I am builidng a DC system and looking for ideas for a simple way to indicate the direction setting of each block, by using two different colored lights. I have considered two different ways to do this.
1. By using incandescent bulbs with diodes - a diode in series with a bulb with the direction of flow from N to S, and one diode/bulb with flow from S to N. Does this make sense? If so, can someone give me some guidance on how to select the diode?
2. Use LEDs, which I understand are current directional. Does this make sense? If so, can someone give me an idea of the range of voltage over which the LED will still light? I am thinking that LEDs may not operate (emit light) over the same range as incandescent bulbs, in which case, option 1, above, may be the better choice. Also, if this is a good approach, can someone give me an idea of how to select the LEDs.
Thanks, in advance, for everyone's response.
The easiest solution would be to use bi-color LEDs. They basically combine a red and a green LED in one package, oriented to opposite polarity. That means, when you apply current in one direction, it lights red, and in the other direction, it lights green. Wire it in parallel to your block (with a resistor to protect it from high voltage) and it will indicate what direction the current is flowing.
--Steven Otte, Model Railroader senior associate editorsotte@kalmbach.com
Thanks, Steve. this does seem like the easiest solution and I appreciate the idea. Can you give me an idea of the voltage range over which LEDs will light? For instance, assume that I am using a 5mm LED with a votage (FV?) of 1.8V. Will it still light when the voltage is only 1.5V, 1.0V, etc.?
Where are you mounting this indicator? On the Layout or on the control panel?
On the Layout Id mount a pair of signals, green facing one way , red facing the other. Power them from the tracks, I think not, I would power them from a separate power source and tie it in to the same switch that controls the direction switch.
Of course, it is easy to see how the power is set by which way the train is moving.
Layout of LION is a SUBWAY layout, trains can ONLY move in the correct direction. There is no option for moving equipment in reverse. Left rail is GROUND; Right rail is THIRD RAIL (+8-12v dc).
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Thanks for your response. I am mounting the indicators on the control panel. I thought about the idea of powering them separately, rather than from the track power circuit, since that way they will always be on full brightness, regardless of the voltage to the rails. The question is, how to I tie the indicator circuit into the the direction control circuit, for which I intend to use DPDT (center off) switches. Any ideas on that?
Thanks
With an approriate size resistor, an LED can operate over a fairly wide range of voltage without problem. For example, a 560 ohm resistor will allow the LED to light up from under 4 volts to the rails up to a full throttle voltage that might go as high as 13 volts.
One way you can implement this as a simple signal system would be at the gaps between each block, wire a green LED diagonally across the gap - left rail on one side of the gap to right rail on the other side of the gap, and a red LED across either of the gaps - right rail on one side to right rail on the other. Now, oif the two blocks are set for the same polarity, the green LED will light, and of they are set opposite, the red LED will light. You need two sets of red and green LEDs, each wired the opposite way, the only downside is that if you are looking at a signal and the blocks are both set so that a train is coming at you, not from behind you, neither LED will light - but the one wired the opposite way around, facing the other direction, will be lit.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thanks, again, for all of your input to my earlier questions regarding polarity circuits. I have two follow-on questions regarding LEDs. First, I suspect that there is a lot of diference in the quality of LEDs depending upon the manucturer. Is there any way to get an idea of the quality of the ones that I buy? Perhaps by some standard that may be referenced or perhaps by the reputation of the supplier or of the manufacturer.
Second, up to now, I have purchased 10mm LEDs because I want to be sure that they are clearly visible for whoever may be operating - short and tall folks and figured that the larger the LED the more visible it will be. I have now designed a circuit for checking polariy in a cross-over (change of direction) circut that I can build with either (2) red and (2) green LEDs or (2) two-color (red-green) LEDs. However, the supplier that I have used doesn't have 10mm two-color LEDs. Does anyone have a suggestion as to where i might find them. It is not a big deal, of course, I can always use the (4) LED design.
I've never had a problem with LEDs that I've bought. Simply for convenience, I get most of them from my (now gone) LHS from Miniatronics. I've also gotten them online.
My only question with doing this in DC is that they will not light when the trains are stopped, because the DC voltage will be zero.
It takes an iron man to play with a toy iron horse.
I did this many years ago with two lead red/green 20 ma LED's with TTL circuits for controlling the LED's. Used 74LS240 drivers which use 5 V DC. Probably more than you want to do.
Club had fourteen blocks with sidings and all single or double target poles.
Since many use 12 vdc for accessories, A 1k, 1/4 watt resistor with work.That allows about 9 ma for a 20ma LED.
LED resistor calculators are all over the Internet.
Edit.
I just remebered we had a DC system and a dispatcher at the control panel. An operator had to request a block.
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.
MisterBeasley I've never had a problem with LEDs that I've bought. Simply for convenience, I get most of them from my (now gone) LHS from Miniatronics. I've also gotten them online. My only question with doing this in DC is that they will not light when the trains are stopped, because the DC voltage will be zero.
Continued thanks for the replies to my latest post regarding LEDs. All things considered I have decided to use the (2) red and (2) greed LED approach I am aware of the problem with LEDs not lighting if the train is stopped. However, my plan is to have a very simple operation I will either stop the train in a block before the crossover and then make the swithch, or else operate the train at the slowest speed that will allow the LEDs to show and then switch on-the-fly. It was good the hear that LEDs quality hasn't been a problem.
I appreciate the responses regarding circuits and devices to keeps the LEDs lit - including the mention of the relay. However, since I am trying to keep the electronics simple I will probably not take that route.
Cheers,