Doug's SxS Switch   
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Current Step Switch Progress

Updated 14 June 2009

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10 January 2009 -- Well, here it is nearly a year later with no updates or progress to report on the big switch.  However, a new project has finally started: construction of a small, portable step switch!  The plan is to have it fully operational in time for a debut at the June 2009 Lancaster, PA Telephone Exhibit hosted by Telephone Collectors International.  There the switch will be on display and operational.  Information about the show itself is on this page:

The plan for the switch is for it to have two talking paths, ten stations, with provisions for interfacing it with the step switch at home when it is not on the road, as well as other switching exhibits at the Lancaster or future shows.  Also, the switches and their associated contact banks will be fully connectorized to facilitate removal of the switches from the frame to make moving everything easier.  Step switches are very heavy and the four switches alone that will be on this frame will add around 70 pounds to the total weight.  The power supplies will also be separate from the frame.

Construction began last weekend.  I built a small wood frame (pictured at right) on which the equipment will mount.  The frame is approximately 24 inches wide by 32 inches tall, and is intended to sit on a table, though it could stand on a floor.  I have spent the week painting the frame a gray equipment-like color to make it look like a steel-framed rack, though it is really 2x4s.

The main equipment rack in the switch will be the small shelf section that I got with the equipment I got from a web page visitor, and pictured back on 5 May 2007.  I will be using the selector and connector that came with it, along with another selector and connector that I already have.  Today I worked on stripping off the old wiring on the shelf section, changed out two of the shelf jacks from 16-pin to 24-pin to accommodate the connectors, and have started wiring the battery and ground connections to the shelf jacks.  Earlier in the week I placed some parts orders for relays, capacitors, and other assorted electrical and electronic items needed to build all the "glue" stuff to make the switch function.  The switch will be a smaller version of the "big" switch I built, namely it will have a microcontroller interrupter, a solid state recorder chip playing the dial, busy and reorder tones, and will be a mix of original SxS and modern electronics.  Also, to keep the size and weight down, I will not be using conventional two-motion line finders, I have developed a circuit for an all-relay line finder that will take up considerbly less space.  There will be only ten stations on this switch so the "finder" can be appropriately smaller.

The switch will have two different connectors on it, a single line connector and a party line connector, mostly because that is what I have on hand!  To keep the dial plan simple I will wire the party line connector as a single line for now.  I had thought I would make a small switch with the party line connectors I have, but the two that I do have are completely different in operation from each other and would be a bear to set up in a small switch, plus the fact that I have little documentation for the one.

I will post photos as the project progresses.

14 January -- Mounted the shelf section on the switch frame today and hung a couple of switches on it for grins and took a photo.  There's a long way to go yet, and nothing is yet operational, but we can get an idea of what the switch will look like.  The area under the switches will hold the control circuitry like the line and cutoff relays, line finder circuits and possibly a trunk plate for connecting to other systems.

The parts orders have come in over the past couple of days so I now need to get started building some circuits! For once it looks like everything that I ordered has arrived in the shipments, nothing appears to be backordered... so I really have no excuses to not warm up the soldering iron.

What I think I will do, though, is put battery and ground to my connections on the shelf and verify that the wiring is OK so far.  The selectors I am planning to use, and are on the shelf in the photo, are interesting, at least I think so.  The one is a common 30200 selector that I was using originally on my "big switch," was manufactured in 1942, and also has a tag on it saying that it came from a ripout of the original SxS switch in Silver Creek, NY.  The other selector I recently acquired and is a multi-function selector of some kind, having four off-normal post springs.  It's a Western Electic 95858, and am told it came out of Easton, PA.

There's a lot of work yet to do on the switch, so I should really get off the computer and get to work!

17 January -- Been spending a few moments here and there over the last few days with the portable switch construction.  I have now wired in the power connections to the shelf jack wiring I have done so far and have tested the switches that are so far hung on the frame.  The connector needed some remedial work on a couple of relay leaves.  It worked fine stand-alone with only a butt set connected to its input, but when tied in to a selector, it would strangely try to reset on the first digit dialed into it after being seized.  Turns out there was a relay leaf out of adjustment in the "B" relay, which just so happened to be the leaf that grounds the sleeve lead back to the previous switch, and the vibration from the switch operating would make it not contact correctly.  Also, some slight mechanical adjustments were needed on the connector.

