3-way switching/diode matrix question

[spikey]

 

I currently have a set of three storage loops (those marked with red dots above), access to which is via a three-way point controlled by push buttons and a simple diode matrix. and all is well.  Or rather it was until I realised that if I added a double slip as shown, I could squeeze in a fourth loop as above. 

 

The short siding to the left already exists and it's very handy, with access to it being off the uppermost of the three existing loops via a left-hand point, which the proposed double slip would replace.  That LH point is currently switched via a SPDT momentary switch, and from an operational POV, that plus the push-button selection of the three loops all works very well operationally.

 

However, if I replace that LH point with a double slip, how on earth do I organise the switching for it so that a route through it may be selected simply, and with the minimum complexity added to my control panel? 

[RJS1977]

By coincidence, the push buttons should be where the dots are on your plan!

 

The push button on the short siding should be wired in parallel with the middle PB on the 3-way point. The point motor at the right hand end of the double slip should be wired in parallel with the point motor for the top of the 3-way point, and the point motor at the left hand end of the double slip should be wired to the two push buttons to the right of the DS.

 

[spikey]

18 hours ago, RJS1977 said:

By coincidence, the push buttons should be where the dots are on your plan!

 

They are, actually!  Unfortunately my brain's currently unable to process your suggested way of solving the problem, but I'm greatly encouraged by how a simple solution seems to be possible.  Two cups of coffee in the morning and a bit of peace and quiet should let me get my head round what you say.  Thanks

 

EDITED TO ADD that despite several hours' pondering, I'm still struggling with your suggestion.  Sorry if I'm being thick here, but for one thing I don't understand "The push button on the short siding should be wired in parallel with the middle PB on the 3-way point."  To what purpose?  Surely if the two push buttons are wired in parallel, they both simply switch the 3-way?

 

Whatever, I need to sit down with a template of a double slip and do myself a sort of logic diagram showing which solenoid needs to be fired which way for each of the four possible routes through the point, then try again to relate that to your suggested way of doing the switching.

Edited January 13, 2020 by spikey
Continued confusion

[RJS1977]

 

Sorry, what I should have said is that the top half of the three way point, and half the double slip act as a crossover. Therefore the point motor for that half of the double slip (right hand tie bar - coils 7&8 above)  should be wired in parallel with the point motor for the top half of the three way point (coils 3&4), meaning that the 'straight on' push button (D) on the three-way and the push button on the siding  (A) perform the same function, so can be wired in parallel. You may however find you need a slightly higher AC voltage to your CDU as three point motors (1/2, 3/4 and 7/8) can be fired simultaneously - I have a similar situation on my layout and need to upgrade the power supply to the CDU from 15VAC to 20VAC, as recommended by Gaugemaster.

 

The easiest way to remember how a double slip works is to think of two points positioned tiebar end to tiebar end, then overlap them on each other.

[DCB]

@RJS1977   It needs more thought.    You need to fire 1/3/6/8  or 1/3/6/7 to get to the top loops.  That will mean a lot more power, bigger capacitor or higher voltage and will put a lot of strain on the tie bars 3 way point when selecting the bottom two roads.  I have had the blades rip out in the past.  I solved it by putting  another two point motors in circuit when only two points throw together to balance the load. I use any old point motor past its prime which still has one good coil as a dead load.

 

More seriously and there is no way to select the route from the kick back siding to the top or one down loop.    I have a set up where the top loop has a kick back which is fairly simple but the double slip really ramps up the complication.

 

I would consider having it as two separate circuits, blue and red as per my drawing.   If you lose the opportunity to run into the kick back from one loop and depart on the other then its fairly simple, but not as simple as moving the kick back point to the top loop only.  That way you can run through and reverse he tail of a long train into to kickback out of the way.   I try to arrange it so the short top loop has kick backs both ends so I can saw a long train into the top road without any curves, so the shortest loop actually takes the longest trains.  Worth a though? 

[Robert Stokes]

You could use a 4-way rotary switch to control access to each of the loops. The rotary switch would operate the two point motors on the 3-way point and the one at the right-hand end of the DS. You then use the SPDT switch to control the left-hand point motor on the DS to allow an engine to run from the short siding into either of the top two loops.

 

Robert

[RJS1977]

6 hours ago, DavidCBroad said:

@RJS1977   It needs more thought.    You need to fire 1/3/6/8  or 1/3/6/7 to get to the top loops.  That will mean a lot more power, bigger capacitor or higher voltage and will put a lot of strain on the tie bars 3 way point when selecting the bottom two roads.  I have had the blades rip out in the past.  I solved it by putting  another two point motors in circuit when only two points throw together to balance the load. I use any old point motor past its prime which still has one good coil as a dead load.

