# Need help adding additional pair of LEDs to flasher circuit



## Never Get Old (Apr 16, 2016)

Hi All,

Rob Paisley published this ingenious circuit to flash 2 pairs of LEDs for a bi-directional flashing crossbuck using only two wires, which in N scale is very nice. However, I want to flash three pairs of LEDs for an over-the-road cantilver grade crossing signal instead of just the 2 pairs he showed for a crossbuck. Diagram 1 is his original circuit.

Have I added the additional LED pair in the proper configuration in my second diagram?

The next part of the question will be how to add an additional three pairs of LEDs for the cantilever that faces the opposite direction. Have I added them in the proper configuration in my third diagram, and will the 555 ICs be able to drive the six LEDs that are on at any given time?

All are identical red LEDs since it's for a grade crossing.

Thanks.

-Never Get Old-




*Here is Rob Paisley's original circuit with just 2 pairs of LEDs. The left 555 portion of the circuit has been extracted from his old 2004 flasher circuit board, which I had to retrieve from the Archive.org Wayback Machine capture of his old site. The LEDs are all identical and all are red since it's for a grade crossing.*
























*If I want to add a third pair of LEDs to his circuit, it seems like this would be the way to do it.*














*What I actually need is to flash 6 pairs of identical red LEDs for two N scale over-the-road cantilever grade crossing signals, and I am wondering if this would be the correct way to add the extra LEDs that I need, and if the two 555 ICs are capable of driving the 6 LEDs that will be on at any given time. His circuit below remains unchanged except the number of LEDs. The LEDs are all identical and all are red since it's for a grade crossing.*


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## T-Man (May 16, 2008)

That is what a bread board is for. To connect a circuit up without solder and see how it works.

WHen you look at the pairs up and down you only need one wire left to right between the pairs.

I am not sure about the two 555's. You should start on what is the original circuit.


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## Never Get Old (Apr 16, 2016)

Diagram and concept before breadboard test.

I have updated the original post to clarify my question.

-Never Get Old-


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## T-Man (May 16, 2008)

Are the LEDs all the same color? If not they will have a different brightness.
The LM 339 is obsolete. Remember only half of the LEDs are lighted at the same time.
I use the back to back wiring of the LEDs for AC operation.
The two LEDs and the resistor is basically my track tester for polarity in DC.
In house lighting I have used four pairs with one resistor. Maybe 8 it has been a while.


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## Never Get Old (Apr 16, 2016)

I have updated the original post to clarify my question.

-Never Get Old-


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## T-Man (May 16, 2008)

For the next three pairs I would wire them in parallel between the number three and use a second 1k resistor.
TO do this disconnect the wire from the top pairs to the low pairs under the resistor, and run a 1k resistor from the bottom pairs to the 10k and next to the other 1k.
That will enable easier troubleshooting. 
You still show double wires between pairs you need only one which was shown in the Bob Paisley diagram.


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## Never Get Old (Apr 16, 2016)

Thanks. I had a feeling that I needed that second 1k resistor when adding the second set of three pairs for second signal.

I'm concerned about the ability of the 555's to drive the 6 LEDs that will be on at any given time. 

If this works, I will then convert the circuit to a single 556 IC instead of using dual 555s. One step at a time.

As for the extra connections from LED to LED on my diagram, I was trying to figure how the leads from the LEDs physically might be soldered together. From an electrical standpoint, yes, only one connection as Rob showed.

-Never Get Old-


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## T-Man (May 16, 2008)

I read the notes on the Paisley page and 200 milliamps was mentioned. You are only drawing 20. That is why the breadboard is important to see how the lights work. That information would be in the 555 datasheet. You are only powering 6 at a time not 12. I am not sure why a 556 needs to be used?? I bought my 555's in a pack of 50. No big deal to use two. 
Ebay has all these under 5 buck solutions. I was expecting one any minute in this post. Be certain there is is more than one way to flash.

You never mentioned the light itself. I am guessing you want three LEDs to alternate flash from center to both ends. That is a cool way to do it.


