I know, I asking a lot of question but I'm working at learning. My decoder output is 12V. measured. It takes 3V of battery power to light the LED. 1.5 V won't do it.A 1k resister in line won't light it. 2 =1K resisters in parallel won't light the led.What am I missing? The decoder gives the proper response for other commands.
Thanks in advance.
Lee
I use 1,000 ohm resistors to light led's. you must observe polarity with the leds. Try reversing the leads. does the led light when you put it across the rails with the resistor in series?. Using less than 600-800 ohms may make the led too bright.
Which wires are you connecting? If it's blue-and-white, then the engine needs to be in forward. For blue-and-yellow, it needs to be in reverse, assuming you haven't made any changes to CVs to re-map the output functions. Also, F0 needs to be on. (Sorry if these are silly questions, but some people coming over from DC have had exactly this problem - there's no On/Off switch for headlights in DC.)
If you're using blue-and-white, have you tried yellow-and-white? You may have a bad function on the decoder.
It takes an iron man to play with a toy iron horse.
I get the color code for the engine wiring from the light board that I took out. This allows me to use a battery to light the LED. The NMRA color code tells the polarity of the decoder out put. Unless I'm missing something EDIT I measured the decoder out put.
I'll rethink it.
The 1.5 volt connection of light board decoders are Only for 1.5 volt bulbs.
For 12 volts DC, I use 750 ohm resistors for LED's which allows about 15ma current.
A 1,000 ohm resistor allows about 10ma current. A little difference in light intensity.
Polarity has to be observed with LED's.
Lighting link below. Store the link in Favorites.
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Polarity is probably backwards, a single 1K should be just right. Two 1Ks in parallel is 500 ohms, probably too low - so it's probably good it was backwards.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
You mentioned testing the LED with a battery. Does it still work when you do that? A battery can put out a lot of current, so if you didn't use a resistor you may have "flash-tested" the LED, in which case it could now be a Darkness Emitting Diode, or DED.
Thanks Guys you made me think. I had measured the output of the decoder but I went by the plus and minus signs of the decoder. This Bachmann OE decoder puts out positive on the blue wire negative on the white.I thought NMRA code was reverse.
There's joy in Mudville everything works.
Jeff But it's a dry heat!
Hey JeffWhat threw me, to an old vacuum tube tech, common is negative and even in household AC I think of common as ground. You don't put a switch in the common side. These LEDs are a new wrinkle for me. I'm learning.
Have a good day.
Thanks for letting us know about the happy outcome.
I love it when a plan comes together.
yankee flyer Hey JeffWhat threw me, to an old vacuum tube tech, common is negative and even in household AC I think of common as ground. You don't put a switch in the common side. These LEDs are a new wrinkle for me. I'm learning.Have a good day.Lee
I agree with you that it seems backwards. I usually don't pay attention to the polarity of the LED. I use 1K resistor on the LED. I attach it to wires and if it doesn't light I reverse and try again. While some people may think it's crude and may be more work, it has worked for me. Also the LED's I have for headlights I got out of Christmas lights and I am not sure that the leads are correct.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
The handy thing about using the high as the common is that by doing that you can wire more than one open collector driver to the other side, and drive the led from more than one function output. It's not just to confuse people!
A really good online LED resistor calculator can be found here:
LED resistor calculator
Since you mention it takes 3 volts to light your LED and your output voltage is only 12 volts, that 1K resistor is too much resistance. According to the calculator you need around a 470 ohm 1/2 watt resistor. So your LEDs may work with a 1K resistor, but they will not be as bright as they can...that is if 3 volts really is the max voltage they can run at. What are the manufacturers specs on your LEDs for voltage?
Are you using white LEDs? They typically need 3 volts. Most other colors are lower voltage.
Oh, one last point. Typically the value to place in the last part of that online calculator is 20. Most LEDs are around 20 milliamps.
I recently installed some golden white 3mm LEDs in two G scale locomotive headlights. My power source is 16 volts. Using a 680 ohm resistor is what the calculator suggested. The LEDs work beautifully and are nice and bright. Using mini flashlight reflectors really adds to the light output and focus as well. A neat feature you can use with G scale trains.
Matt from Anaheim, CA and Bayfield, COClick Here for my model train photo website
I'll keep that LED calculator site in my book for the future use. the 1K resister seems about right as far as brightness.I had to use two "C" cell batteries stacked, maybe one 1.5V "C" cell didn't have enough oomph to light the LEDs.
Thanks
Once again, misreading the LED specifications. 20ma is the MAXIMUM. You do not want to run at the maximum for anything. Plus most white-type LEDs are BLINDING, using a 1K resistor gets them about 9ma dn they are still plenty bright, especiallyon locos where the LED is directly visible, or simply behind a clear lens - my Stewart AS-16's with 1K resistors are really kind of too bright still, whereas with more 'light pipe' to pass through, the 1K works great for a P2K Geep.