Are you using different resistors values with the red and green side? Because you typically need a larger value resistor for red, equal current to both sides generally does not equal equal brightness, both due to the different chemistry and the perception of the human eye.
Dick Bronson has probably the best THREE color LEDs - he had them made with specific colors to match proper railroad red, green, and yellow.
Honestly I don't see the hot spot - I see a small section at the very top that is darker, probably because it is in the shadow of the green part of the LED. Green is probably similar, witht he slightly darker spot 180 degrees opposite that for when red is lit - it just may be less noticeable because the green is more diffuse than the red in appearance. Once enclosed in a signal head and facing the track so it's not directly end on visible I can't image you even see that. But try a reduced current for the red side - maybe 1ma for red and 2ma for green.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
RR_MelDo you have a link to Dick Bronson’s site? That sounds like the best solution.
Googling around I found this, very last product is an led. Bronson wrote all the articles on another page of this website.
http://www.rr-cirkits.com/description/index.html
Henry
COB Potomac & Northern
Shenandoah Valley
I agree with Randy about the need for different resistors for the different colors. I built an Oregon Rail Supply signal bridge, but when it came time for the lights I couldn't get them right until I realized that they needed to be in series, not parallel, because the internal resistance of the LEDs themselves would not let current flow through both red and green lights in a parallel circuit.
It takes an iron man to play with a toy iron horse.
Maybe if you used some fairly fine sandpaper to rough up LED case a bit? I assume this is a diffused one and not a water clear. The water clear ones I've seen have very definitely visible spots right at the actual emitting junction. That's probably the difference with modern ones - the point contact is more of a point than an area, so the light truly is coming from more of a point. Improved manufacturing techniques do not always equal a better product.
rrinker Maybe if you used some fairly fine sandpaper to rough up LED case a bit? . . . . Improved manufacturing techniques do not always equal a better product. --Randy
Maybe if you used some fairly fine sandpaper to rough up LED case a bit? . . . . Improved manufacturing techniques do not always equal a better product.
Lucky guess, diffusing it more to hide the spot.
Comparing the pictures, the hot spot was not visible in either (I think direct view is just way too much for the camera to resolve without some even more extreme settings), however in the new picture, the red is more continuous without the flat spot at one point like the first pic.
I'm no photography expert either, all I know is that for any chance of the camera even showing what you see with the naked eye is going to need to be darkened a whole lot more. If the hot spot is noticeably brighter than the rest of the glow in the diffused casing, then the light level has to be reduced so much that the regular glow is pretty much blocked out, allowing only the bright spot to be picked up by the camera sensor. Smallest aperature, fastest speed, and lots of filters, I guess - anything to reduce the amount of light getting through. Probably beyond the basics which is where I run out of ideas. This is a pretty specialized thing to get a photo of something so specific because you are trying to photograph a light source itself, rather than a subject illuminated by a light source. Like trying to take a picture of the sun - hey, you wouldn't happen to have a welding helmet, do you? That might be a dark enough filter. But the plain type, not those fancy new auto-dark ones that go clear so you don't have to lift the helmet and then automatically darken when you strike the arc. The LED probably wouldn't trigger the darkening. If you're still interested in trying to picture it. I have a ton of cheap bi-color LEDs that came in various kits, I'm going to hook a few up and see if they have the same issue.
BTW did I read that right, you have the bi-color LED with a dedicated yellow LED stuck behind it to make the yellow? How does that fit in the signal housing?
rrinker BTW did I read that right, you have the bi-color LED with a dedicated yellow LED stuck behind it to make the yellow? How does that fit in the signal housing? --Randy
Well that's certainly an interesting DIY way to get 3 colors. Thankfully I don;t need to do that sort of thing (I think I'd spend the money and get Dick Bronson's tri-color LEDs if I did), since my prototype used Type G 3 light signals, so I need discrete sets of 3 LEDs, never 2 or 3 colors in the same hole. So long as I don;t screw it up and put the wrong color LED in the wrong position.
I dumped a whole bag of LEDs (some day I will get ALL my parts sorted out into the small drawers I have) and every single one was a water clear, not a diffused one to be found. ANd of the first half dozen I tried, all were a single color (very obvious because the die is visible through the water clear case). As to which is what color - only way to tell is poer them up. With very low current (I set my power supply to current limit at 1ma), a green one looked like, well, a blob of green light - souldn;t really see the point of emission, the whole thing lit up green. But a red one - if viewed straight on, it;s a tiny point of red, with a slight bit of halow around it if not truly perpendicular to the eye. From more of an angle, it's a solid red blob. So I'm guessing the hot spot appearance has to do with the way the point contact is made - red is a natural color, it;s just chemistry, but some other colors are really UV lighting a phosphor - except green normally isn't, green is a discrete color like red, and should have the same issue. White and some blue shouldn;t do that, because they rely on the phosphor, although there still may be a hot spot with such LEDs, it would be in the UV and not visible. That's why I had the idea of making the diffused ones more diffuse with sandpaper. The water clear ones are like magnifiers, so the point of light is very obvious. It seemed weird that this would happen in a diffused package, but my thought was that it wasn't diffusing enough. Glad it worked out. I should see what happens if I rough up one of my water clear ones.
Hi Mel,
Your 'Mel' signals have inspired me to resurect a very old scratchbuilding project. I started to make my own searchlight signals quite some time ago, but for various reasons I dropped it. I have the signal heads already made and I have all the ladders, platforms and signal boxes to finish the project. Thanks for the kick in the bum!