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## T-Man (May 16, 2008)

When Radio Shack was around I used their 1/2 watt resistors. Now I use 1/4 watt. There is a way to calculate a safe load for resistors but I just go with practical use.
Keep in mind if you split your pairs it will take six wires.
Of course this has to work with track detection something I have not started in HO.


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## T-Man (May 16, 2008)

Do have values for the flash frequency? The cap, R 14 and R16 control that.


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## Never Get Old (Apr 16, 2016)

1) I want this circuit because it's a 2-wire solution. Running multiple wires inside 1/16" tubing isn't easy. If the circuit is correct, I will post a diagram of how the signals will be wired internally. Off-the-shelf solutions are not 2-wire.

2) I do not need train detection as I have a small, double oval, continuously running display layout where each signal would be on 99% of the time due to one train or the other.

3) Yes, I have the flash frequency values. I used an online calculator for that instead of a variable resistor as I don't care to vary the frequency. I'll publish those as I continue to work on my drawings.

4) I probably will use a single 556 IC for simplicity on a tiny circuit board.

5) I miss being able to go down the street to Radio Shack to pick up something and not have to wait for days for a shipment in the mail, and pay shipping costs.


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## T-Man (May 16, 2008)

For small tubes I used enameled wire. Thinner than insulated wire. That is a small tube. Good Luck!


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## Never Get Old (Apr 16, 2016)

Yes, I bought the enameled wire in red and green. It's so fine (30 AWG) that it's not easy to work with. Neither are surface mount LEDs. Welcome to N scale. I have 3D printed signal targets that fit onto 1/16" K&S tubing for flashing crossbucks and they also fit 3/32" K&S tubing for the larger over-the-road cantilever signals.

-Never Get Old-


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## Never Get Old (Apr 16, 2016)

Values for the capacitor and resistors.










-Never Get Old-


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## Never Get Old (Apr 16, 2016)

Ah hah! Thanks to Rob Paisley. I emailed him, and he replied with a few suggestions. First, be sure to use the second resistor for the second set of three pairs, which we had thought was needed. Second, he suggested 330 - 470 Ohms for those resistors instead of 1 kOhm. I don't want these LEDs to be glaringly bright, so I'll try an assortment of different resistors. They are cheap enough to order various values.

His answer to the updated diagram below was,

*Should work OK.*

*Rob.*

So, now we go to the next step, figuring out how to orient the LEDs on the masts and run the wires inside, which I will go draw now that the circuit is ready.


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## Never Get Old (Apr 16, 2016)

So, if I have everything oriented and connected correctly, I end up with this easy-to-wire configuration. I say "easy" because notice that there are only 2 wires inside the mast at any point, and in N scale that's a huge benefit. Also, if I use LEDs with leads instead of SMD LEDs, I can simply solder the leads together in a number of locations, which makes things fairly easy. I have samples of LEDs with leads and without leads, and although the ones with leads are much more expensive, they sure are easier to handle because they are only 1.6 millimeters. I thought about putting 8 LEDs over the road instead of 4, but it's a compromise I am making for ease of construction.

If someone here has a keen eye for wiring, see if I have translated the circuit above correctly to the connections shown below. Flashing should be all 6 left LEDs then all 6 right LEDs.


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## T-Man (May 16, 2008)

I think that is great that you got a reply. 
About the wire being fine, I used an Xacto blade on the wire to strip it. The wire would be on a flat bar and I would twist the wire to strip it all around.


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## Never Get Old (Apr 16, 2016)

If I have all of this correct, the circuit and wiring are wonderfully simple for this relatively complex N scale task. 

I think I have translated the two 555 ICs to a single 556 IC and the whole thing will easily fit on a tiny perf board, which I have. I have 30 AWG magnet wire in red and green to run inside the masts. I have the 3D printed targets and brackets to hold the 1.6 mm LEDs. I have almost finished one brass cantilever and started a second one.

