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Discussion Starter · #1 ·
In a world where it is possible to get cheap dot matrix LED name badges and necklaces, it ought to be possible to find a small enough white 5x7 dot matrix panel about 10mm x 12mm, so that I could produce a colour light signal with a working theatre indicator for the approaches to my station, where 6 platform faces, and one through route, are available.

At the present moment I can't find one. Any ideas anybody?

Colombo
 

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QUOTE (Colombo @ 8 May 2007, 14:11) <{POST_SNAPBACK}>In a world where it is possible to get cheap dot matrix LED name badges and necklaces, it ought to be possible to find a small enough white 5x7 dot matrix panel about 10mm x 12mm, so that I could produce a colour light signal with a working theatre indicator for the approaches to my station, where 6 platform faces, and one through route, are available.

At the present moment I can't find one. Any ideas anybody?

Colombo

Too specialised for the likes of Maplin and Rapid - best bet for UK suppliers would be RS and Farnell. I searched both about 18 months ago - there were a few yellow ones but no white, and the small ones had four or more characters so you'd probably to hide the others somehow. I gave up at that point, but it's a rapidly advancing technology area so worth having another look.
 

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The closest I have managed can be found here on the Forge Europa website. Farnell stock one of their larger displays which is how I located the company. They were asking £16 each for those
! According to the PDF for the 5x7 matrix, the dimensions are 12mm by 18mm which I suspect is a tad large for your requirement. It might be ok for the 7mm fraternity, so don't discard this post


It appears that sizes for 5x7 7 segment displays start at 7.6mm high for the characters and you can get them in white as well as the usual red.

Other design possibilities (and I have no idea if these actually exist) are:-
1) An LCD shutter in front of a white backlight
2) A custom Light Emitting Polymer display or Organic Light Emitting Diode(?) OLED.

If you were really serious about this stuff, you would probably need to talk to a distributor of custom displays. These are the kind of people Bachmann would have dealt with to get the displays for the Dynamis handheld controller - that's assuming that the icons on the handheld are of a fixed design with a simple on / off control rather than the all singing all dancing dot addressable display of the ECoS. The volume and NRE charges are probably prohibitive, but it's fun thinking about it.

David
 

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The idea of an accurate theatre display for 4mm scale has intrigued me for some time.
I can see two possibilities:
1. Use surface-mounted LED chips to build up a display.
1. Use a bunch of fibre optics to carry light up the signal post from a number of separate LEDs under the baseboard. Perhaps the fibres could be terminated in a cast resin block to hold them at the correct spacing from each other.

Roger Amos in the "Complete book of Model Railway Electronics" makes reference to a 7 by 5 matrix which is '19 by 10mm' (it was published in 1990!) and gives the circuitry to enable an F or S to be displayed for a platform departure signal. See Chapter 21, page98-102.

Regards,
John Webb
 

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John, David, Edwin,

Thank you all for your most helpful replies. It seems that we only need a slightly smaller 7 x 5 white dot matrix display and a decoder chip. I don't fancy building the decoding circuit suggested by Roger Amos in his book, which incidently I have had all the time, but I have not read through it properly yet and I had not remembered the chapter.

Just how big/or small do you think the display would have to be for 4mm scale. My guess is about 10mm. Are there scale drawings anywhere of theatre indicators?

I have seen the two articles by Tony Sissons about constructing colour light gantries recently published in MRJ nos. 161 and 171. His route indicating feathers are excellent. Mike Turner has soldered in all the miniature white surface mounted LEDs for him. However I am reluctant to go down that road as the white LED chips are expensive (Express Models have them) and I doubt my soldering skills. Theatre indicators were in use at York in the late 50s and so I would like to have a go at making some of them. I recall that the ones on the platforms displayed an M or an S or an X. No doubt, drivers approaching the station would see an indication of their platform number, but I cannot remember seeing that. Perhaps someone could confirm. By the way, what did X signify?