 

More seriously and there is no way to select the route from the kick back siding to the top or one down loop.    I have a set up where the top loop has a kick back which is fairly simple but the double slip really ramps up the complication.

 

I would consider having it as two separate circuits, blue and red as per my drawing.   If you lose the opportunity to run into the kick back from one loop and depart on the other then its fairly simple, but not as simple as moving the kick back point to the top loop only.  That way you can run through and reverse he tail of a long train into to kickback out of the way.   I try to arrange it so the short top loop has kick backs both ends so I can saw a long train into the top road without any curves, so the shortest loop actually takes the longest trains.  Worth a though? 

 

I was thinking of having 5/6 separate to 1/2,3/4,7/8. So you press one button to energise coils 2,4,7 to come over the crossover, and a second PB to energise either 5 or 6 for bottom or top road.

[Andy Reichert]

Think of the problem as a set of routes, not destinations.

 

There are 4 routes from the 3 way turnout to sidings 1-4. And there are two routes from the kick back to sidings 3 or 4.

 

For each route you need a separate route push button (6 in all).  The wire the diodes from each push button to operate the appropriate turnouts to the direction that route requires.  Just note that you can only push one route button at at a time.

 

Andy

[PSi]

Would pressing two buttons -- like in NX system simultaneously be an acceptable solution?

 

Double slip may mentally  be "broken up" into two ordinary switch, like below:

 

 

I'm using nomenclature used in Finland (and probably in Germany) to denote different ends of a double slip. The letters within coils of twin-coil motors will cause route to enter or exit at the track end with the same letter. As one splits the double slip into to two ordinary switches, the coils "mentally" look like shown above. Should you know this beforehand, then I apologise. As you mentioned that you already used a three way centre-off switch for the spur you would have connected the switch to the point motor denoted with letters a and b. The other motor you would connect to your diode matrix as an ordinary turnout.

 

Now, if the pressing of two buttons atthe time is ok with you, then you could do something like what is shown below. It has in a way two diode matrixes, one at the "plus" side of the turnout motors and another at the "minus" side of the point motors:

 

Note that the point motor V3 a/b is "upside down". By pressing button A or B at the same time as pressing button 1...4 will set the route between those buttons. Turnout V2 is thrown to direct route when the turnout V1 is set to diverging route. This is only to consume some energy from the capacitor discharge unit to prevent point blades of turnout V1 becoming loose from the throw bars, as suggested by DavidCBroad (I too have done that mistake myself at Tapiola club, see photos at https://taprk.org/eng/show/prp_2002/ )

Now there will be at minimum 2 and at maximum 4 motors operating at one time. Due to having diodes at the "plus" and "minus" side they will tax more compared to single sided diode matrix. If you can invest to another capacitor discharge unit, you could then feed button A with one CDU and the button B with another and have the minus sides tied together (make sure this is ok from the manual of the CDU of your choosing). This way the CDU for button A will fire 2 or 3 motors at one time and the CDU for button B will always fire two motors at one the time.

 

I have not double checked the diagram, so beware of typos...

 

Ah, and always use protection diodes or snubber diodes across the motor coils -- and beware of the polarity of point motor V3 a/b.

 

pekka

 

Edited January 27, 2020 by PSi
Typos in drawing legends.

[John ks]

I don't think you can get from A to 4 without the extra diode circled in red in the Right Hand drawing

If you would like all your point motors with the common facing up then In the left drawing I have flipped the V3 a,b point motor

Edit. By flipping V3ab it is set wrong for routes B3 & B4, a fix is about 8 posts in the future

I have also adder the choice of 2 buttons (circled in red) OR a SPDT switch (circled in blue), this will work if don't want to flip point motor 3A a,b.

 

 

John

 

 

Edited January 29, 2020 by John ks

[PSi]

John ks — thanks for the addition of the missing diode! I did have a strong feeling that I missed something

 

Are you quite sure about the swapping of the point motor V3a/b? I have my suspicions...

 

Replacing buttons A and B with a toggle switch is a good addition, especially if buttons A-B and buttons 1-4 are far apart and the hand span is not long enough and the walkaround loco controller or tea mug is in the other hand... With Siemens mosaic panels I've seen the mosaic cover removal magnet being parked over a turnout group button to allow turnouts be thrown with one hand.

