Single line phones with KSU - Loop Detectors

[erco]

I often get asked about how to attach single line phones to the KSU.

These are called "loop detectors" and used to be very common products from Melco (S64-1) and Sandman used to sell them too.

These days it looks like Viking still sells these as the Viking LDB-1:

I've not tried the LDB-1 myself, but looks like it might work. Especially since these use their own 12V supply, similar to what the Seriss KSU uses (instead of 24VDC more common to the old AT&T KSUs).

I'll try to investigate these devices and follow up with connection suggestions.

Seem to be around $40 ~ $50 currently (July 2024) for new ones, depending on the supplier.

[Greg Ercolano]

On 8/29/24 00:44, Luky Kuky wrote:

Hello,I also want to say that the vyking LDB-1 does not use a 12 power supply. The relay is powered from the telephone line.  12 volts is only for powering the output. By connecting 12 V, 12 V will be given to the output of the relay.

Hi Lukas,

    Thanks for the info about the LDB-1's power supply being optional for its function as a loop detector, and the line powered relay circuit, which works IF you can find a relay sensitive enough to trigger properly. There are special reed relays that are made for this purpose of line sense/loop detect, but I don't think they're still manufactured; info below. (It's possible "regular" reed relays may also work if spec'ed properly).

    I've purchased both an LDB-1 and LDB-2 for testing.

    The LDB-1 "works" in that picking up the single-line phone hanging off the LDB-1 triggers the A lead, lighting the 1A2 line lamps while it's off hook, and one can either answer or make calls.

    And indeed, it works fine with or without the optional Viking external 12V power supply, as it can operate powered by the CO line current, so thanks for that info, Lukas!

    The LDB-1 has a few mild issues though with respect to using it for a single-line loop detect with a 1A2 system:

        o The LDB-1 won't retrieve calls from Hold (the LDB-2 doesn't have this problem)
        o The LDB-1's relay triggers during rotary dialing (the LDB-2 doesn't have this problem)
        o The LDB-1's relay triggers during ringing (both LDB-1 and LDB-2 do this)

    More details on those below.
 
    The LDB-1 doesn't seem to allow the single-line phone to retrieve a call from Hold on the 1A2 system. Not a show stopper, but a very useful functionality is lost without that ability that the LDB-2 provides. This result was found with both the Seriss KSU (REV J6A) and Western Electric 551A KSU with 400 type line cards. From what I can tell:

Apparently when a 1A2 system has a call on Hold, the Hold resistor across the line prevents the LDB-1's line sense relay from operating, leaving the A lead open, and the line remains on Hold, and the volume of the call is muted. Hanging up the single-line phone leaves the call on Hold, until someone hangs up the line, or until the other end hangs up, hopefully causing the CO to briefly interrupt the line with a CPC, or Calling Party Control signal (aka "Disconnect Supervision") which will free the line out of Hold automatically, assuming that feature is provided by the CO equipment.

Viking's other product, the LDB-2, has a more sensitive optocoupler circuit (needs 12V to operate) which properly retrieves calls on Hold when the single-line phone goes off-hook. so one can properly pick up a 1A2 call on Hold, and hanging up is also handled properly.

The LDB-2 would be great if not for the fact it ALSO operates during ringing, apparently not an optional feature of that device. AFAIK there's no way to disable this; the manufacturer's recommendation to cut a lead on one of the LDB-2's optocouplers to disable ring detect does not seem to affect it. The manufacturer does recommend trying an LDB-3, which has a way to disable ring detect - I haven't evaluated that device yet, but plan to.

    Another smaller issue with the LDB-1 is that the relay flutters during rotary dialing of the single-line phone, causing the Line lamp on the 1A2 phones to also flutter during dialing. This is more of a cosmetic issue it seems; dialing works fine, allowing calls to be made successfully. The LDB-2 doesn't have this issue, as it has a timing circuit that keeps the relay triggered when the loop current briefly flutters.

