Train Order Signal wiring?

[peteski]

Note that, in Peteski's diagram, the physical positions of the switch controls do not correspond to the signal aspect. The switches will change the aspect, but not show it. It's not possible for the switch controls to match the aspect when one control can override the other.

That's correct. Thanks for pointing that out DKS.  It works similar to a household 3-way switch arrangement used for lights.

[Point353]

To keep it simple, I'm using @DKS latest wiring diagram (see below), the only difference being a single 3V supply that powers both the motors and the LED's.

If you're using a 3V supply to power an LED with a Vf of 3V (per peteski's prior post), then what value of resistor are you using to limit the current through the LED?

[Cajonpassfan]

Thanks guys, this is much appreciated. Yes, I have my stairwell wired the same way, per @peteski, one switch at the top, one on the bottom. That won't work here, as I do want the fascia and dispatcher switches to indicate relative orders/no orders positions.

But I think there should be a way to do what I need with a "control assignment" switch (DPDT?) probably under the fascia. Its default position would be local control, and would only be flipped to dispatch control on those days we have a formal op session. The 3V power feed would need to come off the layout side; that way only three wires ? (per direction) would need to be run into the adjacent dispatcher room. I think I know how to do this, but the signal is bi-directional, meaning there are two parallel systems, one per side. How would I wire the "control assignment" switch to control both? (I'd prefer not to have to use two switches).

As to the LED power supply, 3V is the maximum stipulated by the producer with no resistors. I believe the two back to back LED's are wired in series. Do I need to worry about burning them out with no resistors in the circuit? (At this point, I'm just using two AAA batteries to test fit the thing, eventually it will get its own 3V power supply).

Thoughts and advice welcome and appreciated.
Otto

[DKS]

Thanks guys, this is much appreciated. Yes, I have my stairwell wired the same way, per @peteski, one switch at the top, one on the bottom. That won't work here, as I do want the fascia and dispatcher switches to indicate relative orders/no orders positions.

But I think there should be a way to do what I need with a "control assignment" switch (DPDT?) probably under the fascia. Its default position would be local control, and would only be flipped to dispatch control on those days we have a formal op session. The 3V power feed would need to come off the layout side; that way only three wires ? (per direction) would need to be run into the adjacent dispatcher room. I think I know how to do this, but the signal is bi-directional, meaning there are two parallel systems, one per side. How would I wire the "control assignment" switch to control both? (I'd prefer not to have to use two switches).

As to the LED power supply, 3V is the maximum stipulated by the producer with no resistors. I believe the two back to back LED's are wired in series. Do I need to worry about burning them out with no resistors in the circuit? (At this point, I'm just using two AAA batteries to test fit the thing, eventually it will get its own 3V power supply).

Thoughts and advice welcome and appreciated.
Otto

Re: problem of switch position. Easy solution: ignore the switch position (addressing this is too complex to bother with). Just use indicator lights.

As for the LEDs, you can generally power them with most any low DC voltage; you just need to use different resistors. Also, never operate LEDs without resistors--it will burn them out.

[DKS]

Lower third is panel 1. Middle third is panel 2. Upper third is on the layout.

[Sumner]

... Do I need to worry about burning them out with no resistors in the circuit? ..

You usually want to limit the current through them to 10-20ma.  The resistors will do that and at 3 volts 300-150 ohms will work.  You'll find that resistors with even higher values will not decrease the light output all that much and the LED's are safer, probably last longer.

I have a circuit on my turntable where since I was limited in how many wires I could run to it I'm controlling two LED'S that are back to back so that with the current flowing in one direction one comes on and in the other direction the other lights. 

(NOTE the following was not worded correctly:  They are in series back to back with a wire from an Arduino to one, then to the other and then through a resistor back to the Arduino.  So far they have worked fine.)

CORRECTED:  There are two wires from the Arduino's inputs/outputs to the turntable.  At the turntable two LED's are wired to the ends of the two wires in what I have read is called 'back to back'.  They are in parallel not series as I said earlier but have their leads reversed where they connect to the two wires from the Arduino as shown next.



