Nice!  Thanks for sharing!

Nice!  Thanks for sharing!

This was one of my next projects!l

Thanks for the research!

Thanks

It seemed fairly easy to do from what I saw in the diagram plus I already had the items needed, so I did it and it worked.  Thank you for watching....John

Future Projects

Glad to have helped. Thanks for watching...John

LEDs. And Diodes

Since the LED is a diode, I don't believe you need the diode, just the LED and resistors and it should work fine.

I'll try that

I followed the diagram that I found but I will try this method too to see if it works.  Thanks.

Turnout position indicator

Thanks for sharing. I am going to head out and wire a couple of turnouts as soon as I finish breakfast.

Jim 

Or a dwarf signal as a switch position indicator

Might take another look at using this to light a BLMA US&S dwarf searchlight signal for a distant turnout switch indicator.

With DCC you really need diodes

If you are running with DC then the circuit as shown is fine.

However, with DCC the voltage is alternating positive and negative across the rails, so that the LEDs are reverse connected for half the time - and most LEDs are only rated for a few volts in reverse - and not for the full DCC voltage - and this is likely to shorten their life (if not cause immediate failure.

You should connect a diode in parallel with each LED - not in series as shown in the original published circuit. This means connecting the anode of the diode to the cathode of the LED and vice versa - as per the connections shown in the picture below -

DCC Electrical Fun - Clarification

Commentor jterryc said with DCC you really need diodes.  Have you tried this with trains running, and DCC power supply on?  There seems to be a difference of opinion on this.  Commentor Brentglen say you don't need diodes because the LED is a diode.  Can we clarify this for sure?

Phil in Ohio

DCC Electrical Fun - Clarification

You really should install the diodes to protect the LEDs from failure due to reverse over-voltage.  As explained in another post, LEDs have a very low reverse voltage capability and without the protection diode you will at least experience a shorter life and possibly complete failure.

Dale Gloer

Clarification - Diodes

Yes, the LED is a diode, but with a low reverse voltage rating - with the diode connected across the LED (in reverse, as described) the diode conducts when the DCC voltage reverses and clamps the reverse voltage across the LED to the forward voltage of the diode - less than 1 volt. This protects the LED and ensures it does not fail prematurely.

This is just good electrical practice (I am a retired professional engineer - electronics and computer systems).

LED signal indications for finger-throw switches

Given Mssrs. Metzel and Chamberlain's comments above...could this or similar circuitry be used for single bi-color (red/green) LED pot or dwarf signal for a yard switch?  Could a single resistor and diode be used in parallel with the frog side of the circuit with DCC?  I used to use a diode circuit for constant lighting boards using DC, where the change of DC polarity through two diodes aligned in opposite directions would result in forward or reverse headlight selection.  If so, a circuit diagram for that arrangement would make yard track signaling very do-able.

Full disclosure, I too can follow most circuit diagrams, but am not particularly electronically astute.

LED Turnout indicators

We do a similar circuit for our reverse track sections on the wye on our layout. We place the LED's at the entrance and exit of the reverse section of track on our wye so our operators know if it is clear for entering. When the LED is lit, then the polareity is OK and your loco can enter the reversing section of the wye. While the loco is in the reverse section you can then throw the reverse toggle and finish turning your loco. The operators love it as it gives them an added operation for turning their locos. Yes, we could have used an auto reverser, but this is more fun!

Make Murphy Work Harder

I can see from the diagram that when one LED is ON, the other isn't because both feeds to it are the same polarity. Works for either position of the points. When the points aren't touching either stock rail the LEDs are both off, because there's no feed from the frog. This is fine, except that the rails, and the trains, and dropped tools, and whatever else don't read the diagram. Who can predict what, e.g., a derailment might do? Seems like the suggestion of Terry, P.E., is a very inexpensive way to help guard against unforeseen mishaps.

For reliability I would watch the contacts between points and stock rails. Our club has PECO turnouts, and we have found that an occasional swipe with a graphite pencil inside the contact areas helps maintain continuity.

DrJolS 

LEDs and DCC

It is correct that the LEDs may breakdown in a DCC application, because most LEDs are rated at 5V reverse voltage. The current limit provided by the resistor would keep the LED from catastrophic failure, but would probably reduce life. However, the 5V reverse voltage spec is an extremely conservative spec used by the manufacturer so they do not need to measure the parts. In fact, many LEDS do not reverse breakdown at 20V, and a given part number will be fairly consistent from part to part. It would be simple to measure the reverse breakdown on the LEDs used, by just placing the diode-resistor combination across a power supply in reverse voltage, and slowly turning up the voltage and measuring the current. Breakdown occurs as soon as the current reaches maybe 10 ua. If they do not break down at 20V then you do not need an extra diode.

