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I am using rotary switches to operate colour light signals along with an LED readout at the side of the switch to indicate the setting.

Is there a simple way, eg, some form of resistor in the feed, to give the fade effect of old style signals when changing the aspect?

 

Mike.

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8 hours ago, Junctionmad said:

what do you exactly want to simulate , ie whats the sequence , is it fade out or fade in 

 

As in my era colour lights would be filament type, I think, from what information I have gathered, that they faded out and were pretty much instant coming on.

 

Mike.

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Old-style, say pre-privatisation, colour light signals didn't noticeably fade out (or in), unless there had been a very rare failure one colour and only one colour (but of course two yellows were possible) was lit at any one time. It wasn't unknown to see a signal cleared from red, flash yellow (and even two yellows) for a split second and then go green, much the effect that you might get from turning a rotary switch (although that wasn't why it happened), but just as often they just cleared to the fine aspect.

 

I can think of two examples where things happened more slowly, although no fade effect was involved.

The first involved the old SR-style three light feathers which had to be proved lit for the appropriate route before the aspect would clear from red, but the delay to the aspect change was rarely longer than one second.

The second involved the rather different two-aspect stop signals on the Underground where red indicated, in effect, that the train stop was up (and therefore STOP), while the green indicated that the section ahead was clear. When a signal was cleared, there was a noticeable moment when both aspects were lit because the train stop was still being lowered - as soon as it was the red aspect went out leaving just the green alight, but if there was a train stop fault both aspects remained lit, indicating to the driver that he needed to "trip past", stop to reset the trip and then proceed at caution to the next stop signal.

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35 minutes ago, Junctionmad said:

Is it not the case , that there was never “ fade “ but that the next aspect lit slightly ahead of the aspect extinguishing to ensure there never was a blank aspect , even briefly , displayed 

 

No not intentionally, the feeds to the aspects are (usually) switched simultaneously. Any fade effect is due to the lamp filament taking a fraction of a second to cool down. 

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2 hours ago, bécasse said:

the old SR-style three light feathers which had to be proved lit for the appropriate route before the aspect would clear from red, but the delay to the aspect change was rarely longer than one second.

As far as I know all main signal route and junction indicators had and still have to be so proved, because if they don't light up the driver might be misled into assuming the straight route is set and hit the junction too fast.  With relay interlockings this is normally done by a relay in a trackside cabinet and the delay is barely discernable - it's possible the early SR interlockings had some arrangement that took longer.  However with solid state interlockings (typical in the 1990s) and probably the more recent computer-based interlockings, the central interlocking "decides" that the indicator is proved and sends the instruction to change the aspect.  Due to the timing of the communications this will normally result in a delay of just under a second.  However this is equally true of filament lamps, where some fade is visible, and the LED designs mostly used today, which noticeably "snap" on and off in an instant.  

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The difference is that the old SR-style feathers required all three lamps to be individually proved alight whereas, at that time (pre-mid-1960s) at least, the five light feathers used elsewhere merely needed to be proved to be taking current on the basis that the signal would still carry a clear meaning to the driver even if one of the lamps had failed. That was what I was told at the time by a Wimbledon S&T engineer when I queried the obvious time delay between the feather lighting and the aspect changing - and certainly any delay on other regions' feathers was much less obvious.

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1 hour ago, bécasse said:

The difference is that the old SR-style feathers required all three lamps to be individually proved alight whereas, at that time (pre-mid-1960s) at least, the five light feathers used elsewhere merely needed to be proved to be taking current on the basis that the signal would still carry a clear meaning to the driver even if one of the lamps had failed. That was what I was told at the time by a Wimbledon S&T engineer when I queried the obvious time delay between the feather lighting and the aspect changing - and certainly any delay on other regions' feathers was much less obvious.

I think the five-light version require three lit.  But I'm not sure why proving all three lit should take longer - they would either have one relay for each lamp with a detection circuit requiring all three to be energized, or a single relay on the supply to the lamps in parallel, designed to pick only if there was enough current to indicate all three lamps lit.  The first option probably requires an extra set of relays to close as part of the sequence, the second one doesn't.  But neither takes long enough to explain a second's delay - the actual time would be similar to those signals mentioned above that "flick" through yellow on the way from red to green (not searchlight signals). 

 

There must be some other reason, perhaps slow-acting relays - giving time for the filament to warm up and the current to steady?  

Edited by Edwin_m
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49 minutes ago, Chris White said:

 

I don’t think that’s what the OP is looking for. The circuit in that link will cause the aspect to extinguish shortly after turning on. I think the OP wants the aspect to fade after turning off. Putting a capacitor in parallel will do this, as opposed to in series circuit shown in the link. 

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4 hours ago, Edwin_m said:

However with solid state interlockings (typical in the 1990s) and probably the more recent computer-based interlockings, the central interlocking "decides" that the indicator is proved and sends the instruction to change the aspect.  Due to the timing of the communications this will normally result in a delay of just under a second.  However this is equally true of filament lamps, where some fade is visible, and the LED designs mostly used today, which noticeably "snap" on and off in an instant.  