Colombo
 

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>It seems that we only need a slightly smaller 7 x 5 white dot matrix display and a decoder chip.
I doubt whether smaller sizes will ever become available as there is no need for anything smaller commercially. I mean would you be able to make use of a product with a display that small?

On the possibilities of making something up with SMD parts, one way forward could be to locate a local small scale electronics assembly sub contractor. They specialise in short production runs and rework that is uneconomic to have done in the far east. If you wanted enough of something it might be worth setting up to do a small production run. You may be able to persuade them to do "one offs" for their standard hourly rate.

In my last company we used a small local company who had surface mount equipment, pick and place kit etc, for small runs and prototypes. It's probably beyond the reach of individual modellers but if there was a group who knows?

David
 

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Discussion Starter · #7 ·
David,

I think that we would have to ask someone like Express Models to look into it. I shall put my name down for four.

Do you think that there is a decoder chip for a 7x5 display?

Colombo
 

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A brief search turned up this chip from Maxim. It appears to be ideal for driving 5x7 matrix displays like that white unit I found yesterday. The nice things about this controller are:-

1) The interface is via the I2C bus so you only need two wires from a microprocessor to talk to it. So it would be entirely possible to connect it to a PIC processor which I believe is the processor of choice for DCC....

2) It has a built in font store, so once it has been programmed (at start up), controlling it should be quite simple.

I have a reservation about the size of the chip. The data sheet only lists two package types. The smaller size appears to be 15mm x 10mm which is a little large for mounting on the back of display. One of the four sided leadless packages would be ideal but I expect that's unlikely to happen. It would be great it that could be done as then the connections to the unit from the outside world would be just 4 - power, ground and the I2C. They should easily fit inside a signal post.

This is shaping up to be a nice 7mm project, or maybe S? Still a bit large for 4mm I think.

If one were dead set on using a display like this on a model, maybe they could be used on a modern layout for station destination boards?

I do enjoy looking down these "side alleys"!

David
 

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None of my books give the dimension of a typical Theatre indicator - the latest ones seem to be square, the older more rectangular, the longer axis being vertical. I'll try one or two other sources and report back.

Regards,
John Webb
 

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QUOTE (John Webb @ 9 May 2007, 20:49) <{POST_SNAPBACK}>None of my books give the dimension of a typical Theatre indicator - the latest ones seem to be square, the older more rectangular, the longer axis being vertical. I'll try one or two other sources and report back.

Regards,
John Webb
Just checked the relevant group standard (GK/RT0031 on rgsonline.co.uk) and (unlike main aspects) there is no requirement for size of theatre indicators, just that they should be readable from certain distances. There are however some rules on what characters can be used and how they should appear.
 

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QUOTE (Edwin @ 10 May 2007, 08:55) <{POST_SNAPBACK}>Just checked the relevant group standard (GK/RT0031 on rgsonline.co.uk) and (unlike main aspects) there is no requirement for size of theatre indicators, just that they should be readable from certain distances. There are however some rules on what characters can be used and how they should appear.

Can you give a brief summary of the rules on the characters, please?
Regards,
John Webb
 

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QUOTE (John Webb @ 10 May 2007, 15:58) <{POST_SNAPBACK}>Can you give a brief summary of the rules on the characters, please?
Regards,
John Webb

Easier to paste the actual text:

An alphanumeric route indicator indicates the route to be taken using numbers
or letters (or a combination of numbers and letters). The display shall be
illuminated and the colour of light shall be signal white.
The character font shall approximate to Gill Sans light. Only the following
characters shall be used.

A B C D E F G H K L M N P R S T U W X Y Z
1 2 3 4 5 6 7 8 9 0 [the original is in the appropriate font]

In addition it is permissible for the letters 'O' and 'V' to be used only as part of an
alphabetic indication where the letter has a clear geographic meaning (for
example 'UO' for Up Oldham, to differentiate from 'UR' for Up Rochdale).
Where more than one character is used in an indication, the minimum distance
between the outermost points on adjacent characters shall be 20% of character
height.

