Buffer stop with switch to detect contact

[melmerby]

Hi all

 

I would like to build some buffer stops incorporating a switch to detect when a loco/coach etc. has made contact but the switch needs to be very light in operation on not obvious to the eye

They should look something like these at the traverser in Moor St when finished:

 

http://www.warwickshirerailways.com/gwr/gwrms1223.htm

 

They are partly rail built with a substantial plank, which is up against the plarform end.

 

http://www.warwickshirerailways.com/gwr/gwrms1735.htm

 

I aim to make them look like as in these in the pictures and they are at the end of a traverser in my station.

I might even have a man with a controller

 

Any suggestions?

 

Cheers

 

keith

Edited January 15, 2018 by melmerby

[John ks]

Keith

Something like this might work

 

 

I have extended the platform above the buffer beam to hide the gap between the beam & platform support wall

 

OR if you don't mind the gap then use the version on the RHS

 

I would fit 3 guide pins(red) to the buffer beam & use the middle one to activate the micro switch

 

Some experimentation with the micro switch will be necessary 

 

John

[DCB]

Edit]    The buffer centre line height is higher than the max platform height, I can't remember the exact dimensions off hand, so John's concept is flawed  The buffer stop must project above the platform or it looks very wrong

I think you will have trouble making it work freely enough so that the switch makes contact with a light kiss yet springs back when the vehicle is removed.    Also couplings are in the way for using buffers and also so many modellers don't have any standardisation in buffer heights that its not feasible. People used to spring load a piece of track so if a loco ran on to it a switch made contact and a light came on but with today's featherweight stock that won't work

Edited June 5, 2019 by DavidCBroad

[melmerby]

Keith

Something like this might work

 

buffer.jpg

 

I have extended the platform above the buffer beam to hide the gap between the beam & platform support wall

 

OR if you don't mind the gap then use the version on the RHS

 

I would fit 3 guide pins(red) to the buffer beam & use the middle one to activate the micro switch

 

Some experimentation with the micro switch will be necessary 

 

John

That looks a possibility.

I could mount the switch horizontally between the platform surface and baseboard (there is 12mm clearance)

 

Cheers

 

Keith

[Oldddudders]

Kissing the bufferstops is frowned upon in most quarters. Why not use some optronics in the 4’ way just short of the stops?

[melmerby]

Kissing the bufferstops is frowned upon in most quarters. Why not use some optronics in the 4’ way just short of the stops?

That is another possiblity but trying to disguise them as something else is the problem

I do have some IR devices including a double sided emitter which if mounted at buffer height in the 6 foot and receivers either side could detect the presence of a loco/vehicle

 

Keith

[Grovenor]

Kissing the bufferstops is frowned upon in most quarters. Why not use some optronics in the 4’ way just short of the stops?

In this case the 4ft way will be tricky as the traverser is there, but it should be possible to have an IR detector looking out from under the platform edge.

Regards

[73c]

How about a Photo optic device. Detecting light/dark ( the loco over it ) some of these 99p items on the bay have the sensor on legs which could be carefully bent to help reduce clearance needed.

[Reorte]

If hiding the device is a problem how about a magnetic approach? Hidden magnetically operated switch near the buffer stops and a magnet on the bottom of the stock you want to stop there. It sounds partially like operating a magnetic coupler in reverse.

[cliff park]

The reeds from a reed switch are good for this. Can be laid across the track between the sleepers and hidden with a (thin) layer of ballast. The important thing is that the operating magnet is parallel to the reed, they will not operate if at right angles.

[melmerby]

If hiding the device is a problem how about a magnetic approach? Hidden magnetically operated switch near the buffer stops and a magnet on the bottom of the stock you want to stop there. It sounds partially like operating a magnetic coupler in reverse.

Too many locos plus other items.

It really needs to be independent of the rolling stock.

Thanks for the suggestion though.

 

I think opto is the way forward

 

Cheers

 

Keith

[melmerby]

There is a small amount of room at the end of the traverser before the buffer stop (about 35mm) so I wondered about a small emitter,  in the 4ft just after the traverser, and a receiver above disguised as something else (lamp?)

 

This could be triggered immediately any overhang reached it.

 

Keith

[73c]

One of these would detect the shadow of a loco sat above it.

 

https://www.ebay.co.uk/itm/LM393-Optical-Sensitive-LDR-Light-Detection-Photosensitive-Sensor-Module/161894622735?hash=item25b1abe60f:g:lo4AAOSw7FRWUUFL

 

There are cheaper ones but depends on how long you want to wait for it.

[melmerby]

I decided to go for IR detection using an IR LED & IR phototransistor.

 

I have purchased some suitable devices.

These will be mounted at buffer height and detect the buffers breaking the beam, which I have tested in principle.