I need to order a 556 IC and IC socket, a few resistors (I may have them somewhere), and a 1 uF capacitor to try the circuit on a scrap of perf board. I don't have a breadboard. I have a handful of cheap old LEDs that I don't need and will use those for testing before spending money on the expensive 1.6 mm LEDs for the final version. I consider these old LEDs disposable, and resistors are dirt cheap and disposable.


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## T-Man (May 16, 2008)

It sounds good.


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## Never Get Old (Apr 16, 2016)

I can't believe that I don't have a half dozen 680kOhm resistors in my box to set the flash rate. I have just about every other value. I'll just add another huge resistor assortment to my ebay cart for $4 since I have to order the ICs and sockets and 1 uF caps anyway. I miss having a neighborhood Radio Shack. Shipping costs make buying small items ridiculously expensive.


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## Never Get Old (Apr 16, 2016)

So, does anyone know how to add this feature to my 12 LED setup above? This addition is beyond my ability.


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## T-Man (May 16, 2008)

All that does is fade out the lamp instead of a quick off. With the size you are dealing with it may not be noticeable.

Years ago I did the calculator. I used a 10uf cap R1 and R2 were 10k and 100k.


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## Never Get Old (Apr 16, 2016)

Others might not notice but I would. The instant on - instant off of LEDs looks odd. I model 1968 - 1982, so the soft on-off of the old incandescent lamps would be nice. This addition would make it the "Rolls Royce" of flasher circuits for complex N scale grade crossings. I assume it could be done with two capacitors and 2 resistors, but the values and where to insert them into the circuit are beyond my ability.

-Never Get Old.


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## Never Get Old (Apr 16, 2016)

Wouldn't it look something like the bottom signal in this diagram?


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## Never Get Old (Apr 16, 2016)

Here is how different old incandescent lamps look compared to instantaneous LEDs. Look how slowly they dim out and they even take some time to ramp up to full brightness. I'd like to recreate this with LEDs.






-Never Get Old-


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## T-Man (May 16, 2008)

Have you considered more than one board? You could build a board for each of the two pairs. The advantage is that if a problem occurs the whole system does not go down. Only a third. If you build just one in my experience, a board may not work and then you have to check all the connections. Being frustrated at times I started a second board then went back, later to see what went wrong.

Years ago I did some fading stuff. One to act like a rotating beacon. Very similar to what you want. 
I will give it a try.


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## T-Man (May 16, 2008)

This is the inital setup. Notice the speed.


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## T-Man (May 16, 2008)

The two sets work.


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## T-Man (May 16, 2008)

To notice the fade the frequency needs to be dropped. So I went with a 10k R1, 100K R2 and 10 uf cap. 40 flashes a minute. The Leds are connected between 555's with reversing current. I believe the 470 ohm resistor on the flasher is the same as the two resistors on the Lamp fader which is one k. The one k is divided into two 150 and 850 with a cap connection in between. So your proposed connection is close but the 150 ohm is located wrong. It should be just one on the opposite side of the 470 resistor where the cap connects on the left. The diodes and the caps are ok.

I understand the need for the two wire feed. 
I guess I do not understand why there are two 555"s? The Lamp circuit can be done with just one.


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## Never Get Old (Apr 16, 2016)

Thanks so much for putting the circuit on the breadboard! At least we know it works fine with 12 LEDs and that I got the initial wiring diagram correct, without the fade effect.

Did you make a video with the fade effect?

My prototype flashed at a rate of 75 to 90 times per minute based on a number of videos. I suppose my choice of 60 was a bit low. I'll aim for 75 when my parts arrive.

I don't know why Rob Paisley used two 555 ICs (or one 556). That would be a question for him. I used that particular circuit because it illustrated two wire operation instead of 3 or 4. Actually, if the mast is used as one conductor, it would be only one wire to run inside the mast. I don't need to go that small in N scale, but people who model in Z scale might. I'll never model Z!

