The Double Current Interface

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M1ECY
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The Double Current Interface

#1

Beitrag: # 27672Beitrag M1ECY »

Hi All,

I have been building some systems here for loan to Museums in the UK, one of the problems for I-Telex in the UK is the lack of Double Current signalling as an "Off The Shelf" solution.

UK specification teleprinters are generally found with a 3 wire double current or V.21 signalling system - the Analogue Card takes care of the latter, and with a UT55A converter it is possible to run a DC machine with V.21 interface, however these modules are rare, and ones that do exist often need a lot of component level repair and refurbishment - not something that all UK enthusiasts are completely happy to do.

There have been some versions of the DC interface card designed by Fred over on the Sourceforge pages, but most were concept ideas, or prototype designs, as such not tested fully.

Henning and Fred are still working on the latest version of this interface card.

Being a little impatient, last year I worked with Jeff Angus, to come up with an external solution - this will allow UK spec machines to interface with a Single Current Control unit, and drive a DC Teleprinter - this is still in testing and development (Sorry, lots going on here!) In parallel with this innovative solution, I also had some of the I-Telex interface boards made - A very early DC board, and the later 1.50 revision.

The earlier version lacks the galvanic isolation of the later design, and will probably be tested at a very low voltage to work on a third type of UK machine, which works with a +/-6V signalling system - more to follow on this version in another thread.

Onto the Version 1.50 Card.

This is designed as a universal board - it can be built for single or double current use - being a prototype, there are some errors that have been corrected in the later design, this is a fairly minor issue, some component changes, and one addition that is easily placed into the board.

I have built a couple of these cards, and over the past few days, with a lot of help from Fred remotely have managed to get a working interface to I-Telex.

The signalling current is using a much lower loop voltage, which for short connections between I-Telex and the Teleprinter is completely acceptable - the 40V supplied by the original I-Telex Power Supply board works well in the short testing completed yesterday evening.

One of the museums that I am working with is situated in a "Nuclear Bunker" this is an underground structure over several floors, as such the previously installed telex system has many kilometres of wiring - to keep the loop current to a high enough value to drive the printer it is envisaged that the higher voltage will be needed - this will be tested once the interface card is proven completely.

So far everything looks promising - I have to discuss a small software modification with Fred, due to the way the UK Control Unit is working, hopefully this is a simple change to make, and then for the fist time since the closure of the UK Telex system there will be a viable solution to allow these machines to join in.

More work to do on this, but I thought an early report of the work so far would be good for any of our UK members to see that there is good progress, and perhaps this will allow them to begin the experience of joining the I-Telex network.

All of this would not be possible if it was not for the help and support received from Fred, and Henning - Thanks both - really appreciate what you are doing, and apologise for all the silly questions :)


Will continue to add to the thread as more progress is made,

Cheers
Sean
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M1ECY
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Re: The Double Current Interface

#2

Beitrag: # 27733Beitrag M1ECY »

Time for an update.

Once again thanks to Fred for help and support with some adjustments to the software for the interface card.

Some small changes were needed to allow the Control Unit (FSG) to perform correctly - In Telex service from the old exchanges in the UK there was a need for the exchange to return a negative pulse to the Teleprinter to indicate that the exchange was ready to accept the dialled number.

With this in place calling out is now a one handed operation, as it should be, and the system seems to perform very well.

There is one unavoidable detail when "Clearing Down" the call, which is a function of the Double Current system - when the line clears, the Teleprinter will print one random character, due to the change of state when the line drops - this is unavoidable, and isnt really much to worry about.

I hope to get the new "Development" system onto the server soon, then I can test incoming calls as well, but I expect this to work without fault due to this being something that is already half tested.

Exactly one year since getting this Creed 444 into the collection, and it is working properly again.

Looking forward to getting some two way use soon.

Cheers
Sean
669089 Siemen G - T100S Online 24H
299709 Antosh G - Creed 444 - Double Current R + D (0800 - 2100) and a bit tempremental
459724 NC
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M1ECY
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Re: The Double Current Interface

#3

Beitrag: # 35385Beitrag M1ECY »

Bit of an update....

I received a kit of parts from Henning for the Version 1.52 Universal Line Current Interface just before Christmas.

I have since assembled this kit as a twin Double Current interface - it is important to understand that these cards only work with the later power supply card.