 

I had a dream of adding flank protection to the plan (i.e. tying coils V2+ and V3a somehow together), but run into difficulties. I trust it could be done with point motors having no common lead, like Peco, but i just cannot get it right. One should always have equal amount of diodes for each simultaneously turning coils, else the one with less diodes will get most of the juice from the CDU.

 

Again — thanks for the correction

 

pekka

 

[PS: is it customary here at RMweb to a) replace (or try to replace) incorrect schematic on previous message with a corrected one, or  b) add a new schematic to later message, or c) leave it as it is?] / PSi

 

 

Edited January 28, 2020 by PSi
typos again

[Suzie]

You just need to look at this as being a group of (relatively) simple things.

 

1. The right hand motor of the double slip can just be paralleled with the 'top' motor on the 3-way point to form an effective crossover. This way the double slip will always be set to accept trains from the 3-way when the top route is set through the 3-way point - at all other times the spur siding will be selected instead allowing parallel operations if required.
2. The left hand motor of the double slip should be treated as if you have just added a point to the top loop to add and extra 4th loop.
3. You just need to add the two buttons that provide routes from the spur to the two top loops, these buttons will just set the two motors of the slip (and will provide flank protection because they will operate the parallel motor on the 3-way that is set up as a crossover).

[John ks]

Deleted post, mistakes in logic

John

Edited January 28, 2020 by John ks

[John ks]

3 hours ago, PSi said:

John ks — thanks for the addition of the missing diode! I did have a strong feeling that I missed something

 

Are you quite sure about the swapping of the point motor V3a/b? I have my suspicions...

 

Replacing buttons A and B with a toggle switch is a good addition, especially if buttons A-B and buttons 1-4 are far apart and the hand span is not long enough and the walkaround loco controller or tea mug is in the other hand... With Siemens mosaic panels I've seen the mosaic cover removal magnet being parked over a turnout group button to allow turnouts be thrown with one hand.

 

I had a dream of adding flank protection to the plan (i.e. tying coils V2+ and V3a somehow together), but run into difficulties. I trust it could be done with point motors having no common lead, like Peco, but i just cannot get it right. One should always have equal amount of diodes for each simultaneously turning coils, else the one with less diodes will get most of the juice from the CDU.

 

Again — thanks for the correction

 

pekka

 

[PS: is it customary here at RMweb to a) replace (or try to replace) incorrect schematic on previous message with a corrected one, or  b) add a new schematic to later message, or c) leave it as it is?] / PSi

 

 

I think your suspicions are well founded, after studying the circuit it looks like V3ab is set the wrong way when routes B3 or B4 are set

John

[PSi]

Hmm... I don't think so.... I know I should have marked the coils to follow the track letters, but being lazy I left the coil letters as they were:

 

coil "a" leads to track "B" and coil "b" leads to track "A". Sorry!

 

I know now that I should not have done it the way I did. If I may borrow the words of Spike Milligan: "It's all rather confusing, really!"

 

Suzie: Yes — but I would so much hate to add buttons in between and ruin the NX idea

 

pekka

[Suzie]

Two buttons per route will work for NX rather than the single button.

[John ks]

I think I got it sorted?????

 

The 2 examples are the same but with the A/B switch indifferent positions.

The red lines show the current path & the active coil is highlighted in yellow.

The A/B switch is a DPDT(2 halves shown separately for ease of drawing)

In the B position Pressing 1 or 2 has no effect

 

 

 

Edited to add the following

Much simpler matrix 

Buttons under A for routes from A & buttons under B select routes from B

If you want to multiple CDU then provided the (-) of the VDU is connected straight through the VDU then you can connect any VDU to any 1 or more of the point motors

 

Provided I haven't missed something then is should be possible Shunt from B to 3 or 4 at the same time as shunting from A to 1 or 2

 

John

Edited January 29, 2020 by John ks

[PSi]

John, you are preytty good with this – aren't you

 

Excellent!

 

Looking at this now, the system has departed from the NX into something different but rather elegant!

 

If I should do this for myself I'd rather have the toggle switch between buttons A and B to select the "end". I do hope the original writer – Spikey – has enjoyed this as much as I have!

 

pekka

Edited January 29, 2020 by PSi

[Suzie]

How about this one if you want to go back to NX. Just press an alphabetic button for entry, and a numeric button for exit (or vice versa).

 

 

B-1, B-2, 1-B and 2-B are obviously invalid routes that will always route to A by default. It can be tweaked a bit such as for example paralleling V2 with V3ab and removing the V2 diodes to provide flank protection, but it might be a bit counter intuitive. The starred diodes could be replaced with links too if you want to economise on diodes.