Block detector wiring

[StuartN]

Part of my layout consists of a single track loop and a station which acts as a passing track and therefore has a point at each end. Two trains can go in opposite directions, but only one can run providing the other train is stopped on the opposite platform, and this I can see. Part of the loop is accessible but hidden. I have spent a lot of money on the layout and need to be economical in future.

My first thought is to have 3 aspect signals, the red and green controlled by the point ahead, and the yellow controlled by a block detection device. I will only run the train if the signal is green. However this means that the red and yellow lights can be on at the same time.

Also it seems to me to be a logic question ie

Train detected OR point set against = RED

No train AND point set correctly = GREEN

Any ideas please?

Edited February 14, 2020 by StuartN
Additional info

[The Stationmaster]

Try thinking about it this way -

Train detected or point set against = Red

No train and point set correctly = Proceed aspect 

Situation at the next signal in advance will decide which proceed aspect is shown - i.e. if that signal is at red the proceed aspect will be yellow; if that signal is showing a proceed aspect then the proceed aspect on the first signal will be green.

 

The bit you always need to remember is that the type of proceed aspect any multiple aspect signal can show will be governed by the aspect shown by the next signal in advance (where 3 aspect signals are used).  Look at this page -

http://www.railsigns.uk/info/aspseq1/aspseq1.html

Edited February 14, 2020 by The Stationmaster
Correct typo

[StuartN]

Sorry, but this is too complicated for me.

Also I will only be able to see one signal as the rest of the track, including the point, is hidden.

It occurs to me that logic problems are solvable electronically, but I have no idea what that circuit would look like.

[The Stationmaster]

Let's try again then - assuming you have a crossing loop at your station with a point at each end.  The point will require to be protected by a signal - we'll call it Signal A.  At the further end of the loop where the train rejoins the single line there will be a second signal - we'll call it Signal B.   There will be an an A and a B in each direction if trains in opposite directions are to cross (i.e. pass each other) in the loop/at the station.

 

Signal A will be a 3 aspect signal capable of showing red, yellow, or green.  Signal B need only be a 2 aspect signal capable of showing red or green.   Signal B is in advance of Signal A, i.e. a train running in the right direction will first pass Signal A and subsequently pass Signal B.

 

Signal A needs to be controlled to two states -

1. Danger, when it will show a red aspect, and

2. Proceed, when the aspect it will show is controlled by the aspect displayed by signal B.  If signal B is at danger Signal A will show a yellow aspect,  if Signal B is showing its proceed aspect (which can only be green in this example) then Signal A will also show a green aspect. 

 

Thus the colour of the proceed aspect in Signal A will always be controlled by the state of Signal B.  A very simple way of thinking about it is to regard the signal aspects as being controlled by ordinary switches - Signal A only needs a single pole double throw (SPDT) switch; one way the switch sets signal A to red, the other way it is connected to the switch which works Signal B and that switch feeds the yellow and green aspects on Signal A.   Signal B will have a double pole double throw switch (DPDT). One pole controls the aspect shown at Signal B - either red in one position or green in the other .  The second pole controls the yellow and green aspects in Signal A and it is fed from the SPDT switch for Signal A (when it is set to the 'proceed aspect').  All very simple logic provided you keep in mind that the proceed aspects of a 3 aspect signal are controlled (=switched from one proceed aspect to the other) by the next Signal in advance.

 

Does that now make sense for you? 

[StuartN]

You've got me!

This is what I have. I assume that if there is only one train at the station, then the other is somewhere on the line and so the train at the station cannot move.

But I want to automate it better, and since I might not be able to see the other hidden train, I might easily forget that there is one or maybe one hidden.

[StuartN]

I am thinking of something like this.

Some sort of switch / relay.

If the block detector activates, then red is sent to the signal.

If not, then the frog power is sent which can be either red or green.

Any problems with this?

