# The Two Transistor Flasher



## T-Man

Error in Red to avoid confusion

Green is added information


This started as a board to use for the 154 Crossing Signal. Hopefuly it will get somewhere.


The Circuit starts here at the WIld Bohemian site

This picture is the corect working diagram with the 10 uf capacitors.











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.


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## T-Man

*Breadboard test video delayed.*

Comimg video of the prototype board.

How To Correctly solder the three legged DEMON the Transistor! UGH!









So it works on nine volts and I used a battery with more charge. It is a small circuit with only pairs of capacitors, LEDs, Transistors, and two pairs of resistors. Now to figure the 2N2222a's for bulbs.


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## gunrunnerjohn

OK, let's see it running the Lionel #154 crossing signal.


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## T-Man

I have a daily double question.

For the2N2222a
The base will have 100ohms, bulb on the collector, To ground on the emitter?

Same for the 555, Bruce said 50 ohms on the base, bulb on the collector and the emmitter to ground. I think they are 14 volt bulbs.

I have both going I started on the 555 timer board tonight. Yeah Right!


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## T-Man

*The next night*

This shows the correct orientation for the 2n3904 Transistor. The ground runs to the right when facing the flat front. The back leg is to the left. The demons are just the blue wire










BUT I used the 2n2222a for giggles and they connect up the opposite way. Forward face is the little square showing. The back leg is to the right.










With this corrected informatiom I built the prototype. Aain.











The new movie.


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## gunrunnerjohn

How well does this work with incandescent bulbs?


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## T-Man

So far it doesn't.

I am finding more with 555 timer circuits. Paisley site has two circuts. One on driving loads greater than 15 volts.The other is a Time Constant Control circuit. I have to check some books too. On this page


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## T-Man

*High Current Crossing Grade Flasher*

The circuit works like a champ. I use a 9 volt Wallart that produces .2 amps at 12 volts. After checking a few all them read a few volts higher than their rating. This is normal since there is is voltage drop when a load is applied.The # 52 bulbs draw .1 amps, the 53 bayonet style bulbs draw .2 amps. Both are 14.4 volts bulbs .So this set works with the 154 crossing signal using a 556 timer which is two 555's in the same chip. 

I plan on using two 555's and I will try to use the 2n2222a's instead of the Darlington's Tip 120's .There is plenty to try out now that I have something that works.

This is easier in a way to get one 555 timer to flash alternately with transistors, it is necessary to have a string of transistors to get the result. That was after viewing a lot of circuits.

The only substitution I made was a 10up capacitor for the 2 uf. I left ouy the adjustable 500k pot . Not a bad circuit. Around 5 resistors two caps and two transistors, Neat.:thumbsup:


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## gunrunnerjohn

The problem with higher current with that circuit is it doesn't have a common ground.

I'd probably use three transistors to drive bulbs, two to actually drive the bulbs, and one to simply serve as an inverter. That way you could have the bulbs returned to common the way they are in a lot of accessories.


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## T-Man

I did notice that!!!!!! when I hooked up the signal. To explain the situation I drew this up.












In the 154 signal two wires go to the light and the frame is common (an AC term for ground). To make it work I had to supply voltage to the frame and each transitor grounded out a bulb. Basically it was wired backwards. I don't think I can place the bulbs on the emitter side, as John so cleverly observed, it has to be inverted to keep the frame common or else a short could occur. 

Now I have to figure that one out.hwell:


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## T-Man

I moved the lamps to the emitter side of the Darlington Transistors. I got common on the signal tower. It works  is it suppose too?


It works so I will play with it. I hope I am not misusing your knowlwdge and dragging you into my project. 

The circuit link fourth down,


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## T-Man

*Try and Fail, Try and Succeed,*

Ok i have a good brightness on the bulbs with the tip 120 Transistor om both sides the emitter and collector. The 2N2222a works better with the bulb on the collector side. Not usable on the emitter side.

Now I want to use two 555's instead of the 556. So the pin numbers are different.

This is the orientation used. The bulb is on the emitter and the 12 volts on the collector. The base has the 1k resistor feed. 










The only way to use the 2N222a's is to invert and use another transistor, which is the stump I am pulling.


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## gunrunnerjohn

That was my suggestion, use one of the 2N2222A's to invert the signal and just drive them both from the common feed. That way you can flash the bulbs and keep a common ground. The reason you can't use the emitter is the emitter-base junction moves around and screws things up, which is why I suggest keeping the emitter grounded. 

I don't see the reason to need two 555's for this, with the inverter in the picture, one square wave gets the alternating flashing job done.


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## T-Man

So far I haven't got two transistors to work together. I have seen circuits that show how to flash with multple transistors. The only thing I have proved is knowing very little about them. The circuits show LEDs flashing but to get a bulb going without specifics, I doubt it will happen. I believe the resistance changes and have no clue what to use. I wouldn't know a inverted circuit if I saw it. Some progress huh!

I have 2n3904's, 2n3906's; and the 2n2222a's. Plus the tip 120's.

I will look again.


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## gunrunnerjohn

Give this a try. This circuit takes a 0-5 volt input square wave and alternately flashes the bulbs. I noticed the 1J, that's supposed to be 1K. All resistors are 1K.


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## T-Man

I like the simplicity. I have looked at so much recently I may have seen it before.

I figure on using pnp transistors to solve the tower Common. I am still looking at the pin 3 output of the 555 and what I can do with transistors. I found plenty of info online.


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