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Working Signals...Chapter 2

Postby dkightley » Mon Jan 02, 2017 12:00 am

As a follow on to an old post ( viewtopic.php?f=10&t=124&hilit=working+signals ), I thought I'd document the making of the signals for The Bridge.

To try and get a sense of scale, I really had no choice than to use 0402 size LEDs in the signal head, and to make the signal post as near to scale diameter as possible....as I prototyped in the above referenced thread.

So here goes with the construction of a two aspect stop signal....

The first job I did was to identify the anode and cathode of a red LED, which is marked on the back...ironically, its a shallow "T" with the stem pointing towards the cathode. The identified LED was then pressed into a thick layer of spray-on peelable adhesive on a piece of paper so I could then put it under one of those cheap USB microscopes that have a x1000 magnification so I could see and photograph it.

With it immobile, I was then able to tin the two connector pads.....as shown here:
WIN_20170101_15_46_37_Pro.jpg
WIN_20170101_15_46_37_Pro.jpg (54.18 KiB) Viewed 417 times

We're looking at the back of the LED; the cathode is on the left, and the anode on the right...honest! Ignore the lunar surface...that's the spray adhesive!!

I then scraped the insulation off the end of a piece of 0.1mm magnet wire, tinned it and then soldered it onto the cathode, The wire overhangs as there will be a green LED above it...note its been rotated 90 degrees clockwise! :
WIN_20170101_15_48_20_Pro.jpg
WIN_20170101_15_48_20_Pro.jpg (52.39 KiB) Viewed 417 times


I then soldered another scraped & pre-tinned wire to the anode:
WIN_20170101_15_55_02_Pro.jpg
WIN_20170101_15_55_02_Pro.jpg (53.81 KiB) Viewed 417 times


The second LED was now needed, a green. It was stuck into the adhesive and the pads tinned, then manoeuvred into place so it was above the red LED and the overhanging wire on the red LED soldered to its cathode. A third pre-tinned wire was then soldered to the anode of the green LED. The resultant assembly now looks like this:
WIN_20170101_16_28_03_Pro.jpg
WIN_20170101_16_28_03_Pro.jpg (41.18 KiB) Viewed 417 times

Note up is at the four o'clock position! And both LEDs are facing down.

I checked that both LEDs actually worked by connecting the free ends of the three wires to my multimeter....which conveniently has a LED test output!

To be continued.....
Doug Kightley
Webmaster here and volunteer at the National Tramway Museum http://www.tramway.co.uk
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Re: Working Signals...Chapter 2

Postby dkightley » Mon Jan 02, 2017 12:02 am

One thing I've not mentioned so far....is how horrendously small these LEDs are.

To give an idea, here's the usual photo with a Pound coin: :shock: :shock: :shock:
WIN_20170101_16_23_16_Pro.jpg
WIN_20170101_16_23_16_Pro.jpg (137.44 KiB) Viewed 416 times
Doug Kightley
Webmaster here and volunteer at the National Tramway Museum http://www.tramway.co.uk
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Re: Working Signals...Chapter 2

Postby dkightley » Mon Jan 02, 2017 12:19 am

Continuing the build before any of the delicate soldering falls apart!...

I arranged the assembly on a small piece of thick plastic bag and laid a strip of epoxy resin glue across, ensuring some glue went underneath the LEDS...like this:
WIN_20170101_16_32_48_Pro.jpg
WIN_20170101_16_32_48_Pro.jpg (38.49 KiB) Viewed 413 times

I actually put a bit too much on...but it didn't really matter, as you'll see why in the next photos.

When the epoxy hardened, I folded the wire that was connected to the anode of the green LED over so it was alongside the other two wires. I then threaded all three wires down a piece of 0.5mm OD x 0.3mm ID brass tube, pushing the tube right up to a point where it touched the epoxy. I then laid more epoxy over the top to seal the third wire and the brass tube into the now larger "blob" of epoxy. Note I've spread it out so the area on the plastic sheet is a little larger:
WIN_20170101_17_00_41_Pro.jpg
WIN_20170101_17_00_41_Pro.jpg (37.57 KiB) Viewed 413 times

The end of the tube actually ended up closer to the LEDs as to what is in the photo.

Once the epoxy dried, I trimmed the edges off the now hard spread of epoxy with a scalpel....leaving a signal head shape:
WIN_20170101_20_06_24_Pro.jpg
WIN_20170101_20_06_24_Pro.jpg (51.6 KiB) Viewed 413 times


I then peeled the plastic sheet off the face of the signal head.....and painted the back, sides and lower & upper parts of the face black:
WIN_20170101_20_09_35_Pro.jpg
WIN_20170101_20_09_35_Pro.jpg (48.88 KiB) Viewed 413 times


I've got three red/green and one red only signals to this state....and will get the rest to the same state before moving on. It'll give me chance to decide what to do next!!
Doug Kightley
Webmaster here and volunteer at the National Tramway Museum http://www.tramway.co.uk
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Re: Working Signals...Chapter 2

Postby gbtrains » Mon Jan 02, 2017 7:48 am

Dough
That is great what you have done.
I could not get to solder that small and either ended my fingers getting burnt or soldered over the LED.

I am still trying myself but you can get pico LED lights from this site ( http://www.modeltrainsoftware.com/smd-chip-leds.html ) for about £2.00 odd each and theses come with pre wired. :idea:

I am still working on the three aspect lights.
Will let you know all know if I get better sucess as we need more realism. 8-)

Regards
Graham
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