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
You could probably run the entire layout off a single Arduino Mega - if you used something like the Microchip MCP23x17 port expanders. They're about $2 each, and give 16 bits of inport or output, driven with either SPI or I2C, and you can but up to 8 of them on each SPI or I2C line. Unlike shoft registers they are directly addressable, so you don't have signals flashing, or going blank while all the new data is shifted in. Like most things, there are libraries for these, so it's easy to write data to them, or read them - a pair set up for input would give you connections for 32 detectors with just 4 pins of the Arduino used. Another 4 pins and you could have up to 128 LEDs driven. Outputs of the 23x17 are low current, ok for LEDs, but you could do the same with your lighting controller and have the 23x17 outputs drive the high current drivers to control light bulbs. Heck, I think with a bunch of 23x17s and the drivers, one Mega could run both the signals AND your structure lighting. There's enough code space, enough pins to run multiple I2C or SPI buses, and it should be plenty fast enough. I'm using those 23x17s on my psuedo-CMRI control nodes, and the cpNode from MRCS uses them for their IO expanders.
If it helps anything, in a previous life I addressed the issues with older bicolor LEDs driven to produce a range of orange/yellow in AC (the specific application being safety repeater boards for nuclear powerplants in ITU gr.oup R10)
The "AC" drive to the LED has to be asymmetrical to control both the apparent color and brightness issues in 'yellow'. We did this in time domain in order to retain perceived isoluminance when either diode core was lighted with straight DC through appropriate resistance. Doing this at the desirable high frequency is much easier and cheaper than it used to be!
The LED face, whether domed or lensed, needs to be made 'diffusing' after the manner of an averaging photo lightmeter dome. As I recall, something like Testor's Dullcote applied over solvent etch of the plastic face of the diode encapsulation would serve; this might be easier and certainly less time-consuming than trying to fine-sand especially once a signal head had been assembled.
rrinker You could probably run the entire layout off a single Arduino Mega - if you used something like the Microchip MCP23x17 port expanders. --Randy
You could probably run the entire layout off a single Arduino Mega - if you used something like the Microchip MCP23x17 port expanders.
Somewhere I know it mentioend what exactly colors Dick Bronson used in his, but a quick look at the page didn;t find that info - if you had to order the LEDs anyway, might as well get a correct railroad green and amber
My only fear is that with them stacked like that, it will be readily apparant which color is on by the physical location within the lens, unless it REALLy diffuses the light.
rrinker Somewhere I know it mentioend what exactly colors Dick Bronson used in his, but a quick look at the page didn;t find that info - if you had to order the LEDs anyway, might as well get a correct railroad green and amber My only fear is that with them stacked like that, it will be readily apparant which color is on by the physical location within the lens, unless it REALLy diffuses the light. --Randy
I'm not sure I'd even want to attempt the 0603's - my hands are quite steady but I really can only see out of one eye myself, only mine's from glaucoma and not fixable. Those 3D things where you sort of go cross-eyed to see them, or the old stereoscope style where you put a barrier doen the center and have two slightly different images for each eye - now lost on me. I used to be good at those crazy image ones, too. Magnifiers or not, my current soldering method has me soldering inches from my nose, and the depth perception is off so trying to hit the right spot is very difficult.
I'm lucky in that my prototype doesn;t require all sorts of lights in my locos, just a headlight and a rear light if a diesel. Most of the time a 3mm is just fine. I am NOT looking forward to building all my signals, though since they are Tpye G I can probably make do with 3mm or maybe the slightly smaller ones (I think you can still get 2mm as a through hole type). Or I will be forced to use only pre-wired SMD types.
It's not just the amber - the RR green is more of a sea green, compared to standard green LEDs. Of course, since you have a bunch already made using plain green LEDs, no point in making some different at this point, it would stand out and probably not in a good way.
I recently made an inquiry to a eBay vendor (China) about the N scale signal lights he was selling. I was asking about using bi-color. His response indicated his LED(individual red and green) were 2mm and they were the bulb type....not SMD. Don't know where to get the 2mm but eBay seem to sells everything now
Paul D
N scale Washita and Santa Fe RailroadSouthern Oklahoma circa late 70's
Sure is, and I'm not even that old yet (52). Your vision should end up quite decent - my Mom had cataract surgery on both her eyes and at 80 was seeing better without glasses than I do with mine - I forget my exact number but my glasses are quite thick, and I think I MIGHT be able to see the large giant E on the eye chart without glasses - clear vision is about 5 inches from my nose. Best part is - because of the shunts installed in my eyes to control the glaucoma (left eye is still good, no damage, and has been controlled, right eye is already damaged, and inists on being stubborn - I've had FOUR surgeries on it, 2 different implants and 2 laser surgeries, and even with medication, it remains stubbornly high, though fasr better than when I first went in) there is pretty much a 100% chance i will develop cataracts. So I have that to look forward to now as well. Good news is besides that, my knees are my only other real problem so far. Which is why I bought a single story house
Anyway, i think we had the eye problem thread a whiel ago. I know I;ve seen 2mm LEDs at some of the big suppliers, so I'm sure there are low cost versions on eBay and from Chinese suppliers. I need to get measurements to see what size is needed - there is a Type G signal head in the RCT&HS museum collection that I have access to to see just what diameter each of the lenses is. There are others at the RR Museum of PA, but I think they might at least look at me funny if I tried to reach up and get a measurement.
Or cheat and buy already built up ones - Atlas and NJI have them - but where's the fun in that? Of course, vacation time is nearly up and I made exactly 0 progress on finalizing my turnout controller and getting it to a point where I can have a PCB made. I am forcing myself to get the basement cleared out and new walls up this spring, if it kills me.
Edit: quick check of eBay, there are both 2mm and 1.8mm LEDs available. Most of them have a larger base part and the tops are turned to be 2mm or 1.8mm in diameter. Which is almost perfect for a signal, the blocky back can be painted over and made to look like the bulb housing.