I also tried out the 30200 selector that came with the connector on the shelf section and needed a couple of adjustments as well, but is now working the way it should.  I have that selector tied to the connector and can dial three digits to get to a station on the connector.  Nothing, of course, yet rings since there are no L/CO relays hooked up yet or a ringing plant connected, but it sure is progress.

Had my first setback in the project today.  I went to the basement and pulled out the 10-party connector that I was planning to use as the second connector on this switch, wired as a single line connector.  I discovered that this connector is a full two inches taller than the single line connector, the height of which I used for planning the overall size of the switch frame and placement of the shelf section.  I can move the shelf, of course, but I think if I did it may not leave me enough room on the bottom part of the frame for the L/CO and trunk plate, as well as the line finder boards and other control circuitry.  I am going to have to make some precise measurements and see how I can proceed.  It might be easier to just try to come up with another 31737 or 31739 connector.  Anyone have one for sale?

19 January -- Did some work getting the 31737 connector working properly.  It has been stepping correctly and holds the previous switches' sleeve lead, but I hadn't yet tried to have the switch cut through to a dialed station.  I wired the jumpers on the shelf jack for the connector to configure the ringing polarity and attached a phone to a station pair on the connector's contact bank and a resistor on the sleeve lead to battery and dialed.  The dialed station would not ring through.  Got looking at the switch and poking around at things and found that the "K" relay was not pulling in fully, only part way.  Foruntately I had received the switch and shelf with some documentation so I dug that out and started reading up on the 31737 connector.  I discovered that the "K" relay was only partly operating and tracing the schematic I found that the operation of the "B" relay was supposed to fully operate the "K" relay.  The relay contact in question on the "B" relay was out of adjustment, preventing the "K" relay operating fully.

I got that adjusted and the "K" relay now operated as it should, but the dialed station still would not ring.  Watching the switch operate, as soon as the dialed station was reached and the line relay operated, the "F" relay also operated.  That's not correct.  The "F" relay shouldn't operate until the called station goes off hook.  Turns out the previous owner of this switch had wired in a slight circuit change to make the "F" relay operate right away so the called station could go off hook and talk without any ringing power being applied.  The little demo switch that was originally configured on this shelf section didn't appear to have any ringing input, only battery and ground.  I looked at the schematic and traced out where this tacked-in extra circuitry went and it was indeed set up to operate the "F" relay without having trip battery or ringing power applied.  I removed that extra wiring and now the switch operates per spec.  Dial the station desired and ringing is applied until the station answers.  Yesterday I put out a call on the TCI email list for another 31737 (or 31739) connector, but so far no bites.  I may end up rearranging the shelf on the frame to use that party line connector yet.

24 January -- Built up the "ringing machine" for the switch yesterday.  It is based on a Black Magic chip and provides superimposed ringing power so there is full trip supervision.  I got the circuit to do that from another switcher a while back and it works great.  Today I hooked up the ringing generator to the switch and did some testing.  I discovered in the process that there was yet another relay leaf "out of whack" in the 31737 connector's "B" relay because the Motor Start lead did not work at first.  With some judicious leaf bending I got that working again.

The ringing board has been interfaced with the microcontroller interrupter board that will be used with this switch.  This microcontroller board is using the same firmware as I am using on the big switch.  The plan is to have a digital playback chip providing the old-style dial tone, busy and reorder tones on the small switch.  I still have to build up the digital playboard board.

I had hoped to start building the all-relay line finders this weekend but found that I was sent the wrong voltage capacitors.  I had ordered 35 of the 50-volt caps... they sent me 35 of the 35-volt ones.  Arrgh.  I also put out another call for a 31737 connector on the phone collecting email list.  I was given a name as a lead to follow up on.