[Dungrange]

That logic looks fine for a two aspect signal, which only has one proceed aspect: green.  If the block ahead is occupied or the points are set against the train, then the signal will display a red aspect.  Therefore the only condition on which a green aspect can be displayed is if the block occupancy shows unoccupied and the points are set correctly.

 

What are you planning to use for your block occupancy detection?  You've also shown a wire to the common crossing on a turnout, but are you planning for this to actually be connected to the wiring of the frog, or to a micro switch or switch contacts on a point motor?

[StuartN]

The frog wiring is switched at the point motor. The red and green led share this wire but they also return via each side of the track which is DCC powered,

I am asking the question because I have made no idea about the detector or the relay.  I just need to detect a train on the track. In practice, this bit of the layout is not significant as all I have to do is to see if a train has stopped by the station. And I don't want to spend a fortune as this is in some ways a simple experiment.

[Dungrange]

Okay, assuming your signals are designed to operate at DCC track voltage (ie +15V or whatever your system puts out), then I can see how you could connect the lead from one LED to one rail, the lead from the other LED to the other rail, and the common anode or common cathode to the frog.  In theory only one of these two LEDS will have a potential difference across it and therefore only one will be lit.  However, LEDs are designed to work at about 3 volts, so you'll need appropriate resistors in your circuit.

 

Adding in the need for a detector is where things start to become more complicated (and expensive).  You can buy either location occupancy detectors such as Heathcote's IRDOT (InfraRed Detection of Trains) - http://www.heathcote-electronics.co.uk/heathcote_product_index.html or you can buy current sensing devices such as the BD20 from NCE - https://www.coastaldcc.co.uk/products/nce/bd20-block-detector.  If you're looking to detect a train anywhere in a track section, then I think it's a current sensing device that you're looking for.  The NCE BD20 is not the cheapest option if you need lots of train detection, but if you're only looking for one section, then I think it is the cheapest option.

 

If the layout is more complicated than you've shown, then look at Digikejs - https://www.digikeijs.com/en/digital-model-railway-accessories/model-railway-feedback-modules.html (prices vary depending on whether you need LocoNet or other feedback protocols) - but the per output price is less than the NCE BD20.  Another alternative would be the Digitrax BDL168 - https://www.coastaldcc.co.uk/products/digitrax/feedback/bdl168-loconet-occupancy-detector, but I don't see what benefits the BDL168 offers to justify the higher price compared to the range of Digikejs products.

 

Once you've decided on the block occupancy detectors that you plan to use, it should be easier to determine what you require for the rest of the circuitry.  In fact, the instructions that come with your chosen occupancy detector probably has a wiring diagram for what you are trying to achieve. 

[StuartN]

Thanks so much Dungrange for your reply. It was just what I needed.

Yes I know about the resistor - I have used this for my mimic board, so this should be no different. I don't know, but I assume if I buy a proper signal, it will have all this already.

From what you write, I think I need a current sensing device. I assume you think that such a device might well have some sort of relay built in. I will phone CostalDCC on Monday for advice. The NCE makes a little sense as I use a NCE Powercab.

Again thanks.

[Dungrange]

I don't think there is a relay built into the NCE BD20, but it has an output that can switch a relay.  The DCC Concepts website has a link to the NCE product manual - https://www.dccconcepts.com/manual/nce-owners-manual-bd20-block-detector/ , which you might want to have a quick read through before phoning Coastal DCC (or your chosen supplier - Coastal DCC was just the first link I got when typing into Google).

 

Basically, you pass your track feed through one of these devices and when something is sitting in the section drawing current, the BD20 detects that current draw (as long as it is more than a few milliamps) and passes out a low voltage signal that can either be used to light an LED on an indicator panel or act as a switch to change a point motor or activate a relay.

[Junctionmad]

You could “ simulate “ three aspect operation ,  by using timing modules , ie on detecting a passing train the timer shows red , then after a time , yellow then green .  While this will fall down of the train leaves the block after the signal and then stops 

 

 

[StuartN]

I've now received the NCE BD20 and I also downloaded a wiring diagram from NCE showing how to operate red and green signals.

