I need to make a signal LED flash. Ideas?

Model Railroader Electronics and DCC
1

Hi Everybody

I have three places on my layout where I want to use a signal where I’m approaching a diverging route (facing point) and I want to have my block signal wired with two Logic Rail Signal Animators wired through the Tortoise as shown in this example using the diagram for the 2 head signal:

http://www.logicrailtech.com/sa_inst_supplement5.pdf

Thus when the switch is lined for the main the top head will show clear, the middle and bottom both red. As the train passes over the IR the signal will, of course, drop to red.

If I have the route set for the diverging track the top head will be red and the middle head will be green. This is the one I want to flash because in NYC RR practice a diverging clear signal is flashing, kind of a slow flash, one second+ on—one second+ off. I may force the middle head to stay yellow which would show a diverging approach medium.

Now, the Logic Rail has +5 VDC common anode and sinks the R Y G on the cathode side.

Circuitron makes a BF-3 adjustable rate flasher which would work since the flasher is powered independent of the output voltage but these guys are $25 each and I think I can come up with something less costly.

{from Circuitron catalog, I underlined the output feature}

BF-2 BASIC FLASHER - LAMP (BF-3 is same, but adjustable rate)

The BF-2 is a low cost universal flasher circuit

that will flash any incandescent lamp or Light

Emitting Diode load with a total current draw

of 250 ma. or less. The BF-2 can be powered

by any 8 - 18 volt AC or DC power source.

However, the DC load (lamps or LEDs) applied

to the output may be powered by a different

voltage source

2

I think the easiest thing to do would be to get a flashing LED. Do an Internet search. Someone is bound to have what you are looking for.

You could also do a search for a 555 flasher circuit, but unless you have an electronics junk box, it may be cheaper to just buy the $25 boards.

Another option may be to use the Evan Designs ckt, but use a small relay that turns on the ED ckt with its own power supply. The relay can be activated by the smaller signal voltage.

3

If you just want a flashing LED try this http://www.radioshack.com/5mm-red-blinking-led/2760036.html#.VJhrAP-UAU

4

Thanks Elmer, Mel

Looking at the R-S LED it is 5mm and that is a bit large to fit the signal head. I’d like to use the BLMA 3 color head that has the nano LED already installed so a circuit in the line to the signal head is preferable.

Most of the LEDs with the built in flasher have a much higher flash rate than I’m looking for as well.

I ordered the Circuitron EOT that is made to run from a 3V battery. I’ll experiment with it to see if I can drive it at the 5V output of the Signal Animator, or get a resistor to limit the input to 3V and see if that will work, then clip off the LED and wire it into the signal head lead.

You are right about collecting the components for the flasher circuit. Most of those I found are driven by a 9V or 12V supply.

I may contact Evan Designs and see if they can suggest a flasher similar to what I linked above that will run on 5V.

Thanks for your suggestions, Ed

5

This place has all kinds of 3mm flashing LEDs …

http://led-switch.com/3mm%20LED.htm

Mark.

6

Click on pic’ for info:

Take Care!

Frank

EDIT: Here is the site…clicking pic’, don’t work anymore:

http://www.moreleds.com/3mmredflashing.htm

7

Thanks, Mark and Frank

I have purchased from both of these sellers in the past. I have used the mounted G over R LEDs for dwarf signals. I cut a short piece of black coffee stirer and slip it over the LED for a visor. All Electronics has red over yellow, too. You can extract the LEDs, put the yellow on top and flip it over to make ± and -+, solder the leads together and it makes a quick & easy dwarf to put in-line with a Tortoise.

I bought dozens of bi-color R/G for panel indicators and a bunch of the WW inverted cones for structure lighting! Both are great sources for cheap LEDs.

Quickar makes all sorts of handy electronics kits, too.

That flash rate is good on the LED you pictured, Frank.

Thanks again, Ed

8

If the flashing LEDs are too big - the 555 circuit would be the way to go. Look at Rob Paisley’s site. A 555 chip is like $1.