 

All I need to do is disguise the devices as some sort of railway structure  

They are approx 5mm x 5mm x 2mm

 

Any suggestions for things between the tracks in a terminus station sticking up about 3' 6"? (1930s or so)

I can mount some on the platforms disguised as trunks or boxes left there

 

Cheers

 

Keith

[Brian]

I use IR detection, but fitted between two sleepers and pointing upwards. Therefore the two items are virtually invisible! The upward IR beam is reflected back by whatever passes over it, back down to the receiver IR LED.  

Heathcote Electronics and BlockSignalling to name two suppliers who make ready made IR units 

http://www.heathcote-electronics.co.uk/irdot1.html

http://www.blocksignalling.co.uk/index.php/infra-red-train-detector-bod2

 

Edit to add second URL

Edited February 3, 2018 by Brian

[CarriageShed]

The Blocksignalling url has changed since 2018, but that's precisely what I was looking at myself - and it's what brought me here via a search:
http://www.blocksignalling.co.uk/index.php/train-detector-with-relay-bod2-rly

 

I'd like to slow a slow train to a stop in front of the buffers in a terminus. The trains will be half hidden behind a station building so I won't be able to see the crashing-into-the-buffers moment myself. The trouble is I am to electrics what Donald Trump is to civility (ie. a near-complete stranger), so the solution has to be a very simple one.

 

Did the OP ever produce a working solution to the problem?

[CarriageShed]

Hmm... looking at the Heathcote option it suggests (to my limited understanding) that a light on the control panel could come on once the train reaches the sensor:
http://www.heathcote-electronics.co.uk/irdot1.html

 

If the train is travelling at a slow buffer-approach speed and the light comes on, the operator would know that it's time to ease to a stop, manually, but reliably. Am I right in that?

[melmerby]

Sorry Folks.

I've just noticed that I posted this in the non DCC section, when in fact it is part of a DCC setup.

The idea was that the detection should work as the stop marker in a detected DCC block, it would be operating automatically.

 

I have made the idea work using IR opto emitters/detectors but not yet fitted them to the layout, however I can actually get the trains to stop close to the buffers automatically with settings in the DCC program!

 

[ColinK]

I used the Heathcote device which lit a led when a vehicle reached a certain point, worked perfectly.

[melmerby]

I've decided to try VL6180X ToF devices connected to an Arduino.

Doing it this way means you can measure distance directly. Aim it at the locos buffer beam.

Then you can set a trigger at the distance required so that the loco stops at 20mm, 30mm  or whatever

The device will be behind a buffer stop, below the plank.

[AMJ]

Depending upon the settings of your decoders many can be set up to stop on seeing a DC section of track.  How about setting a few inches switchable between DC and DCC but optical solution will be best if you are reversing rolling stock towards the buffers.

[melmerby]

I have just tried a lash up test circuit using the VL6180X module and it's quite impressive as I can get a detection accuracy of about +/- 2mm at 50mm using a 3 plank wagon as target.

I now need to try it with something that has just the buffer beam proud.

[melmerby]

Seems to the job, just as I require but I have hit a snag. I want to use several simultaneously.

The VL6180X (and similar devices) use the I2C data bus to connect to the Arduino, RPi etc.

Each item on an I2C bus has a separate bus address in the format 0x28 etc, so if you have several items you can assign a different address to each and they don't clash.

The  VL6180X has a programmable address with a choice of several addresses which can be easily programmed.

But this "new" address is not stored in non volatile memory and each time you power up the item you have to re-do it!

What a bonkers bit of design!

 

[RobjUK]

1 hour ago, melmerby said:

The  VL6180X has a programmable address with a choice of several addresses which can be easily programmed.

But this "new" address is not stored in non volatile memory and each time you power up the item you have to re-do it!

What a bonkers bit of design!

 

From the data sheet, it looks like you can use the CE (GPIO0) input to selectively power on the sensors, so each can have its address set before enabling the next one.

 

You would need a few extra I/O lines - or a shift register and pins for clock & reset, to step through the enables to any number of sensors.

 

Edit - note that you need to wait more than a millisecond after setting the enable high, before trying to access the sensor or reconfigure it.

 

Edited September 27, 2019 by RobjUK

[melmerby]

14 minutes ago, RobjUK said:

 

From the data sheet, it looks like you can use the CE (GPIO0) input to selectively power on the sensors, so each can have its address set before enabling the next one.

 

You would need a few extra I/O lines - or a shift register and pins for clock & reset, to step through the enables to any number of sensors.

 

Edit - note that you need to wait more than a millisecond after setting the enable high, before trying to access the sensor or reconfigure it.

 

looks like the solution is the TCA 9548A I2C multiplexer, which is sold as an Arduino accessory.

It can mutiplex 8 x I2C busses to 1

Edited September 27, 2019 by melmerby