1 February -- Been busy this weekend working on the portable switch.  Yesterday I wired up a line finder board and got it tacked into the switch for testing.  I found that I have another setback in the project; discovered that the line finder circuit will not "play nice" with a second finder board.  Stations going off hook after one station has been seized on the board will also be seized, dropping the next station(s) into the existing conversation.  Not good.  I am looking at how full control can be passed from one board to the next but unfortunately it's not as simple as passing the start lead on to the next board; I am already doing that and that's when I discovered the problem.  I am currently studying my schematic and seeing how I can manage to have two of these all-relay LFs coexist with each other so that I can have a two talking path switch.  I don't have the luxury of the original SxS engineers having things like many multiple pole relays at their disposal, I have only 4PDT relays!

I took a photo of the switch in its current state (at right)... what a mess.  The L/CO box is on the bottom at the right, the LF board is to the left of that.  Almost everything is tacked in or hand spliced or whatever at the moment.  I need to start building the framework on the bottom portion of the overall frame on which to mount the L/CO plate and the trunk plate, as well as mounting the other circuitry like the ringing and interrupter board and eventually the LF boards, once I figure out how to get those going properly.

For testing purposes, I do have the switch functioning with three-digit dialing.  One selector is tied to the connector so I can dial "for real" in testing the line finder board, making sure the connection doesn't drop out at some point in the call progress.  The search for a second connector continues.  Last weekend it looked like I had a lead on one, but that fell through early in the week so I have a request in with another switcher who is going to look to see what he has to spare and will get back to me.  With the line finder problem I could be building this thing with one path anyway!

7 February -- Redesigned the line finder circuit earlier in the week and built it up on a smaller experimental board before totally rewiring the board I built last week to make sure it actually works.   I finally got to hook it up to the L/CO plate and selector this afternoon and ... it works!  It looks like I finally have a workable circuit for an all-relay line finder that will find only one station at a time.  The previous version of the circuit I was using would allow other stations going off-hook to drop into a call in progress.  Now I need to completely rewire the finder board.  It shouldn't be too bad, but I do need to strip all of the wiring off and start from scratch since the circuit is very different.

Also, regular visitors will notice that I worked on the web site.  I moved the entries from January 2005 through January 2008 off to their own page since that is getting to be old news, and now the current page has only the most recent entries.  It should make it a little more user friendly for reading.

Now I need to get to that finder board... and start building the second finder board.

15 February -- The redesigned line finder circuit gave some problems with the capacitors that I had bought to use with it.  The voltage rating was too low for them to function properly in the circuit (they were rated at 50V for use in a 48V circuit, but it was all I could get at the one vendor), so I ended up having to get some higher rated ones.  Those, fortunately, appear to work great.  I think the LF circuit is finally ready.  I now need to build a second LF board for the second talk path in the switch, though I still don't have a connector switch for that second path.  A contact had said he would look to see if he had any connectors to spare and I haven't heard back yet from him.

With the LF circuit finalized, other work can continue on the switch.  Yesterday I added "fly leads" to the L/CO plate and added some aluminum bars to the switch frame on which I will build mounting rails for the L/CO plate and the trunk plate.  The "serious" wiring of the switch can then begin.  I believe I have worked out where/how I will manage the various station and internal connections.  I still need to work on getting the contact banks for the various switches wired up and connectorized.  That will be a big job, I think.

However, things are progressing.  This is turning out to be a fun project.

16 February -- Spent some time doing mechanical work on the switch frame.  The mounting rails were drilled and installed for the L/CO plate and the trunk plate.  The switch as it appears at the moment is pictured at left.  Nothing is yet wired up, and the shelf jack for the trunk plate still needs to be installed.  However, it is definitely progress.  The L/CO plate also needs a mounting bolt drilled and installed to hold the plate on the frame.  That will not be removed when the switch is moved and will be wired in permanently, so the bolt will be needed to keep it from sliding off in transit.