More on http://www.rgsonline.co.uk/docushare/dsweb...394/Rt0031a.pdf (section B.10.1.1).

As I previously pointed out, this standard also includes the size and spacing of main signal aspects , so if you have a good enough picture you should be able to scale the theatre size from the main head.
 

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Discussion Starter · #14 ·
Edwin,

Thanks for the lead to the Rail Safety document. That should be very useful for preparing working drawings.

It looks like I can't get a small enough dot matrix display for 4mm yet. So the use of fibre optic strands and a battery of bright white LEDs, together with a diode matrix and a rotary switch is one possibity, if only I can get enough strands up a signal post.

One for the future is a miniature TV screen showing a dot matrix display. Tiny miniature screens are apparently being used in view finders on both digital and video cameras, and in sports and pilots helmets. They also may find uses in correcting vision. Any thoughts in this direction?

Colombo
 

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QUOTE One for the future is a miniature TV screen showing a dot matrix display. Tiny miniature screens are apparently being used in view finders on both digital and video cameras, and in sports and pilots helmets. They also may find uses in correcting vision. Any thoughts in this direction?

Is this the sort of thing you were thinking of?

Personally, I don't think that we will ever see displays at the kind of size we would want for 4mm, it's just too small. The challenge with display technology always seems to be to get it bigger. Maybe we could use the small displays to model 100" plasma screens??

David
 

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I've been sent a copy of the document Edwin refers to in post #13, which gives the dimensions of colour light signals. Using this information and scaling from photos, it would seem that Theatre Indicators are around 2ft by 2ft (600mm by 600mm). So we need a dot matrix about 8mm by 8mm, if anyone can find one that size!

Or if you are modelling Waterloo they seem to use double width ones to give two digits/figures together.

Regards,
John Webb
 

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Discussion Starter · #17 ·
To paraphrase Mrs. Beeton:
"To make a dot matrix display out of fibre optic strands, first catch your strands".

My stock of 0.25mm fibres proved to be too thin and I have had a hunt round for some others. I think 0.5mm diameter would be about right giving a scale 1.5" bulb size. Our local model and electronic shops do not have any unless I am willing to buy an expensive lighting kit and cannibalise it, so I did an internet search.

I have found a site that supplies them: EMA Model Supplies: http://www.ema-models.co.uk/shop/prodpages/page-FOP-20.html

Then I found that Maplins stock 1mm light guides which are 1mm fibres in a plastic sheath making an overall 2mm diameter cable. Too big for a theatre indicator but ideal for a Position Ground Light Switch. Let me explain: the Eckon kit has rather old and dim LEDs and comes in two parts, plus you have to make a third component to receive the LED leads, unless you want to solder wires to each of the 6 leads under the baseboard. I found that the three components difficult to fit together in situ, and so I intend to make a one piece unit that can be slid up through a hole in the baseboard, fixed with a couple of screws and ballasted in. It will be connected in with a 4 pin SIL plug.

As I need about 10 of these it will be a production line job. I shall let you know how I get on.
Meanwhile I shall be looking out for any redundant fibre optic table lamps with 0.5mm fibres.

Colombo
 

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A quick bit of drawing and calculating suggests that even 0.5mm fibres are going to form a bunch some 4mm-5mm in diameter to get all 35 'lamps' of the dot matrix operational. It's possible that if you only want a limited number of characters the number of fibres could be reduced. I'm not too certain either if 'bare' fibres can touch each other without transmitting/leaking light across from one to another, or if they need an outer coating, which will increase their size even more.

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John Webb
 

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>I shall let you know how I get on.
I'm wondering how you are going to get the fibres to turn the sharp corners I imagine are required.

David
 

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I was browsing the Peco Nuremberg report that Gary pointed out and noticed this picture of a new range of Swiss railway signals being manufactured by a Hungarian company. It looks like they have managed to create matrix signs...

David
 
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