Any swiss signal geeks out there? I have a puzzle, having spent some time researching, I think I have nailed the 'traditional' home and distant signalling aspects, bar one!

Where there is a home and distant signal on the same post, and the home is at danger (red), sometimes the distant signal is blank (no aspect shown) and sometimes it shows the caution next signal at danger aspect (two horizontal ambers). I cannot fathom any logic for the difference, and have even seen both examples on different signals at the same location.

I will probably just go with which ever variation is easiest to wire up and control. Curiosity however is bugging me. 

Anyone any ideas? 

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l’m not familiar with Swiss sigs but it sounds like the style of many (US) systems.

First 3  Swiss Sig questions
1. are you saying that all sigs have 2 heads ?

2. Stop is single red.  Caution ( UK distant ) is red+ yellow (2horiz yellow lights)

3. So what aspect is shown for Clear ?

US Current practice 

There are some variations ( as always ) the current norm is 
each signal has 3 heads vertically aligned on the post 

Stop = 3 vertical red lights 

Proceed at caution next signal at Stop = Yellow over Red over Red 

Clear = Green over Red        Before we get swamped by mails listing options I advice.  There are numerous variations on this aspect to send information to the driver using combinations of the upper two heads however the bottom head is ALWAYS RED.    

I.e. Fail safe when faced Single RED = STOP 

Look forward to your answer to my question 3 


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Hi John, 

Rather than me trying to explain it the following link has a good explanation as they are quite complex at first sight:

If you read / scroll down to the section titled "Main and distand signal on the same mast" you can see my query, example a and b both mean stop at the signal, but the distant signal head can either be lit with a caution aspect, or dark. But it doesn't tell you what dictates whether the distant head is lit or not. Looking at Swiss railway videos and photos you see both examples everywhere and there is no obvious reason, at least not to me.

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Ok, I'd like to think I don't fall into the Swiss signalling geek category, but none-the-less I too have been contemplating the lamp-on/off case where a distant (Vorsignal) is on the same post as a stop signal (Hauptsignal). I have this case on my planned layout.

The understanding I have is that it’s a choice, no specific rule (see below). The only requirement is that when on the same post, the distant (Vorsignal) must show caution (or be extinguished) if the stop signal (Hauptsignal) shows danger, even if the Vorsignal could otherwise show a different aspect.  This is like UK practice; even if a distant signal is pulled off by the box in advance, a slotting mechanism is used such that the distant will stay on whilst the stop signal on the same post is on. 

Taken from Signalbuch der Schweizerischen Bundesbahnen;
1) "Das Vorsignal zeigt jedoch Warnung solange das an gleichen Traeger befindlche Hauptsignal Halt zeigt."
--> Which translates as "However, the distant signal shows a warning as long as the main signal on the same carrier shows a stop."
2) "In den von der Betriebsleitung bestimmten Faellen koennen die Vorsignal lichter geloescht sein, solange das am gleichen Traeger befindliche Hauptsignal Halt zeigt."
--> Which translates as "In the cases determined by the management, the distant signals can be cleared [extinguished] as long as the main signal on the same carrier shows a stop."

The same book also reveals that the distant must be extinguished if the Hauptsignal is showing proceed aspect 6, i.e. 2 ambers. Perhaps a total of 4 amber lights was considered excessive?

Hope that helps,
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Hi Rob, 

Thanks for that, excellent feedback. l can exercise my management determination to set up as I see fit, or which ever is simplest. I will probably go with the distant extinguished on danger as it will be easier to control using infrared detection relay units. I'm amazed the normally well ordered, strictly by the rules swiss would leave more than one option for a given situation, guess there is an underlying reason or design basis for it somewhere in the ether.

Out of curiosity how are you planning to control your signals? On my old layout I used toggle switches or rotary switches for each head depending on the number of aspects appropriate for the location and route options, with the infrared detectors setting back to danger as the train passes. For my new layout I have a rather ambitious plan to automate them based on point/route settings and following signal aspects. Not quite sure yet whether to use relay logic or something software based. DCC Concepts have some nifty new relay units that would do the job but the number I would need for the whole layout is probably going to be prohibitively expensive... 
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Hello Alastair,

I read quite a while ago that the aspect to be shown on a Vorsignal (probably Hauptsignal too) is send in a serial form using wiring shared with the lamp power. Relays are (were) used and that explains why the lamps are momentarily (but observably) extinguished between aspects. I can only guess that the option to extinguish the Vor- amber lamps when the Haupt- shows halt is an option for simplicity, perhaps like in your case, associated with this means of control. I believe that leaving the Vor- ambers on is more common (well for 70's when my layout will be set) so will go for that.

A few years back I experimented with TI MSP430 MCUs for signal control. This means I could emulate the observable fade out of the lamps, the pause mentioned above, and observable fade in. I think the fade out/in is simply due to running the filament lamps below rated voltage for life-time reasons. I could also (though did not) emulate the reduced night time brightness.  In my case I have just two signals, a three aspect Haupt and a three aspect Haupt- plus 4 aspect Vor-signal. These are at opposite ends of the station. 

The signals and points (3 at each) will be controlled by a combination of the MSP 430's and an Arduino Nano for servo based point motors. Not enough PWM on the MSP, nor on the Nano (for one end), and anyway, I already had the MSP chips and firmware written. The Nano will also handle I2C command, and will control the MSP 430 through a Proceed/Halt signal and Aspect-1/2 signal. The Vorsignal aspect is set randomly (its corresponding Hauptsignal is off-stage!) and can have its aspect randomly promoted to a higher proceed aspect to reflect improvement in the road ahead over time.

This is relatively cheap, overkill for sure, but fun to do.
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