simulator project and that I outsourced manufacture of the PCB. Well, the board cam today and the etching is very well done (as it should be for the price charged) but there's a problem ... the guy making the board enlarged my layout image to fit the board size that I specified without referring that decision to me beforehand. I had mentioned in an earlier email that I specified a larger board to allow for mounting.

Result is the component drill holes are about 10% further apart than they should be. Not such a problem for resistors and capacitors but fatal for DIL chips.

He's apologised and undertaken to do the job again at his cost, this time using the image transfer at 1:1 as I expected the first time around.

Offline Owain

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #20 on: August 27, 2013, 04:31:16 PM »
Oh dear.

If you get some wirewrap DIL sockets you can maybe spread the legs on them to fit the enlarged board; it'll look like a spider perched on the board but might enable you to use the 'free' board for a second module.

http://www.rapidonline.com/cables-connectors/wirewrap-turned-pin-dil-sockets-truconnect-63770/

Offline GTC

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #21 on: August 27, 2013, 08:07:42 PM »
Oh dear.

If you get some wirewrap DIL sockets you can maybe spread the legs on them to fit the enlarged board; it'll look like a spider perched on the board but might enable you to use the 'free' board for a second module.

http://www.rapidonline.com/cables-connectors/wirewrap-turned-pin-dil-sockets-truconnect-63770/

Thanks, that's good idea. Hopefully the replacement will be correct, otherwise I may have to adopt the "spider" approach.

Offline Owain

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #22 on: August 28, 2013, 10:59:02 AM »
I agree with what you say about mains hum, and I'd love to have a modulated tone a la exchanges, but I'm looking for a simple solution. I'll probably just use a simple oscillator.

Audio store/replay chips/modules are so cheap now, especially as you only need a second of tone and can loop it, that you could easily capture some dialling tone from somewhere.

For a rather comprehensive recording of British telephone tones, listen to
https://www.youtube.com/watch?v=rYa9DPgWSk8

At about 7' there is interrupted 50Hz AC as a ringing tone on a small railway PAX
« Last Edit: August 28, 2013, 11:03:19 AM by Owain »

Online twocvbloke

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #23 on: August 28, 2013, 11:08:21 AM »
I like the doorbell dial tone... :D

Offline GTC

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #24 on: August 29, 2013, 02:13:06 AM »
Audio store/replay chips/modules are so cheap now, especially as you only need a second of tone and can loop it, that you could easily capture some dialling tone from somewhere.

For a rather comprehensive recording of British telephone tones, listen to
https://www.youtube.com/watch?v=rYa9DPgWSk8

At about 7' there is interrupted 50Hz AC as a ringing tone on a small railway PAX

Thanks again. That's quite a comprehensive sound clip.

Those are all good ideas, but I have just bought this:

http://tinyurl.com/qxegc8s


Offline Owain

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #25 on: August 29, 2013, 03:21:32 AM »
I think it would be nice to built the relay PBX actually as designed; it's kinda vintage in its own way.

Offline GTC

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #26 on: August 29, 2013, 03:26:10 AM »
I like the doorbell dial tone... :D

That's bizarre! It made me think of a potential alternative: a cuckoo clock chiming. That would've been a very applicable tone for a couple of companies that I've worked in.  LOL!!!

Offline GTC

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #27 on: August 29, 2013, 03:42:10 AM »
I think it would be nice to built the relay PBX actually as designed; it's kinda vintage in its own way.

True, but as I had to replace the power supply owing to the unavailability of a suitable transformer for the original design at anything like a reasonable cost, I needed a new dial tone option. There was no way I'd tap off the 240 volt mains to use 50Hz hum, and the idea of using a (say) 240 to 12.6 volt transformer simply to get (uninterrupted) low voltage hum wasn't very attractive to me either.

Looking at that tone generator chip prompted me to notice that this design apparently doesn't cater for busy tone. If not, then I'll try to figure out how to do that now that I have a suitable generator on hand.

When I get the time, I should combine the schematic into one diagram so that I can trace out the various signal and control paths more easily than I can over two pages. If I can digitize it then it will also enable production of a wiring diagram.

I realize that I'm wandering a bit from the vintage electromechanical design but, with 22 relays in it, it's still vintage and electromechanical enough for me.

Offline rdelius

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #28 on: August 29, 2013, 11:45:13 AM »
I made a dial tone generator with a small brush type dc motor in series with a filtered power supply feeding a small transformer on the low impeadance side

Offline dsk

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Re: Miniature 10-line telephone exchange using 22 relays
« Reply #29 on: August 29, 2013, 12:00:04 PM »
My PAX dial tone and ringing here:
http://www.classicrotaryphones.com/forum/index.php?action=dlattach;topic=4185.0;attach=34107

One vibrator making the dial tone (and busy), another the 25Hz ringing. 

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