# 154 Crossing Signal



## Dave Sams (Nov 24, 2010)

I got this today at an auction.












$20 (no shipping, free hotdogs )

I would like to wire up an electronic switch to operate the lights rather than use the original track connector.

Does anybody have a resource where I can find, or build something?

(Do I need a "flip flop"?)

Thanks


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## T-Man (May 16, 2008)

The easiest way I know how.


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## Dave Sams (Nov 24, 2010)

That's a cool idea, but I want it to flash while nothing is running.


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## gunrunnerjohn (Nov 10, 2010)

You can probably use a 555 timer and an inverter. Of course, if you want those bulbs to remain, a couple of driver transistors will also probably be required.

What is going to trigger the circuit to start blinking?


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## Dave Sams (Nov 24, 2010)

Right now, I'm thinking of having it running all the time.


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## gunrunnerjohn (Nov 10, 2010)

Well, that wouldn't be all that realistic, but probably pretty easy. Here's a simple flasher circuit, to drive incandescent bulbs, you'd probably have to add a driver transistor for each bulb, I'd probably use some 2N2222A's from my junkbox.


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## Dave Sams (Nov 24, 2010)

gunrunnerjohn said:


> Well, that wouldn't be all that realistic, but probably pretty easy. Here's a simple flasher circuit, to drive incandescent bulbs, you'd probably have to add a driver transistor for each bulb, I'd probably use some 2N2222A's from my junkbox.


Is there supposed to be a diagram?

As far as realistic goes, the accessory is almost twice as tall as my loco

In my little city, we have a short line, and the gates are down and lights flashing all the time, without a train to be seen! It is so bad, arrest warrants have been issued for conductors!

My focus is lots of action, noise and entertainment for little ones.


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## gunrunnerjohn (Nov 10, 2010)

Sorry, forgot the link! 

http://wild-bohemian.com/electronics/flasher.html


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## Dave Sams (Nov 24, 2010)

Thanks

Looks easy enough. 

Where do the "driver transistor" thingys go?


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## gunrunnerjohn (Nov 10, 2010)

You would put them on the output to handle the current.


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## Dave Sams (Nov 24, 2010)

gunrunnerjohn said:


> You would put them on the output to handle the current.


Well of course.

Whew! went right past me.

You got me on that one.

Here is what I found











Looks a little robust to my untrained eye, but what the heck.


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## gunrunnerjohn (Nov 10, 2010)

Well, it'll flash the crossing signal lights, or probably a dozen crossing signal lights!  The 2N3055 is overkill for one lightbulb! 

Truthfully, you could use that same circuit with the 2N2222 transistors for a single signal. It would make the whole package a lot smaller as well. I'm guessing you tune the 39K resistor value to change the flash rate of this circuit...


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## servoguy (Jul 10, 2010)

You can turn off both lights by grounding the bases of both transistors. Do it through a resistor of about 100 ohms to limit the current. You can use transistors like a pair of 2N2222s to ground the bases of the 2N3055. Or you can use a DPST switch or relay. Or you could use an isolated outside rail to provide the ground to the power supply and then the lights would flash whenever anything was making a connection to the isolated rail.

My calculator tells me that the circuit is not going to work very well. The 2N3055s have a maximum current gain of 70 and a minimum current gain of 20. The 39k resistors with a power supply of 20 volts only provide about 0.5 ma of current into the base of the transistors. With a current gain of 70, the transistors will only supply 35 ma of current to the load. It ain't much. Obviously the circuit needs to be redesigned. A simple way to fix it is to add a 2N2222 configured as an emitter follower to increase the current into the base of the 2N3055. You would need a resistor of about 100 ohms between the emitter of the 2N2222 and the base of the 2N3055 to provide 200 ma into the base of the 2N3055 which (at a gain of 50) would provide 10 amps out of the 2N3055. 

The collector of the 2N3055 transistors is connected to the metal can and so the metal can must be isolated from the heat sink. You need to heat sink the 2N3055 transistors as the can dissipate as much as 115 watts. Without the heat sink, their life will be short unless the collector currents are very small. 