I reduced the circuit to a single 556 IC with an easy point-to-point wiring layout for small circuit boards I have leftover from the days of Radio Shack. The 556 ICs, 1 uF caps, and an assortment of different resistors are on order.

-Never Get Old-


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## T-Man (May 16, 2008)

It does not work or the change is not noticeable. I used a pair of 22uf and then a pair of 100uf. I kept the 470 ohm resistor and added the 150 ohm with the two connections in between.
I may go to with one 555 and try the diagram as is.

This attempt used the 22uf capacitors.


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## T-Man (May 16, 2008)

A radical idea.

These signals are using 10mm LEDs. It must of been for someone since I do not remember the plastic stand. It does have fade.
The flip flop is listed under the Paisley site.
The transistors are 2n2222, the caps are 100uf I will verify that and the resistors.


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## Never Get Old (Apr 16, 2016)

The transistor circuit has a very nice fade effect, but it appears to be a 3-4 wire solution, so that's not going to work in my tiny N scale signals. The point of Rob's circuit is that it uses only 2 wires, and if the mast is used as one conductor, then only one wire.


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## T-Man (May 16, 2008)

If the mast conducts you can use two. The positive was split directly from the 12 volt lead on the board.
The top resistors are 47 k with 470 ohms at the positive end.
The video goes back to 2017.
Could you get fancy and use a double pole signal?
I will take another look at the board but I have no ideas to go forward.


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## Never Get Old (Apr 16, 2016)

The cantilever signals I am building right now have enough room for more wires because I used tubing that was too big, but it's too late now. I'm not making another pair this complicated because its too difficult in N scale. The stanchions are hand hammered brass wire. I have etched brass ladders for the back and brass mesh for the walkway after the LEDs are installed. The LEDs are 1.6 mm, which is close to correct for N scale. I may put the gates and a pair of lights on a second mast as shown.

The other pair of cantilever signals I intend to build, and the flashing crossbucks I intend to build, are going to use much smaller tubing and a single mast. So, a two wire solution is required for those, even though this particular pair can get away with more wiring inside. I wish I had used smaller tubing for this pair, but as I said it's too late now and I'm not doing it over. All future signals will use smaller tubing. I think these will look fine when the ladders, walkways, and crossbuck signs are added.

Concept-wise, it seems like it wouldn't be too difficult to wire a capacitor somewhere in the 555/556 flasher circuit to charge and discharge through the LEDs when the current reverses, but it's beyond my ability to figure it out.











A slightly smaller version of the same cantilever signal:


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## Never Get Old (Apr 16, 2016)

T-Man said:


> It does not work or the change is not noticeable. I used a pair of 22uf and then a pair of 100uf. I kept the 470 ohm resistor and added the 150 ohm with the two connections in between.
> 
> This attempt used the 22uf capacitors.


Could you post a schematic of your circuit please?

-Never Get Old-


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## T-Man (May 16, 2008)

Let me use tiny cad and I will copy out how my board was done. A simple flip flop is easy to find.
They have two capacitors and two transistors and two regulating resistors. Then there is the leds with their resistors.











The circuit as it appears on the board.


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## Never Get Old (Apr 16, 2016)

Thanks, but I have had that circuit for over 30 years in a Radio Shack mini project pamphlet. All that interests me is the dual 555 (or 556) IC 2-wire solution I posted.

I spent some time yesterday using a circuit simulator, and although I could get a soft-on and soft-off effect with the square wave from the IC, it placed a time gap between the two LEDs, which isn't correct.

Online bread board and circuit simulator (free): http://falstad.com/circuit/circuitjs.html

It allows you to draw any circuit you want and test it. Except that their 555 IC simulator is flawed, so I just used a 12 volt square wave input.

-Never Get Old-


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## T-Man (May 16, 2008)

One good thing about using a PCB board is you can install the lights and connect up the board. Eventually change the board out.
I tried adding a cap inline and it turned into a quick flash like you see on a rotational beacon.