    Both the LDB-1 and LBD-2 triggers during ringing, causing the A lead to flutter on/off at ~25Hz during each ring burst from the CO. I find this troubling, as it causes confusion for the Seriss KSU into thinking the line is in partial retrieval whenever the A lead closes. I can probably solve that with a firmware modification, but it's bad IMHO that the physical relay on the LDB-1 should have to operate on-and-off so quickly during ringing. The LDB-2 triggers once and stays on for the duration of the ring burst, so it doesn't oscillate during the 25 Hz the way the LDB-1 does.

The LDB-1's Line Powered Relay

    Regarding the LDB-1's line-powered relay: the LDB-1 I have use a TELTONE M949-01 "Line Sense" dual-coil relay (data sheet). This relay is manufactured specifically for the purpose of telecom line sensing/loop detect. It's also apparently intended for use in rotary pulse detection, though I'd offer for that purpose, optocouplers are better suited.

    From what I can tell, the TelTone relays are no longer manufactured. A different company, IXYS/Clare, has an equivalent part which both Mouser and Digikey show in their database as being obsolete and out of stock, and the manufacturer released an End Of Life (EOL) notice in 2020 indicating they're no longer being manufactured or sold after March 2021.

    That all said, the TelTone relays can still be found on ebay; I see someone selling 10 pcs for $28, which sounds pretty good; about $3 per relay:

    Note that these work by being in series with the telephone line, and will trigger during ringing and dialing unless external components are included, such as the parallel capacitors across the windings to pass AC ringing, as you show in your schematic..

..I am a bit curious to try that; might have to grab a few of those TelTone relays from ebay to do some experiments..! Western Electric had their own custom dual coil reed relay they used on the 400 type line for the line sense "L" relay, which looked like this:

..and can be found on most all of the 400 type line cards that WE provided, AFAIK.

[Luky Kuky]

Hello . You can also make the Loop Detector at home not even for  $10 . You need  relay, capacitor, and phone 😁(one-coil relay is ok, but two-coil relay is better if you have a longer cable so that the loop is not broken ). I am also attaching a wiring diagram. 

Goodbye and have a nice day 

Lukas

Dňa po 29. 7. 2024, 16:50 erco <ercola...@gmail.com> napísal(a):

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[Luky Kuky]

Hello,I also want to say that the vyking LDB-1 does not use a 12 power supply. The relay is powered from the telephone line.  12 volts is only for powering the output. By connecting 12 V, 12 V will be given to the output of the relay.

Goodbye 

Lukas

Dňa št 29. 8. 2024, 9:35 Luky Kuky <lukyk...@gmail.com> napísal(a):

[Luky Kuky]

Hello, I tried it and if you use a normal 12 volt relay it's ok. And when it rings, it doesn't respond because the relay is not on AC voltage . And when you dial using DTMF, the relay stays on, but if you dial with pulses and the relay pulses, you need to put a capacitor that has more F(you know what I mean)

Dňa št 29. 8. 2024, 20:59 Greg Ercolano <er...@seriss.com> napísal(a):

[Greg Ercolano]

On 8/29/24 12:08, Luky Kuky wrote:

Hello, I tried it and if you use a normal 12 volt relay it's ok.

    Yes, with the LDB-1 it works if 12V is applied or not.

And when it rings, it doesn't respond because the relay is not on AC voltage.

    Hmm, in my tests with the LDB-1 (I assume you're talking about that, and not your custom circuit with the parallel capacitors across the coils), the LDB-1 relay triggers on and off very quickly during ring bursts, and follows the 25Hz AC ringing.

    For my test, I put an LED and battery to the output of the LDB-1 relay, and the LED flickers at a fast rate during each ring burst from the CO. When connected to the A lead of a 1A2 system, it turns the A lead on-and-off at that same rate.

    I expect the coil of the line sense relay is in series with the T/R pair from the CO, between the CO and single-line set, and is therefore exposed to raw 105 VAC ring voltage supplied by the CO across T/R during ringing.

    I can include a small video showing the effect with the LDB-1 if need be; I just retested it a few minutes ago with a WE 500 single-line rotary set, and a WE 551 KSU.

    Since the LDB-1 doesn't include capacitors in parallel with the relay coils to pass ringing around it (like your custom circuit shows, if I understand their purpose correctly), the coil apparently operates during each cycle of the 25Hz ring voltage burst from the CO.

