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Dapol signal and Hornby decoder


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I've just received one of the new Dapol OO LMS motorised signals. Very nice it is too.

I''m having problems connecting it to a my DCC system. Any help, much appreciated.

I use Hornby decoders with Elite and Railmaster. All works OK - points are working nicely from the software.

The Dapol signal only has two switching wires. Apparently on each pulse the signal activates i.e on the first pulse the arm raises, on the second the arm lowers. OK, so the Hornby decoder output has 3 terminals - Common, + and -. Is this just not going to work?



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Please contact Dapol outlining your problems and operating needs, and ask for their solution. It has been discussed on the Dapol part of RMWeb, but the thread seems to have generated a lot of heat and only a certain amount of clarity around the issue.



Whilst waiting for Dapol's solution, the simplest idea I've seen so far is a relay attached to your DCC turnout decoder, such that the relay pulses on/off briefly as the decoder operates. (ie. Relay appears same as a solenoid turnout motor and operates for a brief pulse of power).

The relay contacts are used to connect the two wires on the Dapol signal briefly (ie. the same job as a push button), which will then change the arm position.

Ideal relay would be connected to the + and - of the decoder, and thus will operate in either direction of turnout throw - you will have to experiment with this to see if it works, some relays are fitted with diodes which make them only operate in one direction of current flow.


If it does work, you won't have a consistant movement of the signal, ie. "thrown" won't necessarily mean "up". Instead it will be random when you change that accessory's state, based on the state last time you turned the layout power off. A push button switch could be added to move the signal without the decoder, and thus get it back into "sync".



Alternatively and much more drastic, I've seen two proposals for replacing the small electronics board inside the Dapol signal. Clearly you throw out the Dapol guarantee in doing such a thing. If you get to that point, I'd recommend buying signals from someone else, with a control system which works for your needs - there are plenty of people offering to custom build signals.


- Nigel

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A slight variation on Nigel's siuggested solution: Applicable if you have 2 (or more) Dapol signals covering a single track line - with at least one for each direction:

Use the 'left output' of the accessory decoder (eg No2. Left) to PULSE (via that relay) the Signals (eg Home and Distant) for 'Left to Right' along the line, and similarly another relay, buit connected to the 'RIght' output (Eg 2 Right) to the Signals allowing trains from Right to Left.

NOTE: that although onyl 1 relay would be needed per direction, it would be best (if not essential) tha the 2 or more signals for each direction used SEPARATE contacts on the relay: ie a SPST or SPDT relay for 1 signal, but a DPST/ DPDT relay for 2 signals BECAUSE you cannot tell where the yellow -'pulse' leads are connected to, inside the unit, compared to the externally applied power on th eother leads

Now, in operation: PULSE LEFT BUTTON for a left to right route .... each pulse will change the state. PULSE RIGHT BUTTON for right to left route.


Moving on from this, it might work to use 2 signals, one for each way, and off 1 DP relay: each pulse, both signals will change .... the trick being to CONNECT the 2nd signal when in the opposite phase. - and then hopefully they'll STAY out of step 8-)


(I only have 1 signal at present)

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Keith asked:

How do you get all your signals to show stop at the same time, as they need to with a train in the section.

On a small layout, such as a TrackPlan Oval, without 'real distances' and a busy schedule - 1 engine in steam - at least its better than no signals? - but your comment only applies to the latter suggestion: the first suggestion will ALTERNATE between stop and go with each (Left) [distant and home >] ... [or Right]. [distant and home <] .. button push (connected when in-phase, they should remain in-phase] quite independantly - so both directions may be at STOP ... or GO (no interlock).


I'm not advocating it meets UK mainline standards, but it would require only 1/2 decoder output-pair 'per direction' and with some degree of logic behind it ...

(In 'early' LGB digital,DCC, functions 2-8 were sent by repeated pressing of the F1 key - 'LGB Serial Mode'.)


With their circuitry, it is important that the yellow wires, of each individual signal, are isolated from everything else (since they are presumably at either '0v' or '3.3V' wrt IC ground - but due to the matching colour 'ac power' wires and the bridge rectifier, are 'somewhere between' the ext.power rails - and therefore must NOT be commoned with any other signal's wires.

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