Reversal Module LGB 55080

[Gizzy]

I recently acquired one of these modules from Zerogee, and wired it up to the reversal chords at Weybourne.

All is working well but I am intrigued as to how it does it.

When I use the Universal Remote to drive a train from Sheringham to Weybourne, via the reversing loop, I use the convention that the right button moves the train to the right and ditto for the left button, when viewing from the lawn.

However, one the train has looped via Weybourne and heading back to the terminus at Sherringham, those buttons on the Remote are now transposed back to front in my thinking.

I guess this is something the chip in the loco processes and actions, as the signal on the track must stay the same but somehow, some protocol between the reversing module and the loco must detect that the signal has 'inverted'.

Could someone enlighten me how this is actually done? I'm wondering if I could put an LED indicator across the output of the module, to show a change is detected....

 

[Zerogee]

Hi Gizzy! In all MTS operation, the control is always relative to the LOCO, not the track. One button drives the loco FORWARDS, and the other backwards - so if the loco turns round in the reverse loop, the command to the loco is still "go forward", which is what it continues to do. You're still thinking in the "analogue mindset", where direction of movement is controlled by track polarity; with MTS, you need to think of yourself as the engine driver in the cab!
I know that isn't a a technical explanation of HOW it does it, just accept that magic happens in the decoder.....

Jon.

 

[Gizzy]

That's a good explaination Jon.

I'll have to think right button is forward and left button is backwards from now on....

 

[Zerogee]

Yes, that's the way to look at it; in fact the little loco icons used to label the controller buttons indicate this. It's really the same as operating a radio-controlled model - when when the boat/plane/car/whatever is coming towards you the controls seem "crossed over" because the operator's left is now the model's right, and vice-versa. As long as you always think of yourself as in the loco's cab, it will become intuitive.
Jon.

 

[muns]

The 55080 works by detecting a short circuit across the input connector. This occurs when you run a train into the reverse loop and the polarity of the loop is incorrect for the running direction. The module then switches the polarity of the loop and every thing is fine again and the train continues. When the train leaves the loop, another short circuit will occur, causing the module to again switch the loop polarity. The switching occurs faster than the short circuit detection time of the central station thus avoiding the central station tripping.

All DCC loco decoders have the notion of forward and reverse regardless of how the loco is facing on the track.

 

[Gizzy]

The 55080 works by detecting a short circuit across the input connector. This occurs when you run a train into the reverse loop and the polarity of the loop is incorrect for the running direction. The module then switches the polarity of the loop and every thing is fine again and the train continues. When the train leaves the loop, another short circuit will occur, causing the module to again switch the loop polarity. The switching occurs faster than the short circuit detection time of the central station thus avoiding the central station tripping.

That's interesting Mark. Are you saying that the output of the 55080 unit is DC? When one uses the term polarity, I'm thinking +ve and -ve. As I understand DCC it is a signal superimposed on a carrier wave, and if I measure voltage, I get an AC reading on my meter.

You may have surmised that I am thinking of connecting a LED signal to the output, and that is the reason for asking my question....

 

[Zerogee]

Actually, that's a very good point, Gizzy! I had also always assumed that MTS/DCC uses AC to the tracks, and while I presume that you can still have a "short" with AC if you join the live and return wires (which is effectively what the loco wheels are doing when they bridge the insulated gap and trip the reverse loop module), I'm not quite sure either of why the polarity needs to then be switched.... this is when I realise that the theoretical side of my electrical knowledge is rather rusty...!
Can anyone explain this in words of one syllable for those of us who are "hard of thinking"?

Jon.

 

[ntpntpntp]

The DCC signal is an alternating current in that it's a waveform that swings either side of zero volts, but it's not quite the same as the usual smooth constant frequency sine-wave AC that most people think about when they think of AC. Neither is the DCC signal simply "superimposed" on a constant carrier wave, but to be honest it's probably a reasonable way to think about it.

If you want to try and get your head round it, try this: http://en.wikipedia.org/wiki/Digital_Command_Control < Link To http://en.wikipedia.org/w..Digital_Command_Control

If you get the two wires (or rails) of the electrical circuit crossed (as happens with a reversing section) then you get an out-of-phase short circuit, and as Mark explained that's what the reversing module watches for and corrects very quickly as your loco crosses the isolated joints into the reversable section of track.

 

[Gizzy]

The DCC signal is an alternating current in that it's a waveform that swings either side of zero volts, but it's not quite the same as the usual smooth constant frequency sine-wave AC that most people think about when they think of AC. Neither is the DCC signal simply "superimposed" on a constant carrier wave, but to be honest it's probably a reasonable way to think about it.

If you want to try and get your head round it, try this: http://en.wikipedia.org/wiki/Digital_Command_Control < Link To http://en.wikipedia.org/w..Digital_Command_Control

If you get the two wires (or rails) of the electrical circuit crossed (as happens with a reversing section) then you get an out-of-phase short circuit, and as Mark explained that's what the reversing module watches for and corrects very quickly as your loco crosses the isolated joints into the reversable section of track.

Thanks Nick, I think I've got my head around it.

My understanding now, is that you have pulses sent to the decoder, as per the pulses diagram in your linky;


These pulses are suddenly inverted when the short occurs, so you would get a high positive pulse and a high negative pulse at the same instant, creating the short circui,t which is then detected and corrected by the LGB 55080....

 

[Zerogee]

Thanks Nick, that Wiki link and your explanation helped a lot - it all makes some kind of sense now! So I assume that when we talk about the reverse module switching "polarity", what it's actually doing is making sure that the digital on/off signal is "in phase" rather than out. If at any given microsecond one rail is "+" and the other "-", that explains why you would still get a short if you had an UNinsulated reverse loop.