The 2N2222 has about the same current gain as the 2N3055, so the base current needs to be increased to drive more than 0.5 ma into the base. The 39k resistor is too big. The 2N2222 collector current can be more than 0.5 amps, so the base current needs to be about 10 ma. That means the 39k resistor is about 20 times too big. If you make the 39k resistor smaller, you have to make the 470u cap larger. 

Personally, I think it would be easier to use a 555 timer and a pair of 2N2222s to drive the lamps.
Bruce Baker


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## Dave Sams (Nov 24, 2010)

It works, but flashes too fast.

I don't understand your reply at all.

There is an error in the parts list. I'm sure you picked up on it.

The RS number is a 3.9k resistor! What a hoot!

All I have to do is slow it down and I'm happy.


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## servoguy (Jul 10, 2010)

If you double the size of the 470u capacitor, you will slow it down by a factor of 2. If you want to slow it down by a factor of 4, you must increase the size of the 470u capacitor by a factor of 4. ETC. To get it slow enough to look realistic, this capacitor is going to get to be quite large which is why I said the circuit is not very well designed. 

You can also slow it down by making the 3.9 k resistor larger, but if you go too large the collector current of the 2N3055 will become too small. You can experiment with the 3.9k resistors, making them larger to get the flash rate you want, and see if the 2N3055s will still drive the lamps.

Here is a data sheet for a 555 timer: http://www.fairchildsemi.com/ds/LM/LM555.pdf Look at the part of the data sheet that deals with astable operation. You can easily change the timing of the circuit by changing the two resistors and the two caps. The output of the 555 then can be used to drive the base (through a resistor of about 50 ohms) of one of the 2N3055s. The collector of this 2N3055 can then drive the base of the other 2N3055 through a resistor of about 200 ohms. Using these values the 2N3055s will drive about 5 amps. Leave the collector and 22 ohm resistor and light bulb as they are.
BB


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## T-Man (May 16, 2008)

GO DAVE GO!!!!!!!

At this point I am going to watch.

No track detection makes it easier.

I found the Rollins site early on and though the graphics are nice, I have had better luck elsewhere. After you tweek it please post it!!!!!


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## Dave Sams (Nov 24, 2010)

Well, the train show today was a bust.

I have more Lionel than they had for sale.

But I stopped by the ole Radio Shack and picked up a few more capacitors.








The two 470mfd capacitors were increased to 3470mfd.

Now all I need are some new painted #53 bulbs and I'll be in great shape.

Thanks to all for the tips and encouragement.


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## gunrunnerjohn (Nov 10, 2010)

If you drop into your hobby shop, you can buy clear acrylic paint and dip your bulbs, much cheaper than buying the colored ones.


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## Dave Sams (Nov 24, 2010)

gunrunnerjohn said:


> If you drop into your hobby shop, you can buy clear acrylic paint and dip your bulbs, much cheaper than buying the colored ones.


I haven't tried dipping bulbs in acrylic paint. 

Does it leave uniform color?

Painted bulbs are only $.20 each more, how much is the paint?


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## gunrunnerjohn (Nov 10, 2010)

I bought a jar of it for around $2, it'll do a lot of bulbs. Mine came out fine.


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## T-Man (May 16, 2008)

I went throught this and I am still not sure what was done, or added or diagram that was used from the start? A lot of neat ideas but the final outcome?

Transistors are fun but I haven't used many to date.


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## Dave Sams (Nov 24, 2010)

T-Man

I used the diagram from my earlier post but increased the 470mfd caps to 3470mfd. Also the 39k resistor part number was incorrect in the parts list.

The result is the second video with the lights flashing at a slower rate.

At 3470mfd, I can run three crossing signals at once. I added a fourth, and somthing got hot. No problem for me, I'm building a second board to have signals flashing at different times. (I'm working on another crossing which will post later.)

There probably is a cheaper way, and there probably is a way to change some of the resistors, but it works.

Since completing the project, I did a search and found some other ways to create the flip flop. And, I found a Lionel crossing signal which has a flip flop circuilt in the base, but they are about $10 each.

Bottom line, it works, I got the look I wanted, nothing under the table smokes.....I'm happy.


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## T-Man (May 16, 2008)

Thanks! The variations interests me and I would like a good transistor circuit to build and show. I have to study this a little more.