 

Longer than a second Edwin - a very noticeable delay between the JI and main aspect. (around 3 seconds)

 

 

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This is not strictly simple, needs common anode signal heads, but the component count is still rather small, and there are no processors or fancy digital buses, just one IC (quad operational amplifier) for four LED lamps.

 

Cut the wire leading from (grounding) switch to the LED's curent limiting resistor and connect the circuit points (A) and (B) in between:

 

op_del.gif

 

I drew this in 2006 and had it at Tapiola Parish Model Railway Club's web site's page https://taprk.org/eng/project/semaphore/ for 14 years. After showing this at MERG BBS i was noted that the schematic had power pins of the OpAmp reversed :), This is the fixed one!

 

The idea is that when swiching on a LED, first nothing happens, and then, after about half a second the LED starts to brighten, and is fully lit at one second after being switched on. When switched off, the LED becomes dark within half a second. So, if one switches off one LED and switches on another, the first one will go dark before the second one will start to brghten up, thus giving the illusion of "changing aspect through dark".

 

I wonder if this is the desired action...

 

True, may be done with much less components using a processor following x^3 curve...

 

pekka

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7 hours ago, Junctionmad said:

Is it not the case , that there was never “ fade “ but that the next aspect lit slightly ahead of the aspect extinguishing to ensure there never was a blank aspect , even briefly , displayed 

The new aspect has to be proved lit (by the lamp proving relay) before the previous aspect is extinguished (same goes for a route indicator to be proved lit before the signal will clear to a proceed aspect), it is possible to get a picture with both aspects displayed at the same time although it is difficult for the human eye to notice, although it can notice when a signal is cleared from red to green and it 'runs through' the aspects as stated by Bécasse.

 

Modern systems seem to take ages to 'prove' route indicators and we can have the route indicator and red for several seconds for no good reason whatsoever before we get a proceed aspect.

 

Edit-

Beast has covered the last part brilliantly.

Edited by royaloak
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1 hour ago, beast66606 said:

 

Longer than a second Edwin - a very noticeable delay between the JI and main aspect. (around 3 seconds)

 

 

 I make the single yellow just under 2s after the JI, which is about the maximum if the module allocation is the worst case.  The green takes a bit longer, probably because the signaler/ARS is setting the routes in order.  

 

We had a long debate about this signal a while back I think, when it didn't clear for much longer, concluding there was a fault in the detection circuit.  

Edited by Edwin_m
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Quote

The new aspect has to be proved lit (by the lamp proving relay) before the previous aspect is extinguished

That is not the case at all, for a 2 aspect example the aspects would be controlled by a DR relay, a back (deenergised) contact supplied the red lamp and a front (energised) contact the green lamp. It was not possible for both the be on at the same time. The filament lamp turning on or off does have a brief fade effect as the filament cannot heat or cool down instantly but its very short, you can see the effect on domestic filament lamps if you still have any.

The lamp proving relay would be in series with the lamp current supply and were slugged (slow release) relays that would hold up long enough for the DR to changeover.

The lamp proving relay would affect the aspect of the signal in rear.

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22 hours ago, Titanius Anglesmith said:

I don’t think that’s what the OP is looking for. The circuit in that link will cause the aspect to extinguish shortly after turning on. I think the OP wants the aspect to fade after turning off. Putting a capacitor in parallel will do this, as opposed to in series circuit shown in the link. 

Immediately following the question there was an answer that showed a capacitor in parallel to the feed.

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1 hour ago, Chris White said:

Immediately following the question there was an answer that showed a capacitor in parallel to the feed.

Even that one should have another resistor in series with the battery (or, if the values work out, the capacitor can be put in parallel with the LED "inside" the existing resistor).  This limits the current into the capacitor when power is first applied.  It also gives a bit of a fade up as this happens.  If I remember my physics correctly, multiplying the resistance in ohms by the capacitance in farads (noting that it will be a very small part of a farad!) gives a "time constant" in seconds where the resistance is what is in circuit between the capacitor and the power source for the fade up and between the capacitor and the LED for the fade down.  The fade up/down period will probably be five to ten time constants, although LEDs are a bit fickle so probably best just to try it.  

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I am assuming that the OP wants to 'fade' the actual signals on his layout rather than the LED indicators on the control panel? If so, are the locations of those signals such that the effect will actually be visible anyway for anyone looking at the layout?

 

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Just now, RailWest said:

I am assuming that the OP wants to 'fade' the actual signals on his layout rather than the LED indicators on the control panel? If so, are the locations of those signals such that the effect will actually be visible anyway for anyone looking at the layout?

 

 

You are correct in your assumption and the signals will be visible, or at least as visible as 4mm colour lights can be!, so I was surmising on the practicality of fade, whether it realistically makes a noticeable difference or not.

I thought that there would be a "simple" solution, but if it looks like getting too involved then the idea could well be shelved.

 

Mike.

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