The Creed 444 (299709 Antosh G) is now connected to this interface, and is working with TW39PLUS Firmware - the original slight issue of the dial not staying energised after dial button press is still there, but for now this is an acceptable compromise, just means I need to use two hands to dial :)

I will produce an updated drawing that shows the correct bridges to use on the universal card for D.C. use - In the case of my system here, I was able to use +-40v which means the optocouplers and switching transistors of the original design are working safely in their limits.

It's good to be able to finally use an English machine on the network.
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299709 Antosh G - Creed 444 - Double Current R + D (0800 - 2100) and a bit tempremental
459724 NC
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Re: The Double Current Interface

#4

Beitrag: # 35386Beitrag M1ECY »

At the request of Henning, a small document to help with assembly.
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Re: The Double Current Interface

#5

Beitrag: # 35395Beitrag FredSonnenrein »

Hello Sean,
M1ECY hat geschrieben: Do 29. Dez 2022, 16:57 The Creed 444 (299709 Antosh G) is now connected to this interface, and is working with TW39PLUS Firmware - the original slight issue of the dial not staying energised after dial button press is still there, but for now this is an acceptable compromise, just means I need to use two hands to dial :)
Can you tell us the reason why ypu don't use the dedicated double current firmware?

Yes, that firmware is almost identical to the TW39Plus, but only almost...

See the page https://wiki.telexforum.de/index.php?ti ... -Varianten for the available firmware variants...

And it will be easily possible to adjust the "protocol" to avoid needing two hands...

Best regards,

Fred
Grüße,
Fred Sonnenrein, Braunschweig
i-Telex 952741 (Lo133), 8579924 (T100s), 781272 (T100), 792911 (T68d) oder 531072 (T.typ.72)
Bei besetzt oder gestört bitte 531002 versuchen.
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Re: The Double Current Interface

#6

Beitrag: # 35404Beitrag M1ECY »

Hi Fred,

Sorry, I had not found the dedicated firmware - This will be something I test shortly.
669089 Siemen G - T100S Online 24H
299709 Antosh G - Creed 444 - Double Current R + D (0800 - 2100) and a bit tempremental
459724 NC
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M1ECY
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Re: The Double Current Interface

#7

Beitrag: # 35418Beitrag M1ECY »

Hello Fred,

I installed the itlx_Doppelstrom-EN firmware, but there are some bugs.

Perhaps this was the wrong FW?

Bug 1

The two handed dialling problem still exists.

Bug 2

When the remote connection ends the call the machine stays "Racing", so I guess there is no change in state to turn the machine off.

Otherwise operation is all fine.

Thanks
Sean
669089 Siemen G - T100S Online 24H
299709 Antosh G - Creed 444 - Double Current R + D (0800 - 2100) and a bit tempremental
459724 NC
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FredSonnenrein
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Re: The Double Current Interface

#8

Beitrag: # 35428Beitrag FredSonnenrein »

Hi Sean,

The second Problem may be caused by the „weak space“ current provided in idle state.

Try to reduce the resistor R215 resp. R225 to increase the idle line current.

Best regards.

Fred
Grüße,
Fred Sonnenrein, Braunschweig
i-Telex 952741 (Lo133), 8579924 (T100s), 781272 (T100), 792911 (T68d) oder 531072 (T.typ.72)
Bei besetzt oder gestört bitte 531002 versuchen.
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Topic author
M1ECY
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Re: The Double Current Interface

#9

Beitrag: # 35433Beitrag M1ECY »

Hi Fred,

I can try this of course, but the card functioned correctly under the TW39Plus FW - does this mean that the idle state is different between the two firmwares?
669089 Siemen G - T100S Online 24H
299709 Antosh G - Creed 444 - Double Current R + D (0800 - 2100) and a bit tempremental
459724 NC
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FredSonnenrein
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Re: The Double Current Interface

#10

Beitrag: # 35441Beitrag FredSonnenrein »

I need to check this.

Which versions did you have used for the tests?
Grüße,
Fred Sonnenrein, Braunschweig
i-Telex 952741 (Lo133), 8579924 (T100s), 781272 (T100), 792911 (T68d) oder 531072 (T.typ.72)
Bei besetzt oder gestört bitte 531002 versuchen.
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