The sketch in the Arduino can reverse the polarity of the output on the two wires causing one or the other LED to light depending on which is positive and negative.  You could use one resistor as shown above or I've seen some schematics with the same or a different value resistor in the path to each LED.  I used two as shown below in the wires going to the junction where the LED's connect  to avoid having to try and mount them also in the turntable itself.



If you want one light to be brighter than the other (my situation) you can run two resistors in parallel with a diode in series with one of them as shown above.  The diode blocks the current in one direction on one of the two resistors resulting in more current in one direction than the other and one LED is brighter than the other.  This is shown here.....

http://1fatgmc.com/RailRoad/Turntable/page-3.html

Sumner

[DKS]

Here's a version showing the signal LED (top most LED) as part of the circuit. Again, you can use any voltage as long as the resistor is correct.

[peteski]

As to the LED power supply, 3V is the maximum stipulated by the producer with no resistors. I believe the two back to back LED's are wired in series. Do I need to worry about burning them out with no resistors in the circuit? (At this point, I'm just using two AAA batteries to test fit the thing, eventually it will get its own 3V power supply).

Thoughts and advice welcome and appreciated.
Otto

The 3V LED is a simplification (usually made by hobbyists who do not have full concept of how LEDs operate).  Also if the LEDs were wired in series, they would require higher voltage (double of what each LED requires).  If they were wired back to back then they would  not light up at all (at least that is how I understand "back to back").  The 3V rating  for white LEDs is a "typical forward voltage rating", not an absolute value.  Typical white LED will likely start to glow around 2.5V and some higher current LEDs can have 3.5V or more across them while they operate at their rated current. 

I posted a fairly extensive write-up on powering the LEDs in the first reply to your initial post.  Actually most of the first page of this thread is dedicated to the subject.  But if you don't feel like re-reading it (or it is too technical), then just install a 1000 ohm (1k ohm) resistor in series with the LEDs in the signal.  I'm talking about the LEDs on the signal mast (not the indicator LEDs in the fascia).  Then connect a 9V battery to light up the LEDs and measure the voltage across the leads going up to the mast.  We are doing this to figure out whether the 2 LEDs up there are connected in parallel or in series.  If the voltage reads less than 3V then the LEDs are in parallel.  If the voltage is greater than 3V then they are in series.  We can then figure out what resistor to replace the 1K resistor with to give you the desired brightness at the voltage you will be using to power the.  If the LEDs are in series then 3V will not make them light up.

Sorry for the lengthy instructions, but I just cringe when I see poor LEDs possibly being abused.    I see frequent LED abuse in our hobbies. People do not understand how LEDs work, and the misinformation spreads like wildfire.  No LED should ever be connected directly to a source of voltage (power supply) unless it is a constant-current (not a constant-voltage) supply.  Constant-current supplies are the type of power supplies dedicated to power LEDs, while constant-voltage supplies are the ones hobbyists use to run model trains and related accessories.

When using constant-voltage supplies, LED should never be connected without a series current-limiting resistor.  Yes, there are lots of examples of white LEDs being connected directly (no resistor) to a small button-type 3V batteries.  Like a CR2032. That is ok, because that type a battery can't supply a lot of current due to its high internal resistance. Think of it as the resistor being built into the battery.  But if you power your LED with a 3V wall-wart which is capable of supplying 50mA or more, then the LED will need a dedicated series-connected resistor.

[DKS]

As to the LED power supply, 3V is the maximum stipulated by the producer with no resistors. I believe the two back to back LED's are wired in series. Do I need to worry about burning them out with no resistors in the circuit? (At this point, I'm just using two AAA batteries to test fit the thing, eventually it will get its own 3V power supply).

Thoughts and advice welcome and appreciated.
Otto

With all due respect to Dirk, there should always be a resistor in the supply circuit for LEDs. Furthermore, the supply voltage need not be limited to 3 VDC; you can safely use a 12 VDC source, as an example, with the proper resistor. Also, there is no need for a dedicated power supply for the LEDs.