The next mechanical puzzle will be to figure out how the line finder boards will be mounted in the area to the left of the trunk and L/CO plates.  I am leaning toward having the two LF boards stacked and mounted as one unit.  I haven't had a chance to sit down and really look at the one LF board and think about the best way for mounting it securely.  The interrupter and ringing board will be mounted to the left of the trunk and L/CO.  There will also be a board with the old dial/busy tone recording that will be interwired with the interrupter.  What looked like a lot of space in the lower part of the switch is quickly disappearing!

22 February -- Been puttering with the portable switch over the last few days and now have the shelf jack mounted and installed for the trunk plate (picture at left).  With that completed the L/CO plate could be permanently mounted so that was bolted into place and a punch down block was installed and the fly leads from the L/CO that I installed last week were terminated on the terminal block.  The connector banks and line finder boards will all terminate here to help with the wire management of the switch.  Another punch down block is planned for the other side of the back of the switch to manage the selector connections.

With the trunk plate now on a connector, I did a little testing of the unit since I have not had power to it before.  I have documentation for it so was able to put the right inputs in the right places and have it work.  There are two trunk circuits on the plate and both appear to be working fine.

In other work, today I got the ringing and interrupter board closer to completion by mounting a 12V regulator on that board.  I have a nice nominal 12V power supply, but the Black Magic ringing supply on the board wants to see between 11 and 14 volts, but this supply puts out over 16 no load.  So I put in the regulator to keep from frying the Black Magic chip.

1 March -- Spent the weekend finishing up the first line finder board and building the second one.  They are pictured at left.  Now I need to mount them on the switch frame.  I think I have worked out how I will do it and will utilize another punch down block in the back of the frame to help manage the wiring.  Step switches are rather simple affairs, but the intra-switch wiring can be a real bear!  Lots and lots of leads to keep track of, even in a small 10-station switch like this is going to be.

I need to make a trip to the hardware store for a few sundries to help with the mounting of the boards on the frame, but the project is moving along.  Someone on one of the phone club email lists noted this weekend that it is 15 weeks until the Lancaster, PA show... so I gotta keep at it!

14 March -- Well, the last few months' worth of work on the all-relay finder board has been completely for naught.

Last weekend I mounted some alumnium strap on the frame, got it all drilled and ready to mount the line finder boards and I started wiring them in to the switch.  Then the fun began.  The circuit is unreliable and touchy at best.  It worked great on the breadboard for one or two lines' worth, but not as two entire boards.  The fault appears to be with the relays themselves.  It looks like I am operating them too close to their operate/non-operate margins so that the relays operate OK for some line circuits, but others don't work at all.  Some relays were half-operating creating all sorts of havoc between the two boards so that neither board would "find" the off-hook station, and even with only one board connected, some line circuits just don't operate properly.  To say that I am disappointed, mad, etc. would be an understatement since I had planned the entire switch around this extremely vital circuit that was operating perfectly in the development phase.  I have had no end of trouble with this blasted circuit since the beginning, what with the problems I had obtaining the capacitors I needed for the circuit and on from there.

I have a rotary relay uniselector around which I could build a line finder, I guess, but that means starting over in the design phase and when I have only the weekends to work on this and time is running out quickly, I am about to toss the entire project on the scrap heap.

Since I have still been unable to find another connector switch for this project (a contact has not gotten back to me despite a reminder email), I guess I will dig out a regular two-motion line finder and build up a very simple and boring one-path switch with a LF, SEL and CONN.  It would have been nice to have two paths, and perhaps I can in the future, but this thing needs to be ready to roll in about two months.

Disgusted and discouraged?  You bet.

15 March -- I have calmed down since the discovery yesterday that the all-relay line finders are not going to work.  I went to the cellar and dug out a line finder, one of the Northern Electric finders that I got from a web site visitor a few years ago (2004!!) -- thanks again, Neil, if you still read this -- and put it on the frame.  I don't have a contact bank attached to the finder yet but I just did some preliminary tests and when the start lead is grounded it steps up and with careful placement of a clip lead while it is stepping up the shaft stops and then hunts horizontally as it should.  Now I need to start some intensive contact bank work.  I have one finder bank that is in so-so condition.  The lower levels are OK so that should be OK, but the bank is missing the lower mounting bracket for the level commutator so I will need to engineer something to hold that in place properly.  I will also need to tap into the various line and sleeve conact leads on the bank, which is hacked off from something else, as most of us switchers get into with reusing contact banks.

