Train Order Signal wiring?

[Cajonpassfan]

I’m pondering how to power and wire the exquisite new Train Order Signal from ATSF N Scale. It’s bi-directional, essentially two semaphore blades back to back, with two identical but independent mechanisms driving them. Each also has a tiny white LED with color changes from green to red accomplished by colorized lenses in the blades, like the prototype. A 6V DC geared motor drives each blade via a rocker arm and the LED’s are rated at “flat 3V max.” whatever flat means...

On my layout, these signals need to be operated manually from a remote location. I’m thinking each signal is controlled by a DPST switch to reverse polarity for the motor (but not the LED), with some kind of an on/off switch actuated by the rocker arm to cut off power to the motor (but not the LED) when the blade reaches its desired positions (horizontal/red or diagonal/green).

Here’s the challenge. Ideally, I’d like to use one power supply, around 5V to drive the motors, with resistors to drop the voltage to the LED’s to around 2.5 V to be on the safe side. (Burning it out is not an option, it can’t be replaced without major damage). Also, when the DPST is reversed, the cut-off switch needs to be bypassed, presumably using diodes? That’s where my rudimentary knowledge of electricity gets fuzzy, and I’m concerned about power spikes possibly impacting the LED voltage when the motor is in use? Do I need two separate power supplies to be safe?

Pics below. Thoughts, suggestions and ideas on how to wire these things will be appreciated.
Thanks, Otto

[peteski]

Otto,
You ideas about how to power the motors are spot on. DKS uses this type of circuit in his animated models, but his write-ups in the animation section do not provide those kinds of details.  Hopefully he will chime in to give you more details.

I'm chiming in to comment on how to power LEDs (in general).  As you know, best and safest way to power LEDs is to use a series-connected resistor with the LED.  But that resistor *IS NOT* to reduce voltage - it is to limit the current passing through the circuit (and through the LED).  LEDs are devices that operate on current (while developing certain known voltage across them while they are operating).  While the voltage and current values are related, one should really think about the current that will pass through the LED (and the voltage will take care of itself).

For calculating resistor values, white, blue, and true-green LEDs have about 3V across them.  Other color LEDs like red, yellow, amber, orange, and standard green have about 2V across them when operating.  That voltage is usually called Vf (or Forward Voltage in  the LED specs). While there are some variations depending on the brand of the LED, those voltages values are good to use in most cases without looking up any technical specs. The Vf is the basic value needed for calculating the LED's current-limiting (not voltage dropping) resistor.

The other value is the Power source's voltage. I'll call it Vss.  For practical purposes the Vss should be higher than the LED's Vf by at least 1V.
The LED current will be If, and the resistor value will be R.

The maximum safe current the LED can pass (and which will produce maximum brightness) is also specified in the technical specs.  Very small LEDs (SMD 0201, 0402, and some 0603) have If of 5mA, larger ones (0603, 0805, 1206 and larger) can have If of 10mA, 20mA or larger). But for out purposes, we seldom power them using the maximum current (they would be too bright for our applications).  How much current do we want?  That is something that is up the the individual taste.  So, some experimentation is needed to determine what will look good.

The calculation is simple.  R= (Vss-Vf)/If
If you have a single white LED, the supply voltage is 5V and you think that 2mA (or 0.002A) would produce the desired brightness, then the resistor value will be:
(5 - 3) / 0.002 = 1000 ohms (or 1k ohm).  This resistor will assure that a safe current will pass through the LED.

I hope this explanation is helpful to you making sure your LEDs do not release the magic smoke.

[carlso]

Nice write up peteski!

Carl

[Cajonpassfan]

Thank you for the nice response, Peteski, much appreciated! It’s good to have the concept validated.
So tonight I dug up a couple of old wallwarts, 5V and 6V output supposedly and decided to check the output voltage before testing the motors and LED’s. I’m getting 13V and 20V output readings respectively! Wth? Excuse my ignorance, but is this because there’s no load, or has my multimeter gone bad?  I’m a bit reluctant to use them, for obvious reasons...
Otto K.l

[MK]

It's because they have no load.

[Cajonpassfan]

Okay, that’s what I thought. But if I’m going to test the LED’s with a 1K Ohm resistor as noted above, will the LED’s be safe?
Thanks for your feedback...
Otto

[Point353]

Okay, that’s what I thought. But if I’m going to test the LED’s with a 1K Ohm resistor as noted above, will the LED’s be safe?
Thanks for your feedback...
Otto

Measure the output voltage of the wallwarts with just a 1K ohm resistor as a load, before you connect the LEDs.

[DKS]

Otto, I'm seeing a whole bunch of wires coming from the unit. It's difficult to tell from the photos, but it appears some rudimentary indexing is already provided. Can you post the documentation that came with the unit, and/or post a close-up photo of the underside of the unit so I can see what's going on with those wires?

