Is it possible to use a DCC chip to power/control one or more LEDs in a DC loco with constant brightness when the loco is running?
The objective would be to have constant brightness only whilst the DC loco is moving, and the loco itself is powered using DC via the tracks.
I have used different types of integrated circuits to do this, but they are bulky, especially when you start adding resistors.
Just wondering if I have been missing a trick! I suspect the answer is "no".
The answer is no. I'm pretty sure.
However the 'Minitrains' headlamps are almost constant brightness when using their PWM controller, which supplies 12volt pulses. A diode, resistor and LED, all of which are available as surface mount, would suffice.
Funny you mentioned a PWM controller - I have just ordered one!
Egger-bahn managed to do this in their blue electric loco back in the 1960
Hello Brian.
DCC chips (which I have never used, and have no knowledge of) amaze me because of their ability to control the power supply to LEDs (let alone the motor, of course) with such incredibly small components.
Even a small bridge-rectifier (to enable LEDs to light up when the train is running in either direction) is bigger than a DCC chip. Bridge-rectifiers drop precious voltage too, and you still have to use some kind of (relatively huge) IC component to regulate the power-supply to the LEDs.
Hence my question: I was just wondering if there is some way to take advantage of (hack, in computer-speak) the miniaturised components on a DCC chip, whilst running everything off DC.
I do get a constant LED light in either direction in a Chris Ward railcar using the Digitrax DZ125 decoder on DC. It also pulls away very smoothly at low speed.
I put all the instructions for installing these decoders in a OO9 News article last year.
Jim, this sounds very promising. Thank you for posting.
How do I get hold of this article?
Time just seems to fly by! It was actually OO9 News August 2012. If you look in the letters in the next Railway Modeller there may be a smaller mention of fitting a decoder to a Kato 11-103 following on from my Dean Hill articles, failing that the edition after.
I assume Jim achieves this because Digitrax decoders are dual mode, ie they can be run on DC or DCC . A lot of decoder fitted locos have this dual mode facility but some decoders these days do not have this capability so check before you buy. Most,if not all dual mode decoders can be programmed to be DCC only and some claim this improves DCC performance. So many second-hand locos with DCC have DC disabled and will need reprogramming by a buyer wanting to use them DC. I always ensure dual mode is enabled if I sell a DCC fitted loco
Most DCC systems these days do not offer a DC option but Digitrax systems allow one DC loco to run on a DCC layout
Peter Smith
There are many confusions around DCC. My work has always been based on new chassis, such the Kato ones. Yes, the DZ125 is a dual mode decoder and out of the box you should not need to change anything.
I think mentioning DCC systems may confuse things here if you only want to work directional lights in DC.
Yes I agree Jim, just wanted to avoid possibly misleading someone once dual mode mentioned. It seems though an expensive way to get constant lighting!
Peter Smith
Being a bear of little brain, if it works then I am happy. Nobody to my knowledge has published anything in OO9 News that has worked as well for me. I also like to have the option of running on DCC if the opportunity arises.
Jim, thank you again for the feedback. I will keep a lookout for the Railway Modeller letters.
And Peter, thank you for highlighting the programming pitfalls.
There are some dots that I need to join-up on this topic, but from what I gather...
(a) A new Digitrax DZ125 decoder may be fitted (without modification) to a loco, and made to run the loco on a DC layout using a DC controller.
(b) I need to ensure 1KO resisters are fitted onto the negative pins of each LED.
Please correct me if I am wrong!
This Digitrax forum posting says that 'pulse power' controllers are NOT compatible with their decoders - something to bear in mind:
http://www.digitrax.com/tsd/KB176/analog-operation-of-digitrax-decoders/
As it happens, I have Kato chassis, waiting to be fitted to a Kerr Stuart kit sitting on my shelf - so this might be my next project :)
That looks about right.
I can confirm that fitting a DZ125Z to a Kato 11-103 is written in a letter on p1010 of the December 2014 Railway Modeller.
Good luck with your modelling.
Thank you Jim - much obliged!
Harry,
The quick answer is using a DCC decoder to control just lights from track power would like using a sledge hammer to set finish nails. If all you want to do is run low voltage lights or LED's than a resistor in line with the lamp / LED would not only be much simpler it would be much cheaper.
The whole reason for DCC is to be able to control multiple locomotives on the same track, controlling the lights and sounds are just side benefits. When using DCC there is a constant 14v AC at 5amps current in the track at all times. You control speed, direction, lights and sound at the locomotive not at the throttle.