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## Never Get Old (Apr 16, 2016)

Could you post the exact schematic that you used for the dual 555 and multiple sets of LEDs (the one that worked in the video) and note where you tried the capacitors that did not give the desired effect? My diagram actually does not work in the circuit simulator.

A circuit simulator is a wonderful thing for those who don't have a bunch of components laying around. I downloaded the offline version of the one I mentioned earlier. Of course, I still don't know how to add the incandescent effect to the 2-wire 555 circuit, but I have had fun anyway. I sure have burned out a lot of capacitors in the simulator! I never pay attention to the polarity, and that's a recipe for disaster.

-Never Get Old-


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## T-Man (May 16, 2008)

I used your diagram. Minus the resistors between the cap and diodes you added. I placed a 150 ohm resistor to the left of the split to those parts.

Now to slow it down replace the 1 uf cap with 10 uf and the 64 k resistor with a 100k.


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## Never Get Old (Apr 16, 2016)

I made some progress but then figured out I had made a 3-wire circuit instead of a 2-wire circuit. Darn!

I have concluded after observing the current flow in my circuit simulator that the incandesent modification cannot be done with 2 wires because it relies on current that is oscillating. 3 wires is the minimum required to add the incandescent feature, which defeats the purpose of the dual 555/single 556 circuit. 

So I have a choice. Put up with 3 wires and have the incandescent feature or use two wires and put up with the instant-on/instant-off of the LEDs.

-Never Get Old-







-Never Get Old-


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## Lemonhawk (Sep 24, 2013)

My solution (which won't work for N scale) would use some LED's from Pololu item #: 2535 (addressable 5mm RGB LED's). Then use the brass tubing as the ground connection to all the LED's and wire the 12v to all LED's and daisy chain the data line to all LED;s and use an Arduino to program them. The ultimate in control - Just too big for N gauge! That would give you realistic dim to bright to dim control and any color you want. Addressable RGB LED's are a lot of fun to paly with and use. Particularly you get great control over the brightness. For those in "Operations" you could set up a "failed Light" scenario and then dispatch a crew to fix it, assuming anyone noticed the failure!


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## Never Get Old (Apr 16, 2016)

I am not interested in soldering to the mast to use it as a conductor because I am using 3D printed targets that melt easily. Although it might be possible to solder and then install the targets, I am using a different approach using just 2 wires running inside.

If anyone is wondering what the incandescent effect looks like, here it is. It is much more natural looking for all but the most modern crossings.








Here is a true 2-wire solution without the incandescent effect. In this solution, I show four masts. Two are short masts with the gate and a pair of lights flashing the opposite direction. The other masts are a pair of over-the-road cantilevers. Due to complexity, I have opted to include only one pair of LEDs over the road facing traffic rather than bi-directional as most prototypes do. Although it is possible to put 4 LEDs at the top of an N scale cantilever, I'm not going to do it for this project.

You can see that at any point there are only two wires inside each mast. I believe this circuit and wiring are the ultimate in simplicity for a 12-LED solution, especially in N scale.














-Never Get Old-


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## Never Get Old (Apr 16, 2016)

This solution is the simplest one I can come up with when using the incandescent appearance modification of the circuit. The two short masts are for the gates and one pair of lights opposing traffic. Unfortunately, they require four wires to keep three left LEDs in series and the three right LEDs in series. Although I probably could accomplish this, 1/16" tubing with 4 wires inside is a pain in the neck. The other two masts are over-the-road cantilevers. They are a bit easier with only three wires, and if I decide to use the mast as a conductor, they could be done with 2 wires and the mast as a conductor. I am not sure but I think I have the left side of the road and the right side of the road correctly wired in parallel, with each running through its own current limiting resistor.

If anyone sees any issues with this circuit or any bad practices or improvements, please let me know. It seems to work in the simulator. The flash rate is 86 flashes per minute with the circuit values shown. The simulation slows down when I record due to limited computer resources, so the video looks a little slow and uneven. It does show the incandescent effect though. Note that non-polarized capacitors must be used in this circuit.








-Never Get Old-


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