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Processor Control of Lineside Items - The Lineside. - Getting You Started. - Your Model Railway Club
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 Posted: Fri Sep 24th, 2021 11:48 am
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Dave C
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It's been a while since I last posted any updates. So I thought I'd give an update on where we're at at this point in time.

Following on from the (eventual) success of the long running turntable saga that seemed to be never ending, life finally returned to the subject of the automatic signalling project; this is after some decent weather and a number of trips out and away in the caravan (together with numerous other interruptions - otherwise known as illnesses and "life"!). But not before I got round to installing a long forgotten Ground Positioning Signal (for Shunting back into the siding at the small Halt station). It took ages (many days in fact) to find where it had been put for "safe keeping"; and while I was on with thoughts of the GPS, I decided I would also spend a further few days trying to find where I had put the Positioning Signals (two white lights) that will allow a loco to move forward against an otherwise red aspect into a siding area; the Train Room is such an untidy place! After much tearing out what little hair I have left, I finally got them all found - not that I'm going to do anything with the Positioning Signals just yet a-while - but I needed to find them for peace of mind if nothing else; they'll soon be needed in the Terminus as part of this overall signalling project.
A few problems with the Ground Positioning Signal came along (mostly light bleed into an unlit aspect), but finally it was reconfigured and is now in position and wired into the signalling boards - see my post under John Street for more on this signal itself (https://yourmodelrailway.net/view_topic.php?id=14501&forum_id=21&jump_to=304264#p304260).

Returning (at long last) to the Automatic Signalling Project:

First job was to check the signal aspects and this proved simple and easily and quickly checked. Next on the list was to ensure all sensors were wired up and working correctly before I progressed further. One block of four sensors did not fill that criteria; two were fitted but needed adjustment - the other two were just not there at all!

One snag I found was that, now that I am automating the signals somewhat more than I had previously thought, which also included occupancy detection (of sorts), and a need to detect the entire length of a train and not just the loco (which already has a small piece of silver foil stuck under each belly, this being easily detected by the in-track sensors), the underbelly of coaches and trucks were not reflective enough to be detected by these sensors and I didn't want to have each and every coach and truck with silver strips of foil stuck underneath. This has meant having to replace each in-track sensor with an across-the-track sensor and to effectively hide them from view, blending into the scenery, etc. Not so easy when two of the sensors are on a double-track part of the layout. Hence a few low lying bushes have suddenly sprung up between the two running tracks to hide the infra red emitters; the sensors are hidden elsewhere not too far removed from the track side either in more bushes or inside buildings. The line of detection needed to be at an angle to be high enough to be blocked by the coach/truck body (not the through wheels) and at such an angle along the track so as not to see the inter-coach coupling gaps.

For those with figures and more detail on your minds:
with the RPR-220 emitter-sensor pair buried into the tracks, the voltage swing between sensing a coach/truck or nothing was around 0.5v with a +5v supply and a 470k resistor in the receiver collector circuit (refer back to https://yourmodelrailway.net/view_topic.php?id=16438&forum_id=7&page=1#p296757 which gives the circuit details). And a 0.5v voltage swing was certainly not enough to be considered stable enough for detection by the LM339. Back to the drawing board then.

The idea of using across-the-track sensors was again looked at but with a gap between the emitter and receiver (on one particular sensor position) of around 10inches (255mm) the sensitivity of the circuit was a little lacking. I tried pushing up the emitter power, perhaps beyond its undisclosed rated value, to 70mA. This made a slight difference in the sensed voltages, but not enough to be overly comfortable. So the emitter current was dropped back to 35mA (I think a normal maximum value would be 50mA) and the sensitivity of the receiver checked with differing collector resistor values. At 100k (more normal for a +5v supply) there was little difference between states; at 470k things started to look a little better and with careful alignment I could get a difference of 1.25v between train and no train on the test bench. I then tried increasing the resistor to 1M and at this point I started to get the inevitable 'leakage' current through the sensor and possibly also the LM339, but the train-in-position voltage dropped to 2.9v - giving a nice and acceptable 1.5v difference - all this on a +5v supply. I eventually settled for a 680k resistor which gave me, when emitter and sensor were fitted and glued into place, 4.52v blocked and 3.37v clear path giving a difference of 1.15v over a distance of 9.75inches (250mm). On the test bench I was able to get a usable voltage difference over a 15inch (380mm) gap, but the difference was starting to become minimal.

So that's been fun! This is what this hobby is all about for me - experimentation to get an end result that suit the situation.

So now I have to go back to the software side of the project and make a few changes in the program to reflect the change from in-track sensors - where I had need to add additional code to compensate for the gaps between coaches (the couplings). The only in-track sensor is now only going to be "looked at" when a train is reversing into the Halt siding. Overall, it should make the program a little faster.

That's it for today - hopefully I may get out for a breath of fresh air and stretch the legs this afternoon and then (just maybe) I can get back into the train room and get the new sensors fitted onto the layout.