I also need to work on the selector and connector banks and get those wired up.  The plan for the switch now is to be a one-path four-digit switch, with a LF, two SELs and a CONN.  I have to change some of the wiring on the shelf connectors since I was planning for two SELs and two CONNs to be mounted on same, and I can't put the LF on the currently open switch position on the extreme right because the bigger contact bank for the finder will not clear the L/CO plate just below that position.  Oh well, always something.

I am still smoldering about the outcome of those relay finders, though...

22 March -- The project is moving along well.  Spent the week working with the contact bank for the NE line finder and got a level wired up to a DB37 connector, and made up a cable with a matching connector to wire into the switch frame.  I made some preliminary tests Friday evening and the finder wasn't working quite to spec, so it was time to dig out the docs and study up on the line finder's operation.  As usual, it was a dirty contact in the "B" relay, combined with wipers that weren't quite in exact alignment.  By Saturday afternoon the finder was connected to the L/CO and each line would be properly found when going off hook.

Then it was on to a selector bank.  A bank was wired with an outlet on each level so that the configuration of the switch can be easily changed for wharever application or demo it is involved in.  Again, DB37s were wired to the bank and to a cable and connected to the switch frame and tested.  The photo at left shows a close-up of the finder (extreme right) and first selector from behind, showing the DB37s.  When the switch is transported, the bank connectors will be pulled and the switches removed from the frame and transported separately to reduce the overall weight.  Next to be done are to put connectors on the contact banks for the second selector and the connector/final selector.

6 April -- Today calls were completed through the switch for the first time!  Over the last two weekends I have wired up the contact banks on the second selector and connector switches and wired their mating connectors into the switch frame.  As of today calls can be completed between ten stations on the switch.  There are no progress tones at the moment and no ringing wired in permanently.  For now, battery is connected to the ringing inputs on the connector switch so called stations can answer and trip the "ringing" which doesn't exist.  Next up is to finish up the interrupter/ringing "machine" board and wire that into the switch.  I also need to build up one of my ISD playback chip dial/busy tone source boards.

However, it is significant progress to now be able to dial complete calls on the switch.  In addition to the ten regular stations on the switch, I also added connections for two outgoing only stations, that is, stations to which calls can be dialed, but they cannot initiate calls because they are not connected to any L/CO relays.  I am thinking to shows where the Audichron machine makes an appearance and that would be a perfect application for the call-only lines from this switch.  The Audichron would not be making any outbound calls, only accepting calls.

There is still work to be done.  The ringing machine and tone sources need to be finished, and the trunk plate needs to be wired in, but it's still a great moment when you get to the point where calls can be made on the switch.

7 April -- Worked on wiring in the trunk plate today.  One of the circuits on the plate works fine, the other has some issues.  A fair bit of time was spent chasing out the problems in that second trunk circuit and, as usual, came down to relay contact issues.  First there was a lot of crud on the "D" relay contacts, and also those same contacts are not meeting well in the normally closed position.  I still need to tweak those contacts, but at least the problem has been identified.

Both circuits were wired into the terminal block on the switch and it was time for the big test with the working circuit #1, and ... it didn't work!!  I had managed to read the schematic wrong and had the wrong pins for the output of that circuit... I was attached to the output pins of circuit #2.  Some quick work with the soldering iron to swap the leads in question and the trunk came to life.  At the moment I have circuit #1 connected to level 9 of the first selector, so you can go off hook, and dial 9 to access whatever I have the trunk connected to.  I tried it with the real PSTN CO line into the house, a line on the big step switch in the cellar, and a VoIP C*NET line and successfully dialed out on all of those from a station on the still-under-construction switch.  Cool stuff.

In other switch work, I got the microcontroller/interrupter/ringing machine board closer to being ready to install.  A connector for the 12V power that board needs was attached.  I still need to add a connector for the dial tone/busy/reorder tone board that has yet to be built.