–Randy

9

Thanks, Randy I’ll look that up. I’d really like to use the BMLA signal heads. They are scale size and there are three nano LEDs in there and they show a “true yellow” color unlike some of the contrived ones that mix red & green.

http://www.blmamodels.com/cgi-bin/webstore/shop.cgi?ud=AwMMBwkKDwUFBxQUEBEcHAYEAwAEAAEFCQkTEQAA&t=main.blue.htm&storeid=1&cols=1&categories=01001-00025&&c=detail.blue.htm&t=main.blue.htm&itemid=4001

Here is a dwarf signal I use made from the inexpensive LEDs from All or the other ebay sellers mentioned above.

In places closer to view I use the Tomar ones but they run about $12 ea. the homemade one is less than a dollar. Actually 25¢

http://www.allelectronics.com/make-a-store/item/led-183/red/yellow-bi-level-led/1.html

Thanks again! Ed

10

The key to look for are things controlled by open collector outputs. You can connect multiple open collector ‘outputs’ together and if multiples get activated at the same time, it won’t hurt anything. This automatically takes care of your ‘logic’ for the green sometimes being on and sometimes flashing. If both the flasher trigger and the solid trigger are open collector, what happens is that if th flashing trigger activates AND the solid trigger activates, the LED will be on solid. The flasher circuit will be blinking away but the solid output being activated will keep the LED on. This is the same thing that DCC decoders do. The ‘output’ lines, white, yellow, green, purple, etc. are all open collector outputs. If you want a light to be on for both forward AND reverse, you can connect both the white and yellow wires to the same light and not worry about programming. Not the best example because it’s usually pretty easy to program a decoder so that the headlights ar enot directional. Say you have a red marker light that you want on when the loco is in reverse OR F3, which you have assigned to the purple wire, is active - all you need to do is connect both the yellow wire and the purple wire to the red light. If F3 is on, the light will be on. If you then put the loco in reverse, the yellow wire will come on too, but it doesn’t matter. Likewise, if F3 is off, and you put the loco in reverse, the yellow wire goes on, so the red light comes on. If you then press F3, the purple wire comes on, but nothing changes and nothing blows up. All because they are open collector ‘outputs’ which really means they are just switches to ground or common. One wire to ground, 2 wires to ground, 3 wires to ground - all the same electrically. And since they are sinks to ground, there’s no ‘source’ feeding from one to the other which could damage a circuit going the other way by feeding power back into a source - which is what happens if you try to test a decoder-equip

11

Thanks again, Randy

I forgot about Rob Paisley’s site and, sure enough one of his basic 555 timer circuits will do just what I want! He even has a calculator for the cap and two resistors so I can get in the ball park with the flash rates (could use a pot, too but I’ll never have to change it once I find the right combo)

I understand what you’re saying about the open collector outputs.

I first ran into these on my old '63 Cadillac! Every courtesy and dome light had one side always hot. You simply ground the other side to neg. through the door jamb switch or some had interior slide switches. Same thing, you had all four doors open there were four paths to ground. Light didn’t go out until last door was closed.

Thanks again for your help. I needed that guidance in the right direction. You were right about the LM555 timer, 75¢ at All Electronics!

Enjoy your Holiday! Ed

12

Ed,

Regarding open collector outputs, please note that depending on the specific “model” of the Signal Animator you have, it may or may not have open collector outputs. The SA-1 (or SA-1-IR) does NOT have open collector outputs; they are “push-pull” which means they are driven both high (~5V when off) and low (~0V when on). The SAD-SBCA (or SAD-SBCA-IR) DOES have open collector outputs (as well as much high current sinking capability - ~150mA per output vs. 20mA per output on the SA-1).

Sincerely,

Chuck

13

Thanks, Chuck

Good to hear from the source! Yes, I’m using the SA-1-IR. Thanks for the info.

I’ll pick up a SAD-SBCA and play around with it since it is better suited to using the flasher circuit I have in mind. I would not have known about that option until you mentioned it. Thanks!

I admire your products, by the way. Keep up the good work!

[edit] as it turns out I just checked my box of Logic Rail inventory and I have a couple of SAD-SBCA-IRs on hand. Great!

Ed

14

The answer is simple. You get a turtle to step on and off of the button. The light will flash. When you are done, you can put the turtle in the soup.

Analog is best.

ROAR