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 Posted: Fri Sep 24th, 2021 01:48 pm
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Passed Driver
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Hi Dave C. Reading your thread reminds me of one of my ideas, after years of lighting up the night sky, when “ Motoring over the end of the third rail while working on London Underground , followed by the Arc. The modus operandi that I chose involved a magnet under the motor bogie, but now I cannot see that there is enough space between the track and underside of the bogie for a neodymium magnet, as 2mm is the thinnest one I have seen advertised. Best wishes Kevin



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 Posted: Fri Sep 24th, 2021 08:03 pm
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Dave C
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Thanks Kevin

I recall the arc of the LU trains many moons ago when I lived/worked down that way. And also on the Southern 2-BIL,2 -HAL, 4-LAV, etc. units when I lived not 25 yards from the main south coast line (not that I knew the nomenclature at that time - they were just trains that rattled the windows to me at age 5 or so). I'm sure the drivers did the arcing on purpose!

You mention the small magnets under your locos. On my first layout I used that sort of thing riding over a reed relay across a couple of sleepers just beyond a signal. It worked quite well. Everything then was done using nothing much more than diodes and suitable voltages applied. But that was only used to trigger a signal from green to red - I can't recall how it went back to green again - probably using more diodes further down the track when the next signal went from green to red.

And as the track on this layout was already laid and cutting the rails to allow for current detection was not feasible there had to be another way of achieving the same result - detecting the presence of a train or part of a train on a given section of track and to light up an LED on a track diagram to give a visible indication should the train be in a section of track hidden from view.

But these days I'm wanting to use microprocessors which will not just change signal aspects but also simulate track occupancy. Namely, so long as a loco, coach or truck is present in a section then the section before that signal will not become "clear" and the previous signal will remain at red. A sensor is placed across the track so that once blocked by a loco it immediately trips the signal (signal B) just passed to red and puts that section as occupied. So long as that sensor remains blocked by the remainder of the train the section just being left remains "occupied" and the previous signal (signal A) remains at red. Once the final coach has cleared the sensor, that is when that previous signal (signal A) is allowed to go to a yellow aspect (in the case of a 3-aspect signal). It is, I guess, a software version of (in the real world of full sized trains) the more modern track circuit where a wheel-set/bogie makes a "circuit" across the two rails and a small current is drawn between one rail and the other and it's this loss of the voltage on one rail which is in turn used to indicate something is on the track in that section of track, i.e. section blocked.

This was never thought about when I first started this layout. The initial idea being to simply change signal aspects. Then the problem came about of the in-track sensors not being able to properly detect the presence of a coach or truck for the track occupancy. New sensors, update the software.

This is how the layout has developed over time. Start with the basic and then think about what might come next - and then solve the problems caused. If I had a plan....... how many times have I heard that?



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 Posted: Sat Sep 25th, 2021 09:30 am
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Passed Driver
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Hi Dave C.  Thank you for your reply. My idea is to mount the “Reed switch “ under the baseboard with the LED on the surface. The idea works well with a non motorised bogie or a wagon etc. But it has to be on the lead/tail end,As for signal control, I like your idea but it isn’t for my Plank. The so-called professional dealer seen at the long missed model Railway shows, where I had seen various ideas that didn’t appeal to me, but two rail models cannot follow the true system, meaning the two running rails only carry the track circuits which isn’t possible with modern models. As usual I am running out of steam.  Best wishes Kevin 



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 Posted: Sat Sep 25th, 2021 10:12 am
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Passed Driver
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Hi Dave C.     More info? I wasn’t  old enough to have a Tin Plate three rail system, but, I did see a circle of “ O “ gauge track with tin plate trains running around, arcing as well, I don’t know if that third rail could allow track occupancy or track circuitry. Best wishes Kevin 



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 Posted: Sat Oct 30th, 2021 01:18 pm
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Dave C
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This automatic signalling project just seems to be never ending - there's always something getting in the way of getting it completed.

Only the other week I bought a new loco (as a treat to myself as it fitted in very nicely with the timescale of the layout). Only problem was that it didn't like one set of trailing points and kept derailing. The main issue was this set of points is buried under the main terminus throat and far from easy to get at. There's more to read on this at https://yourmodelrailway.net/view_topic.php?id=14501&forum_id=21&jump_to=305347#p305335

So that took a couple of weeks to sort out.

Then there was an errant couple of sensors I thought had been installed - but no. And that turned out to be a can of worms, so-to-speak. And it turned out more difficult than I had expected. The sensor, a 2-leg device, looking like an ordinary LED but darker, you would expect to connect it the same as an ordinary LED - long lead to positive/supply and short lead to ground. No! Whoever thought it would be a good idea to swap it round - long lead to ground, short to positive.......

No wonder it wouldn't work!

And then I thought that I would like to be able to switch off at the end of a running session (or in the case of a power fail) without the need to store everything back in sidings or in the terminus and to be able to pick up exactly from where I left it, occupied sections and all. Such is the problem with software-derived signalling and occupancy detection as opposed to "current detection". Everything normally gets lost at power off.

So that's meant another look at the programming - hoping in the process I'm not slowing things down too much by adding in these extra (write to eeprom) commands.

Surely this project can't be far off completion now, or maybe.....



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 Posted: Mon Nov 1st, 2021 11:17 am
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The more I read about your journey Dave, the more I realise how much fun one could have from the old Hornby "O" Gauge clockwork trainset .................... :roll:

I'm assuming you know what you're doing because I got lost when you mentioned "breadboard" and didn't follow up with the type of flour you'd used ................... :cheers

It does however, seem that you're making steady progress so onwards and upwards Sir !! :thumbs



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