Peteski has covered all of this in great detail; I'm merely summarizing.

[Point353]

I posted a fairly extensive write-up on powering the LEDs in the first reply to your initial post.

Sorry for the lengthy instructions, but I just cringe when I see poor LEDs possibly being abused.    I see frequent LED abuse in our hobbies. People do not understand how LEDs work, and the misinformation spreads like wildfire. 

Wouldn't the equation you posted in reply #1 lead someone (who doesn't know any better) to calculate/conclude that zero is the correct value of series resistor for an LED with a Vf of 3V when operated on a 3V power supply?

[peteski]

Wouldn't the equation you posted in reply #1 lead someone (who doesn't know any better) to calculate/conclude that zero is the correct value of series resistor for an LED with a Vf of 3V when operated on a 3V power supply?

I guess it would.  But then if the LED's Vf (for its operating current) was exactly 3V then the equation would be correct and the circuit would work correctly.

I get your point though - I modified #1 post to reflect what you stated.

[Sumner]

..........If they were wired back to back then they would  not light up at all (at least that is how I understand "back to back")....

Yes you are correct and I went back and corrected my earlier post above as it was misleading and inaccurate as posted.  I found the term 'back to back' used in a couple different places such as here...

http://www.trainelectronics.com/artcles/ditch_lights/index.htm

As you mentioned it isn't probably the best term to use.  I wired two of the turntable lights in this manner some months ago and obviously had forgotten how exactly I'd done it.  I should have gone back and refreshed my memory before posting above.  I think I have that post straightened out some now but I'm open to comments on it. 

Sumner

[Cajonpassfan]

For what it's worth, when I used the term back to back, I was referring to the physical arrangement of the LED's atop the TO signal, with the lights, lenses and blades facing in opposite directions, east and west.

But, it turns out there is only one LED there, so all that is moot.
Sorry if this caused some confusion.

I'm still studying the latest diagrams @DKS had kindly provided; thank your David.
Otto

[peteski]

Yes you are correct and I went back and corrected my earlier post above as it was misleading and inaccurate as posted.  I found the term 'back to back' used in a couple different places such as here...

http://www.trainelectronics.com/artcles/ditch_lights/index.htm

As you mentioned it isn't probably the best term to use.  I wired two of the turntable lights in this manner some months ago and obviously had forgotten how exactly I'd done it.  I should have gone back and refreshed my memory before posting above.  I think I have that post straightened out some now but I'm open to comments on it. 

Sumner

Actually Sumner, in the example you cited,  the LEDs *ARE* connected back-to-back. That is a correct terminology for that arrangement.  Well, each leg of the circuit also has a series resistor.  To be accurate, that circuit depicts 2 series connected resistors/LEDs, connected in parallel.  A true back-to-back LED connection would not have the resistors with each LED.

Speaking of that, the person who designed this circuit is likely not very familiar with electronics.  2 resistors are not needed., They could be replaced with a singe resistor on one of the wires feeding the back-to-back LEDs.

[Cajonpassfan]

Re: problem of switch position. Easy solution: ignore the switch position (addressing this is too complex to bother with). Just use indicator lights.
...

Well, call me old fashioned, or weird, but I really like the simplicity of a physical, tactile interface a nice DT switch provides to simulate operation of a manual train order signal. Orders UP, No Orders, DOWN, simple, end of story.

Sooo, I'm not too keen on the "easy solution" of ignoring the position and relying on lights. As I noted earlier, I thought a simple "control assignment" switch could solve my problem as it would only be used rarely.

I sketched out the diagram below to outline what I'm thinking. I got rid of the LED's (other than the ONE atop the signal which is always on) and added the load resistor (thank your guys, good advice). The "control assignment" local/dispatcher switch is somewhere below or even hidden behind the fascia, default set for Local control, and only gets flipped before an op session involving a dispatcher.

Given my rudimentary knowledge of all things electrical, I may be missing something. Is there anything in the diagram that that doesn't work?
As always, advice and comments are truly appreciated. Even at times I don't follow the advice exactly, I learn.
Otto