With each DCC locomotive is assigned a separate address that it listens for and only acts when it gets a packet of information with it's address on it. On most DCC systems you can set up to 10,000 address, I personally use the locomotives number as it's address number. The advantage to DCC is that a whole layout can be wired with just TWO wires from the system to the track. What I do is run a solid core 12ga wire around the layout and then run 22ga / 24ga solid core wire feeders to the track every 6 to 8 feet.
If you have any more questions please feel free to ask them,
Andre
Portland Oregon USA
As you will have noted I broadly agree. Those most closely involved didn't want to widen the discussion
and don't want or need the main benefits of DCC. I, like you Andre, wouldn't be without them. On the other hand I don't want sound in every loco I have nor do I want to set routes or change switches with my hand set, or my cell phone!
Peter Smith
Of course I would agree as well. However, the original question related to constant light in each direction. I cannot find a method that is as small as the DZ125. At approx.
Andre, thank you for all the information regarding DCC - I will keep that posting in mind should I ever get round to adopting DCC.
Jim hit the nail on the head: achieving constant light in each direction requires several components which, when combined, are very bulky (huge, actually) when compared to a small DCC chip. (I have done this using two different methods.)
When I think of how much of my own time I devote to individual items in my modelling, the cost of a DCC chip (which might save me time and enable me to achieve something that is otherwise not possible) does not seem so exorbitant.
Food for thought, at the moment. If I do adopt this option, I will post my progress.
Thank you again for all the feedback.
If you use a DCC chip to provide lighting on a loco running under "normal" dc control, I do not think you will not get any light from the LEDs until the track voltage is (at least) greater than the Vf of the LED. DCC chips provide lighting on a DCC powered system when the loco is stationary etc., because there is always a voltage on the tracks. (As I understand it).
You are right Hugh. There needs to be a minimum voltage to switch them on but then they are constant. The problem we have is getting a constant light whilst the loco is moving and this does work using the decoder. If you want the full monty with stationary as well as moving lights then you need DCC.
On another layout I am working, in larger locos, with Express Models SureStore which gives constant light in a single direction and also stationary. However, as has already been pointed out, such boards are very large and they also maintain the light even after the loco has changed direction.
Quote from: jimowers on November 07, 2014, 14:14
I do get a constant LED light in either direction in a Chris Ward railcar using the Digitrax DZ125 decoder on DC. It also pulls away very smoothly at low speed.
I put all the instructions for installing these decoders in a OO9 News article last year.
I bought a Digitrax DZ126 and wired it up to a spare motor and a couple of LEDs on a breadboard. The motor does indeed start running after 5 volts, as per the documentation.
But the LEDs do not light up.
I asked the supplier (Douglas Stewart at Wickness Models - prompt delivery) about this and he told me that the LEDs will not work without DCC instructions.
So, Jim, I wonder if I could trouble you to tell me how you got LEDs to work?
Did you wire them up directly to the track supply? Or did you reset the decoder to allow them to work?
It will work and I have used this method several times. However, there is a trick to it. Sorry that I did not mention this before...
If you require lights on your loco then there are the three additional wires on the decoder to use.
The only problem that I found at first is that it is rather counter-intuitive in that the common wire (Blue) from the decoder here is positive rather than negative.
After you have worked this out then the rest is fairly simple
Quote from: jimowers on March 13, 2015, 14:22
It will work and I have used this method several times. However, there is a trick to it. Sorry that I did not mention this before...
If you require lights on your loco then there are the three additional wires on the decoder to use.
The only problem that I found at first is that it is rather counter-intuitive in that the common wire (Blue) from the decoder here is positive rather than negative.
After you have worked this out then the rest is fairly simple
I tried reversing the wires to the LEDs - blue for positive, and white (or yellow) for negative, but sadly the LEDs (which I checked, do function) failed to light up.
Perhaps this newer decoder model has been configured to prevent LEDs from being powered when running in analog mode.
Perhaps there is a decoder function setting that would switch them on in analog mode, but that is beyond my means - I do not have any DCC equipment with which to reset the decoder.
Heigh ho - it is back to bridge-rectifiers, resistors and LM334Zs for me.
The good news is that over the past year some tiny bridge-rectifiers have appeared that make it a lot more feasible to wire up the lights using the LM334Z method (http://www.pollensoftware.com/railroad/index.html) I have used in the past.