But I need help in the relay(?)

[StuartN]

I've bought the DCE BD20 but I can't get it to work.

I've wired up the red wiring and the red led on the motherboard lights up, but I can't get a led connected to the output to do so.

The blue wiring is the frog wiring going to some 2 aspect signals, yet to be wired.

Any help greatly appreciated.

[Dungrange]

What power supply are you using to power the LED that you are trying to light and what are the requirements of the LED that you are trying to light?

 

The Quick Reference guide (https://www.dccconcepts.com/themencode-pdf-viewer-sc/?tnc_pvfw=ZmlsZT1odHRwczovL3d3dy5kY2Njb25jZXB0cy5jb20vd3AtY29udGVudC91cGxvYWRzLzIwMTYvMDIvQkQyMC1RdWljay1SZWZlcmVuY2UtR3VpZGUucGRmJnNldHRpbmdzPTExMTExMTExMTExMTExMTExJmxhbmc9ZW4tVVM=#page=&zoom=auto&pagemode=) shows a low Voltage power supply (5 - 12V) connected across pins 1 and 4 and an LED with a resistor connected between pins 3 and 4.  Obviously the value of the resistor that you need is dependent on the power supply and whether the LED is designed to work with a 5V or 12V supply.  12V LEDs usually operate at a lower voltage, but already have resistor built in to limit the current draw.

 

Clearly if you are getting a light on the motherboard, then the BD20 is actually detecting a locomotive on the track, so it sounds as though you don't have the correct set up of power supply, LED and resistor or the specifications are incompatible.

 

Once you get the LED working, the next step is obviously to work out how to connect a relay to the detector.  It looks as though pins 1 and 2 provide the logic that should switch a relay.  Have you tried connecting a relay across these pins and does it switch when the BD20 detects something on the track?

[StuartN]

I am using 12v DC for lighting. The signal is made by Traintronic. Bu not yet connected.

The red led on the BD20 lights up whether there is something on thetrack or not.

I haven't bought a relay as yet and was hoping not to hve to,

 

[StuartN]

I have just discovered that the signal is 12v DC and I was hoping to rely on DCC. I have used LEDs on mimic board and wired one side of each LED to frog and the other side to one side or other of track. So if the track is opposite side to frog, the LED lights up. But the signals don't work that way, and I don't know if I need some more kit to make it work.

[Dungrange]

I suspect that you'd have been better asking an electrical question in the wiring section rather than the section for permanent way, signals and infrastructure

 

6 hours ago, StuartN said:

The red led on the BD20 lights up whether there is something on the track or not.

 

Okay, so that implies that the red LED on the motherboard just indicates that the BD20 has power - I'm assuming that it has its own power supply.  The obvious question though is does the BD20 actually detecting something when placed on the track?  Do you know whether the unit is actually working?  I think you need to add in the optional LED indicator so that you know the unit is working first before trying to connect it to your signal.  If you can't get that to work, then you might need to play about with the number of wire loops through the unit to get the sensitivity right.  That seems to vary depending on the power output of your system (or power district if you have intermediate circuit breakers) and the resistance of your wheel sets.

 

4 hours ago, StuartN said:

I have just discovered that the signal is 12v DC and I was hoping to rely on DCC. I have used LEDs on mimic board and wired one side of each LED to frog and the other side to one side or other of track. So if the track is opposite side to frog, the LED lights up. But the signals don't work that way, and I don't know if I need some more kit to make it work.

 

The Traintronics signals seem to require either an on-on switch or DCC Accessory decoder to operate them and they need their own 12V DC power supply.  Obviously connecting each signal to a DCC accessory decoder would allow you to change the aspect by calling up the accessory address (just like throwing a point) but that's not what you're looking to do.  The signal therefore appears to work in the way you want to use it by being connected to a 12V DC power supply (not your DCC track bus or the feed to your frog) and a separate switch allows you to change between the red and green aspects.