Jon

Edit - I posted this at the same time Gizzy was writing his reply above, I think we're both saying the same thing....?

 

[mike]

its a monkey train system, little monkeys drive the locos, in the handset are smaller monkeys relaying messages to the point control monkeys..

 

[steve parberry]

The 55080 works by detecting a short circuit across the input connector. This occurs when you run a train into the reverse loop and the polarity of the loop is incorrect for the running direction. The module then switches the polarity of the loop and every thing is fine again and the train continues. When the train leaves the loop, another short circuit will occur, causing the module to again switch the loop polarity. The switching occurs faster than the short circuit detection time of the central station thus avoiding the central station tripping.

That's interesting Mark. Are you saying that the output of the 55080 unit is DC? When one uses the term polarity, I'm thinking +ve and -ve. As I understand DCC it is a signal superimposed on a carrier wave, and if I measure voltage, I get an AC reading on my meter.

You may have surmised that I am thinking of connecting a LED signal to the output, and that is the reason for asking my question....

All you need giz is a bridge rectifier or four diodes and it will give you a nearly true dc output.

Works for me

 

[Gizzy]

The 55080 works by detecting a short circuit across the input connector. This occurs when you run a train into the reverse loop and the polarity of the loop is incorrect for the running direction. The module then switches the polarity of the loop and every thing is fine again and the train continues. When the train leaves the loop, another short circuit will occur, causing the module to again switch the loop polarity. The switching occurs faster than the short circuit detection time of the central station thus avoiding the central station tripping.

That's interesting Mark. Are you saying that the output of the 55080 unit is DC? When one uses the term polarity, I'm thinking +ve and -ve. As I understand DCC it is a signal superimposed on a carrier wave, and if I measure voltage, I get an AC reading on my meter.

You may have surmised that I am thinking of connecting a LED signal to the output, and that is the reason for asking my question....

All you need giz is a bridge rectifier or four diodes and it will give you a nearly true dc output.

Works for me

I was looking for an easy and cheap way of changing a signal aspect with the 55080 unit Steve.

With a train in the reversing loop, I was hoping the output could be used to change a bi-colour red/green LED using diodes, but as MTS works on coded pulses, I don't think this is feasible with diodes....

 

[Eaglecliff]

Having read the above, I'm glad I've stayed with analogue... my brain hurts!

 

[Zerogee]

Having read the above, I'm glad I've stayed with analogue... my brain hurts!

I think the important point is that we don't NEED to understand it, all we need to know is that we push buttons, magic happens, and our trains go!

Just like I'm now typing stuff on my computer, without needing to know what's actually going on inside it.

Some bit of knowledge of how the magic actually works is interesting if you like that sort of thing (hence Gizzy's question) but it certainly isn't necessary in order to use and enjoy all the benefits that DCC/MTS gives!

Jon.

 

[muns]

I am sorry to have raised some confusion when I refererd to the reverse loop module changing the rails "polarity", maybe I should have said it changes/reverses/swaps the rails power feed.

 

[Gizzy]

I am sorry to have raised some confusion when I refererd to the reverse loop module changing the rails "polarity", maybe I should have said it changes/reverses/swaps the rails power feed.

No problem mate, we cleared up the confusion in the end?
Although perhaps not for Eaglecliff!

MTS is quite a complex subject, but it's something I'm interested in. But as Jon (Zerogee) mentioned, you don't need to know this techie stuff to make MTS work.

For example, not many here will know how the engine in their car works but they can still drive it!

Thanks Mark, and Nick for your contributions....

 

[ntpntpntp]

I was looking for an easy and cheap way of changing a signal aspect with the 55080 unit Steve.

With a train in the reversing loop, I was hoping the output could be used to change a bi-colour red/green LED using diodes, but as MTS works on coded pulses, I don't think this is feasible with diodes....

If the point on your reverse loop is motorised, you could use a bridge rectifier (or 4 diodes) to derive some DC power from the track, then use a point motor accessory switch (12070?) to control a red and green LED or a bi-color LED (one of the 3-lead types with a common anode or cathode). Use a suitable series resistor for current limitation of course! You might want a smoothing capacitor on the DC side of the rectifier, but it won't need to be a big-un to drive an LED or two.

Unfortunately the 12070 puts the price up a bit, but you have the convenience of a locally track-powered signal - no need to run DC power wiring out to the signal.

 

[Gizzy]

I was looking for an easy and cheap way of changing a signal aspect with the 55080 unit Steve.

With a train in the reversing loop, I was hoping the output could be used to change a bi-colour red/green LED using diodes, but as MTS works on coded pulses, I don't think this is feasible with diodes....

If the point on your reverse loop is motorised, you could use a bridge rectifier (or 4 diodes) to derive some DC power from the track, then use a point motor accessory switch (12070?) to control a red and green LED or a bi-color LED (one of the 3-lead types with a common anode or cathode). Use a suitable series resistor for current limitation of course! You might want a smoothing capacitor on the DC side of the rectifier, but it won't need to be a big-un to drive an LED or two.

Unfortunately the 12070 puts the price up a bit, but you have the convenience of a locally track-powered signal - no need to run DC power wiring out to the signal.

You've just posted my Plan B Nick!

I have a couple of the 12070 switches on point motors for just that eventuality, to operate some Playmo signals that I am yet to convert....

 

[steve parberry]

For me its just the bridge rectier and resistor feeding the power to the aux switch and then feeding the leds.