And when you dial using DTMF, the relay stays on, but if you dial with pulses and the relay pulses, you need to put a capacitor that has more F(you know what I mean)

    Right, I assume you mean by "F" you're referring to the farads rating of the capacitor, or in the case of most capacitors, micro-farads, usually abbreviated "uF" or "μF".

[Luky Kuky]

I'm talking about mine, not the ldb-1

Dňa št 29. 8. 2024, 21:32 Greg Ercolano <er...@seriss.com> napísal(a):

[Greg Ercolano]

On 8/29/24 12:41, Luky Kuky wrote:

I'm talking about mine, not the ldb-1

    Ah, OK.

    Can you say which relay (model#) you used for your circuit? I'm assuming a reed relay of some type.

    I ordered a few of those TelTone M949-01 relays from ebay to do some experiments with, as I don't want to mess up my LDB-1. Might look into the IXYS M-949-11 relays as well, just to see if they're better suited to handle call-on-Hold retrieval.

    If I were to do my own circuit, I'd definitely want to support Hold call retrieval, which probably means an optocoupler circuit instead of a relay. Comparing datasheets for the IXYS and TelTone relays, the IXYS is only a little more sensitive (15mA vs 18mA for the min pickup current respectively), a difference so small it probably won't matter in practice for the Hold issue.

    I do want to try out the LDB-3 though; the guys at Viking recommended it to prevent ring detection. And if it also supports retrieving calls on Hold the way the LDB-2 does, that sounds like the best situation for this application of adding single-line phones to 1A2 KSU systems. Will follow up on that when I get an LDB-3 to do some tests.

[Luky Kuky]

Hello, I can't find it exactly but this is the closest I had but in black color

Dňa št 29. 8. 2024, 22:27 Greg Ercolano <er...@seriss.com> napísal(a):

[Greg Ercolano]

So after evaluating the loop detector devices, I think the better way to attach a single line phone to a 1A2 system is with these Motorola units:  https://www.ebay.com/itm/330382384390

I tried one, and it's a great solution.

This plugs into the KSU and has a regular RJ-14 male ended 4 conductor cable that can plug into a regular single line phone, and lets it become just like a 2564 or 2565:

    * You can put calls on Hold
    * Answer calls out of Hold
    * It has a built-in for the Seriss KSU intercom
    * The buzzer responds to "BUZZ RING" programming on the KSU
    * There are normal 51a incandescent lamps under the line buttons
    * The line buttons are of high quality
    * Labels can be inserted under the buttons by popping off the clear plastic button
    * The amphenol and cable are of high quality
    * The 25pr cable is supple, not stiff (stranded wire, not solid core)
    * The single line phone's bell will ring off the selected line's CO ringing
    * There is a built-in piezo electronic ringer that responds to KSU ringing on the Y-S pair (*)

This device works great with the Seriss KSU and is just "plug and go", nothing to configure.

It is very similar to the Western Electric 6040/6041/6051 devices, e.g.

.. that pic excerpted from BSP 512-210-103.

(*) The only thing I had trouble getting working is the piezo electronic ringer inside the device; normally it would ring off the Y-S pair, but it doesn't respond to the AC half-wave diode ringing the way 1A2 phones do. I noticed if you short across the KSU's bell diodes, which effectively bypasses the diodes letting the full AC wave for ringing through the KSU, then the device's electronic ringer rings properly off the Y-S pair. The only problem with that workaround is it defeats the ability to program which lines ring using the "BELL CALL" switches on the KSU.

[Greg Ercolano]

On 9/21/24 23:54, Greg Ercolano wrote:

So after evaluating the loop detector devices, I think the better way to attach a single line phone to a 1A2 system is with these Motorola units:  https://www.ebay.com/itm/330382384390

So apparently the built in piezo ringer in these units won't ring on the Y-S if your KSU uses a diode matrix to program ringing (the standard 1A2 way to program which lines ring which extensions).

It seems no matter which way you polarize the Y-S pair, the unit's piezo ringer doesn't react to half-wave ringing. It only reacts to full wave ringing, which means diodes can't be used.