 

Again, I think you need to prove that the signals can operate the way that they are intended to by throwing a switch.  I suspect that it's just a Single Pole Double Throw (SPDT) switch that you would need for this test.

 

Once you know that the BD20 works and the signal aspect can be changed by the flick of a switch, you then need to replace the switch with a relay board of some form, which will be thrown by the output from the BD20.

 

I think you have three logic scenarios:

Signal A = Red and Signal B = Red - You want this when the BD20 detects something irrespective of the position of the point.

Signal A = Green and Signal B = Red - you want this when the BD20 doesn't detect anything and the point is set to the route from Signal A

Signal A = Red and Signal B = Green - you want this when the BD20 doesn't detect anything and the point is set to the route from Signal B.

 

This means that I think the SPDT switch that you're meant to use to change the signal aspect needs to be replaced by both a relay attached to the BD20 and a set of switch terminals on the point motor (not the ones that are used to power the frog).  However, I'm not clear on whether you just need one set of terminals on the point motor for both signals or one set per signal.

 

Both signals need to be connected across the terminals of a relay connected to the BD20 but also through a set of terminals on the point motor switch - I'm just not quite sure which way to wire these but the position of the relay and the point motor switch should give you the logic that you need to derive the correct signal aspects.  I think the important point is that nothing here is connected to DCC (apart from the power feed looped through the BD20).  Power flows from your 12V power supply through the switch, relay and signal and back to the power supply. 

[StuartN]

I think you have three logic scenarios:

Signal A = Red and Signal B = Red - You want this when the BD20 detects something irrespective of the position of the point.

Signal A = Green and Signal B = Red - you want this wheThe cheaper the better. the BD20 doesn't detect anything and the point is set to the route from Signal A

Signal A = Red and Signal B = Green - you want this when the BD20 doesn't detect anything and the point is set to the route from Signal B.

 

Exactly right.

 

So do I only need to buy a relay and if so, can you recommend one? The cheaper the better.

Also I am trying to mock up the BD20. Will get back.

[Dungrange]

I can't really recommend a relay.  Although we have several relays on our club layouts, the component specification and wiring is something that I leave to the experts - that's not me.

 

However, I think you need a Double Pole Double Throw (DPDT) relay - ie one that has two sets of switch terminals.  As you'll only be switching mA at 12V DC, I don't think it should be too expensive, as you're not switching a lot of power.  I think you are looking for the non-latching type, so it's only 'on' when something is detected and automatically goes 'off' as soon as nothing is detected.

 

I think you will also need two sets of switch terminals on your point motor in addition to the ones that you are using to switch the frog power.  That may mean connecting another DPDT microswitch to your point motor since I'm not aware of any motors with three sets of switch terminals.

 

If my logic is correct, you need to connect one side of your 12 V DC signal power supply to the two common terminals on the DPDT relay.  The two switch outputs that will be connected when the BD20 detects something should be connected to the red LEDs on your signals.  The first switch contact goes to signal 1 and the second switch contact goes to signal 2.

 

The two switch outputs on the relay that will be connected when nothing is detected need to be connected to the two common terminals on the DPDT point motor microswitch.  The four outputs on that switch will then be connected to Green aspect on signal 1, Red aspect on signal 1, Red aspect on Signal 2 and finally Green aspect on signal 2.  Note that the Red and Green are reversed for the second signal.

 

The other side of your 12V power supply for the signals is connected directly to the signals.

 

That therefore means that if the BD20 detects anything on the line ahead then the power will flow from your supply through the relay to the red LEDs, bypassing the point motor microswitch, because the setting of the point is irrelevant.

 

However, if nothing is detected by the BD20, then the relay will be 'off' and the power will flow from your supply through the relay to the point motor microswitch which will determine which LEDs are lit.  These should be either Green 1 and Red 2 or Red 1 and Green 2 if you've wired them correctly to your microswitch.

[StuartN]

Thanks for this. But I am having to re-read it a few times to make absolute sense of it.

Is there any chance of doing a circuit diagram?