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## T-Man (May 16, 2008)

I have been bitten by the electronic bug. FLashers, FLickers, Welders.Plus I organized my electronic parts. Yesterday I got a maling of transistors that I want to try for flashing and switching bulbs so expect to see more.I will squeek if I have any questions.


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## Dave Sams (Nov 24, 2010)

Great! Keep us posted.

I would like to build a welding simulator. I purcahsed one and was very disappointed. It just looked like a blinking blue light. I e mailed the manufacturere, they said they would look into it, and that was it. I returned it since it did nothing like the web site indicated.


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## T-Man (May 16, 2008)

You must of seen my welding circuit thread. What do you think?

I breaded the wild bohemian transistor flasher and susbstituted some capacitors, movie is coming.


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## T-Man (May 16, 2008)

ERROR Will Robinson ERROR

I have had to back track a little. In the original ciruit a 10 uf capacitor was used . Well That is correct so my suggestions for using others are out the window.

The cause, installing the transistor backwards. We can talk all night about emmitters and collectors but ifth T-man don't do it right, it is wrong.

I goofed in identifyng the correct side of the transistor. This picture they are in backwards even the movie is wrong. SO be warned.











This is what I came up with. 2N3904 transistors and 68 uf capacitors, The 10 uf suggested were too fast so I had some 68's because I am saving my 100 ufs caps. This is on nine volts. I kept it simple and it is small. That is a 5 by 7 cm board.

I am going to take this to the Technical Forum and play with it. The Thread will be a Two Transistor Flasher.


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## T-Man (May 16, 2008)

This is the replacemnent 
You can hardly tell the difference.

Much brighter !!!!


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## T-Man (May 16, 2008)

Another option is with a 555 timer I found this page and like the fifth circuit for driving lamps. It uses two darlingtons npn's


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## gunrunnerjohn (Nov 10, 2010)

You ain't kidding *High Current*, 2 amp bulbs!


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## T-Man (May 16, 2008)

The 2n2222a have let me down. They won't light a 12 lamp. They work with LEDs on the flasher circuit but that is it. The 2n3904 did light a 12 volt pin lamp with a little heat too, from a nine volt battery. I fiddled with it, used 100 ohms on the base. So far it is the only diagram that I know works. I have a vast area of bits and pieces, three books, 4 mags, notes and internet.

The Tony Van Roon site moved to this.


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## gunrunnerjohn (Nov 10, 2010)

Uhh... the 2N2222 will certainly light a lamp if you have a correct circuit, they handle hundreds of milliamps with ease. Exactly how are you attempting to use it? Note that you need to take account of the current gain of a transistor when you use it. Typically, you will get something like 50-60 for a current gain for the 2N2222A, so to light a 200MA lamp, you're going to have to supply 4MA base current from the driver.


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## T-Man (May 16, 2008)

Well the 555 does just that, so it may be some tinkering. But to get two to flasher a 556 is needed. And that takes you to this thread of two transistors.

So Dave we got two ways to flash the crossing signal now. The next step is to figure out a good track detector. I am currnetly looking at an AC version that may work.


Number four on this link.


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## gunrunnerjohn (Nov 10, 2010)

This one is dependent on measuring some current draw, but it does drop .7 volts across those big diodes. To minimize the drop, I'd be thinking of using Schottky diodes and adjusting the resistor values. That will get the drop down to about .3 volts.


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## T-Man (May 16, 2008)

What amperage should I be looking for????

It's the first time I have heard of those.


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## Dave Sams (Nov 24, 2010)

T-Man said:


> Well the 555 does just that, so it may be some tinkering. But to get two to flasher a 556 is needed. And that takes you to this thread of two transistors.
> 
> So Dave we got two ways to flash the crossing signal now. The next step is to figure out a good track detector. I am currnetly looking at an AC version that may work.
> 
> ...


NICE

I don't have anything activate my crossing signals. They blink whenever the table is alive.

Some may say it doesn't look realistic, but many times I'm at a crossing with the lights flashing, waiting for the train.

Also, for me, it adds motion and interest to the table. I had a visitor complement my set up recently. She said, "I don't know where to look!"

Mission accomplished.


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## gunrunnerjohn (Nov 10, 2010)

Here's some 5A Schottky Diodes which might do the trick.


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