I've not searched for a practice for this device yet, so I'm not sure if there's some trick one can do to change this other than to bypass diode ringing for this extension at the KSU or diode matrix block. On the Seriss KSU this can be done by jumpering across the "BELL CALL" diodes for that extension.

So that'd be my only beef with this device; not supporting diode matrix ringing. Someone in the Motorola engineering dept dropped the ball on that one..!

[Greg Ercolano]

On 9/21/24 23:54, Greg Ercolano wrote:

So after evaluating the loop detector devices, I think the better way to attach a single line phone to a 1A2 system is with these Motorola units:  https://www.ebay.com/itm/330382384390

Regarding the line buttons, one can easily remove the clear plastic button covers by popping it off with your fingers, and inserting the label and relpacing the cover.

In the unlikely event you need to change a burned out 51a bulb, you have to disassemble the unit. Each bulb has a white diffusion cover that's under the clear plastic button cover which is retained by a plastic bezel that can only be removed by disassembly.

To change the bulbs, take the unit apart:

• Remove the 4 rubber feet (by prying them up to break the rubbery glue)
  
  
• Remove the 4 philips screws beneath the rubber feet; they are deep down a narrow plastic channel, and take /many/ turns to remove; the threading pitch is tiny!
  
  
• Bend the shells apart.
  If you're lucky , there'll be enough play in the cabling that you won't have to cut the two cable strain relief zip ties and later replace.
  
  
• Remove the other 4 screws on the back of the line button assembly that hold it in place to the plastic shell, as shown in the disassembly photo below.
  
  

At this point the line button assembly and its plastic bezel can be removed, at which point it's easy to remove the clear button cover and diffusion cover to gain access to the bulbs by popping the covers off with your fingers.

To actually remove the bulb, "the usual" clever bulb removal techniques must be used, as the bulbs are buried deep down inside the buttons. Chances are needle nose pliers  won't work. I've had good luck removing bulbs by taking a few inches of sheathing from a cat5 network cable, and twisting it down over the bulb, and then popping it out that way. YMMV.

[erco]

Hi Paul,

(Seems there was a problem getting your message into gmail, so I'm copy/pasting it here)

You wrote that when you tried the Motorola device connected to a 500 single line set, it immediately placed both lines on Hold.

Hmm, a Hold condition for a line will be triggered on the KSU if the voice path for T/R are using current (normally in an on-hook condition
this would not be the case) but the A lead is open.

> I tried tracing the Amphenol Common pin 2 and pin 27 but that didn't tone out at all.

Right, pins 2 and 27 are the A lead ground and A lead for Line 1 respectively, so if they're open but Tip/Ring are conducting, then a Hold condition will be triggered.

What you'll want to check is if pins 1 and 26 are conducting: when on-hook, they should be open (not conducting).

To test, disconnect the motorola from the KSU, and on the motorola's amphenol test for conductivity across pins 1 and 26 while on-hook vs. off-hook. It should be a completely open circuit in the on-hook condition. If not, that's the problem to solve.

Ditto for Line 2.

If it's conducting even on-hook, try unplugging the 500 set and re-test. If it's still conducting across T/R at all on the motorola amphenol even with the 500 disconnected, there might be a problem inside the motorola unit.

> Subject:

Re: [seriss-1a2-ksu] Single line phones with KSU - the better solution

> From:

Paul Ash

> Date:

10/15/24, 07:26

> To:

seriss-1a2-ksu
>

> I was excited to obtain one of these devices from eBay in the US, however, when it arrived and I connected it to a standard 500 and plugged it in to the KSU it reacted by placing the line on hold and does this for both lines (6.12 – Line goes into Hold on pickup). I can still hear dial tone but can't break dial tone to make a call, I can answer an incoming call but the line doesn't stop ringing on other phones. I wondered if anyone else had experienced this or could explain what I should do, I tried tracing the Amphenol Common pin 2 and pin 27 but that didn't tone out at all. (3 and 28 do!)  The Amphenol plug does look clean. I am working through the other suggested resolutions. Many thanks in advance for any thoughts/responses/suggestions you may have.