15 April -- I was out of town for a few days over the Easter weekend so didn't get much more done on the switch until today.  Today I got the interrupter/ringing supply board mounted and wired into the switch... the dialed stations now ring!  There is also dial tone and busy on the switch, though for now it's from the microcontroller generated tones (200 Hz dial tone, interrupted 400 Hz for busy).  I plan to build up a digital recorder chip board with the old style 600/120 tone on it, but that is yet to come.  But, getting the ringing supply mounted and wired in is a major step.  The switch is nearly fully functional at this juncture.  What remains to be done is primarily the old style tone board, and to wire in the reorder tone for unavailable levels on the selectors.  I'll get some updated photos to post in the next day or so to share.

19 April -- Some photos of the switch as it exists at the moment, taken this afternoon:

View of the back.

Close up of a call up on the switch.
 View from the front.  Equipment compliment across the top (L-R):NE 33014 LF, WE 30200 1st Sel (m'fd 1942!), WE 30200 2nd Sel, WE 31737 Conn.  Bottom row (L-R): PIC interrupter board & ringing supply, WE 30779 trunk plate, AE L/CO plate.

25 April -- The switch is nearly done!  The recorder chip board and interrupter gate was wired up over the last week or so and hooked up to the microcontroller board on the switch frame today and tested.  It works.  The board was mounted to the frame and the switch now has "old style" dial tone, busy, and reorder.

There are various detail things to be done yet, like labeling the terminal blocks, getting a connectorized "dongle" of sorts ready with jacks and screw terminal blocks on it for connecting display phones to the switch quickly and easily, unused selector levels need to be grounded out so they'll go to reorder if dialed, and so on.  However, as it stands right now, the switch is fully operational!

Also over the last week or so I built some small stands to allow wall phones to be displayed on a table and be used.  I am planning on taking a few interesting wall phones to the TCI show with the switch and have them connected and working with it.  Another detail item is to get proper number cards stamped with numbers for all the phones that will be conencted to the switch.

9 May -- The detail work on the completion of the switch continues.  Last weekend I labeled the terminal blocks so I remember what is where on them, and I also mounted the wall phones on the stands that I built and painted.

Today I worked on installing a 25-pair connector to facilitate the hookup of the display telphones, and to also quickly hook it up to the system here at home when the switch is not on the road.  I had a 25-pair jack that had been cut off from its cable so I spliced 20 pairs back onto the jack and mounted it on the switch frame.  I connected the leads to various places in the switch, namely the station and trunk ports.  I am making a small terminal board that will plug into this jack that will contain phone jacks to plug the display telephone sets into.  That should hopefully speed along the process of setting up a display with the switch, without having a bank of jacks permanently mounted to the switch frame to get bashed and battered when the frame is moved.  Also, when the switch is home and connected to the system here, the individual jacks won't be needed.

In other news, I received a C*NET phone call during the week from another switcher who is planning to have a display at the Lancaster, PA show in a few weeks.  He wants his display to interface with mine so he was telling me what he will need from my switch for his machinery.  His display will be controlling yet another switcher's panel switch section.  It should be a fun and interesting show!

14 June -- The Lancaster phone show was last weekend and was a great success.  There were over 70 tables of folks selling and exhibiting telephones and telephone-related items.  The "Switchers' Corner" was a big hit.  There were three switch displays: mine, another small portable step switch with integrated C*NET Asterisk VoIP gear that served as the C*NET gateway to the show, and a revertive signalling display with a "miniature" toll switchboard controlling a panel switch selector.  Many show guests stopped to look, ask questions, pick up a phone and dial, and there were a number of C*NET users from literally around the world that called in to the show through the step switches on display.

Pictured at left is my portable switch on display with the phones that I had hooked up to it.  I also brought some wall phones for which I built special stands so the phones could be displayed on a table.  The surprise of the show, for me at least, was the ribbon I won for the "Most Educational" display. (photo below) It certainly made the last few months of work seem all the more worthwhile.  I still can't believe that I won a ribbon for the first display I have done.

There are more photos of the show posted on the TCI web site:

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