[DKS]

Thank you for the nice response, Peteski, much appreciated! It’s good to have the concept validated.
So tonight I dug up a couple of old wallwarts, 5V and 6V output supposedly and decided to check the output voltage before testing the motors and LED’s. I’m getting 13V and 20V output readings respectively! Wth? Excuse my ignorance, but is this because there’s no load, or has my multimeter gone bad?  I’m a bit reluctant to use them, for obvious reasons...
Otto K.l

Wall warts are usually unfiltered DC, which is why the voltage readings are so wacky. While you can power LEDs with them, it's much better to use at least a filtered and preferably regulated DC source. I would invest in a filtered/regulated power supply for your signal system; they aren't costly.

Example:

https://www.ebay.com/itm/DVE-Power-Supply-Model-DV-51AAT-Input-120VAC-Output-5VDC-1A-Regulated-5-Pin/164376343610

Here's one that delivers 5VDC and 12VDC, which could be quite useful.

https://www.ebay.com/itm/5VDC-12VDC-Regulated-Table-Top-Power-Supply/223707146567

[Cajonpassfan]

Thanks guys, appreciated!
David, the wiring is quite simple: six wires in, a pair to each motor, a pair to the LEDs. see pic below. Sorry about the photo quality.
As to specs, there aren’t any other than a cautionary note to never exceed “flat” 3V DC, and there’s definitely no indexing. Dirk’s is a small operation and to keep the cost reasonable, he’s choosing to provide just the basic mechanism for the buyer to finish. More at atsfnscalemodels.com

Thanks also for the power supply advice and link, I may yet go that route. How does one tell whether a supply is filtered? I have a box full of them and planned to use the one below from my old BlackBerry...remember those? It does have an impressive array of logos and certs on it

Otto

[peteski]

Most generic USB chargers use switchiing-type power supplies (that produces filtered and regulated 5V DC) and they just cost few dollars each.  Most cell phones/smart phones from the last couple decades use those, so you might have one from an old phone lying around.  They usually supply 1A of current, which shoudl be more than you need.

Here is a 5V 2A one for $4 (plus shipping of course).  https://www.goldmine-elec-products.com/prodinfo.asp?number=G19740  Just cut the plug off, and hardwire it.

[DKS]

David, the wiring is quite simple: six wires in, a pair to each motor, a pair to the LEDs. see pic below. Sorry about the photo quality.
As to specs, there aren’t any other than a cautionary note to never exceed “flat” 3V DC, and there’s definitely no indexing. Dirk’s is a small operation and to keep the cost reasonable, he’s choosing to provide just the basic mechanism for the buyer to finish. More at atsfnscalemodels.com

OK, now I see what's going on. As long as you're not adverse to attaching a couple of brackets with a few micro-switches on them, then I can come up with a plan for you.

One quick question: do the mechanisms allow the motors to turn a full 360 degrees in one direction? It looks like it, but I can't be certain. That would greatly simplify wiring.

[DKS]

So here is the absolute simplest way you can make the signals operate.

Assumption 1: the drive motors can run 360 degrees in one direction, without the need to reverse.

Assumption 2: you have no problem attaching a bracket with three microswitches to the signal assembly.

Assumption 3: you have no problem using a rotary switch to control the signal aspect.

Mechanical requirements: attaching a bracket for each signal to mount three lever-type SPDT microswitches. One microswitch (green) is mounted so that it is thrown when the actuating lever is in one extreme position; another (also green) is mounted so that it is thrown when the actuating lever is in the other extreme position; and the third (blue) has had its lever modified such that a piece of styrene tubing (red dot) mounted to the signal's actuating arm can slide past the microswitch and throw it when the mechanism is in the middle position.



Wiring diagram:



Note 1: polarity makes no difference in this scheme. It will function properly regardless of polarity.

Note 2: 3 VDC will work instead of 5 VDC.

[DKS]

Microswtiches:

https://www.ebay.com/itm/10PCS-V-153-1C25-Limit-Switch-Long-Straight-Hinge-Lever-TypeSPDT-Micro-Switch-SE/303677912298

https://www.ebay.com/itm/Gikfun-Micro-Switch-Long-Hinge-Lever-Pack-of-20pcs-for-Arduino-EK1713/254429791149

https://www.ebay.com/itm/10x-Limit-Switch-Long-Straight-Hinge-Lever-Type-SPDT-Micro-Switch-TOP-V-153-1C25/293576063210

Rotary switches:

https://www.ebay.com/itm/Rotary-Switch-4-Pole-3-Position-Break-Before-Make-With-Set-Screw-Pointer-Knob/193241773298

https://www.ebay.com/itm/Philmore-30-15203-2-Pole-3-Position-Non-Shorting-Rotary-Switch-0-3A-125V-AC/264526499290

[Cajonpassfan]

Thank you, David, for taking the time. Wow, nice graphics and an interesting  approach. So the motor goes around in one direction only, at the cost of three micro switches and a three position rotary switch. Thanks for the links, too.
It’s certainly electrically simple, but the three position rotary switch turns me off, no pun. I’d really like the signal switch activated by the operator who is in another room to have just two positions: orders or no orders, blades up up or down. Center off would be okay, just to turn the power off when desired. That probably means the motor needs to reverse direction, and just two “end of run” micro switches?  Can the motor polarity be driven by diodes, ie the motor power is turned off by the micro switch, until reversed? I have a vague notion that might work...?
About your Note 2: 3V works, but the blades move really slow...that maybe okay...
Thanks again, Otto