LEDs on track ties

A couple years ago I faced the same situation (which track). I came of with a similar circuit but used 0603 SMD green LEDs buried between the outside ties. Eliminated the need to run wires all the way to the fascia.

Bob

Reverse Current?

In the original circuit with the diodes in series, wouldn't the diode block the reverse current completely so it would not be a problem?  Isn't  this better than the diode connected in across the LED in the reverse direction?   What don't I understand?

Bill

Back biased LEDs

When I did my building simple circuits writeup, I used this problem for the example. During testing, I discovered that the reverse phase of the DCC signal would make some LEDs glow a bit. An extended web search failed to find any examples of LEDs failing under these conditions, but the idea of including a series diode for protection was widely recommended. I added 1n415s and the glow went away.

Many LED tech sheets quote a reverse voltage of 5v, and show a zener diode included to protect the LED from damage.

Incidentally, a bi-color LED should work fine. Either common anode or common cathode will do, because the direction of the LEDs is immaterial, as long as everything points the same way.

pqe

Amazing! This method work so well

Thank you for posting this for all of us to use. It is so easy to do and works very well. I have always wanted to do something like this because I did not want to buy tortoise switches since I like using manual throws. Once I found this video and tried it I was instantly excited and happy with the results. I now wire all my switches to be able to accept dwarf lights even if Im not going to use them right away. Thanks for the video and forum post and keep up the good work!!

Joe G

-Arizona-

What about the power draw?

I had thought about doing just this on all my Peco turnouts a few years ago but stopped short because I couldn't figure out if my power supply would handle 50+ LEDs sucking power from the track while up to 5 locomotives were running at the same time.  So maybe someone could answer this question:  How much power (amps) does a small(ish) LED as shown in this example draw?  Could one over tax a power supply using this technique with around 50 trunouts? 

Yes, you do need reverse bias protection diodes!!!

I am an electrical engineer. Terry's comment is correct - when the polarity is reversed, no appreciable current flows, so the resistor doesn't drop any voltage (a common spec is 10ua max, so typically it will be much less). The full DCC voltage appears across the diode. And, as Terry stated, most LEDs will not take 12v or 14v reverse bias for long. If you don't want to buy signal diodes (although they are very cheap - 100 for a couple dollars on EBay), you can always put another LED in parallel but with the opposite polarity directly across the indicator LED. I have seen this mistake many times. Eventually, the LED will give up. I just surveyed a half-dozen LED data sheets, various colors and sizes, and they all specified a 5v maximum reverse voltage. This is especially important if you are wiring signal heads where a bad LED will be difficult to replace.

Here is a simple circuit I use to drive dwarf signals directly from my Tortoise supply. Most signals have a common anode. The two additional signal diodes allow the Tortoise polarity to light both LEDs and protects them from reverse over-voltage. 

For a panel indicator, just wire the two LEDs back-to-back (parallel) with the limiting resistor in series, then wire right across the Tortoise. Easy.

Hope this helps.

Jeff

P.S. Here is a link to an EBay auction. These are 300mA signal diodes (Your LED should be limited to 20mA, I use 10mA). They are 100 for $3.49 with free shipping. Don't know the seller, this is just to give you the idea.

http://www.ebay.com/p/1n4148-diodes-100-pcs-philips-with-us-seller/1400257279?_trksid=p2047675.l2644 

Diodes

Diodes are cheap, so it doesn't hurt to put them in. However, I installed LED indicators like this about 5 years ago, without diodes, and they are still working fine. I may have used a higher voltage rated LED. Like 12 volt rated, but I don't remember, it was 5 years ago and I have trouble remembering what I had for breakfast let alone something from 5 years ago.

Built in these

LED's  are a full wave bridge rectifier, a filtering capacitor and a resistor. Just hook the wires up, no cathode,  or anode orientation to worry about........my kind of wiring.....

I have an HO layout using Shinohara insulated frog turnouts, and FastTracks switch machines. More sophisticated wiring of the switches & layout is further down the road, but for now I wanted an easy way to see the position of the mainline turnouts at a glance. Ironic this post showed up when it did, I just finished the wiring of the LED's a week or so ago.                                                                                                                            So, I have green, lined for the mainline side, yellow, lined for the turnout side...........

Iv'e been running a train since completion of the indicators and have had no problem. Lights are steady with engines in a forward or reverse mode. These are the 3 mm bulbs, drawing 20 milliamps each.......