Building Flasher Circuit

Save yourself a whole lot of trouble by going to Dalee Electronics. They have built up flasher circuits that will operate either regular bulbs or LEDs. They are reasonably priced as well. (No, I don't work for them, just like and use their stuff.)

Chris

LVHR

I'll put in a plug for Evans Designs as well, they sell some interesting LED systems. For the alternating flashing lights on a crossbar a 455 timer would be easy enough (and adjustable).

If you can't find what you want, email me and I'll get back to you with a circuit.

If you like the challange of "building your own", as opposed to buying a circuit preassembled, look for a book titled "Easy Electronics Projects For Toy Trains" by David E Greenwald.  It has exactly what you are looking for.

Check this page: Model RR Electronic Circuits

Here is the Dual Alternating Flasher Circuit that will do the flashing lights.  It uses power transistors that will flash almost anything, you could also use smaller transistors for a single bulb in the dual signals.  I suspect the 2N3055's would probably drive half a dozen signals.

Here is the IR Train Detector that you can build to detect the presence of a train.

Here's a board from WEHONEST on eBay.  IR/Magnetic Presence Detector

I bought some of these, they come with IR and reed switches so you can do block detection using IR or a magnet in your trains.  The magnetic option is good if you only want a specific train or two to activate the signal or other device.

Thanks gunrunnerjohn,

Yes, I do enjoy trying these building projects. These will be intersting for me to try. One question, and with your backround this may be simple for you to answer, can the flasher timing be made adjustable by adding or changing a component?

Thanks

Ray 

Yep, change the 470uF cap value to change the flash rate.  Changing the 39K resistor would also change the flash rate.  I haven't tried that circuit, but it sure is simple enough.

Note that the lamps are part of the circuit, so this one won't run without the lamps in place.  It's also not really suitable for LED use, it was designed for incandescent lamps.  There are many other similar circuits using the NE555 that will work for LED signals.

I dug this out of the archives, from about 30-35 years ago.

Bill

Looks very similar to the previous one I posted, just uses more parts.

Get an NE555 from Radio Shack.There is a simple formula

for what resistor and capacitor values to use for the frequency

of flashing you want. Picking resistor values will get a

square wave output and both LEDs can be driven directly from

the 555 output.

All Electronics sells a $5 kit that flashes 2 red LED's.  The kit is currently on backorder but should be available at the end of July.   Here's the link"

http://www.allelectronics.com/...D-FLASHER-KIT/1.html

Check out Rainbowkits.com.   They have an assortment of electronic kits, including the Blinkey for $3.95.  Also sell LEDs in quantity and resistors $1.50 for a Pack of 100.

This is a simple 555 circuit. Might also work with light bulbs. See the PDF schematic on the site. Power it with a 7812 regulator circuit for bulbs or a 7809 etc. for LEDs.

I have a circuit in my note book which is a little bit different,does the same thing. An alternative is to use a single flasher and power a relay coil instead,then power the bulbs with capacitor discharge with the contacts. Gives a cool flashing effect for light bulbs.

Dale H

The "blinkey" kit only has one "flaw"--- the leds will not be on for the same time-- the circuit as built will have one led on for 1/3 the other on for 2/3 of a cycle. Real crossing warning lights use a 50% duty cycle. To fix this circuit to generate a 50% duty cycle, all that needs to be added is a 1N4148/1N914 diode across the R2 resistor. The cathode(the end marked with a band) of the diode must be connected to  the cap/resistor junction.

 The Diode in effect shorts out the R2 resistor during the IC's charge time, and as long as the R1 and R2 are the same value, you will get a 50% duty cycle.

The resistors are not the same value.  I think you could accomplish the same thing by adjusting the values of the resistors and/or caps.  I haven't put this together to see...

This one looks pretty flexible, it has pots to adjust each LED flash rate.

For a square wave output, make R1 much smaller than R2.

Set R1 to 10K then with R2 = to 2.2 Meg and C= to .1

each LED will be on for .15 sec. If you want to change

the flashing rate use the formula t=.693* R2 *C with R1

mush smaller than R2.

For a crossing flasher, I'd probably bump the times up around 5-10 x over the .15 you mention.

Hey to all you folks,

I have no excuse now not to get one of these going, as a matter of fact I want to try a couple different circuits to see which I would prefer.

Thanks for all the replies, this OGR is a great place to be

Ray

Success stories are always the best news.

The flashing circuit from Rainbowkits is very useful.

The formula for the output being high is .693(R1+R2)*C

and for the output being low is .693*R2*C.

If R1 is much smaller than R2 than the output

will be a square wave with equal on/off times

of the LEDs with a period of .693*2*R2*C.

I recently ran across a 555 circuit like John's, except it had a 2Q2222 transistor in place of R3, R4. The transistor was connected to one LED. What's the purpose of it?

Chris

LVHR

Without seeing the actual circuit, it's hard to tell.  I'd suspect it was for a higher current output.

Can you post the schematic?

For those of you looking to build a single LED flasher, there are LED's available with the flasher built in. Just hook it up to DC and it flashes.

John,

Sorry for the delay. Here is the circuit. The other question Ihave is how to connect the LEDs. I want 8, all to flash at the same time. Would 1 or 2 be the better way to wire these?

Thanks,

Chris

LVHR

"The "blinkey" kit only has one "flaw"--- the leds will not be on for the same time-- the circuit as built will have one led on for 1/3 the other on for 2/3 of a cycle. Real crossing warning lights use a 50% duty cycle."

Not all crossing signals are that exact. There are many around here that have a duty cycle that is far from a perfect 50/50. Some, in fact, are so far off that you can hardly see the shorter flashes. Of course, we are talking about the LIRR, not a real railroad.

You can get by with diagram 2 maybe if you increase input to 12VDC. Use a 7812 regulating circuit as input. White LEDs have about 3 volts forward, red ones about 2 volts and use normally 20 ma. Size resistor accordingly. Resistor value in ohms equals 12 volts minus the number of LEDs in series times their voltage drop all divided by .02. If 0 use a 1 ohm resistor 

Dale H

One change, I tend to avoid putting LED's in parallel without individual current limiting resistors.  Series is fine, but in parallel they will sometimes have different currents through the individual LED.  I suspect more than one in series may mitigate this issue somewhat, but I've never really researched it.

I don't like this circuit!  It would be better to have the 270 ohm resistor, LED and transistor all in series so that the LED is turned ON by the transistor.  As it is, the transistor must turn OFF the LED by shunting current away from the LED.  As shown, there would be 33 mA and .3 watts of dissipation in the resistor when the LED is OFF.  This problem will get much worse if you have multiple LEDs in series since the resistor will have a much smaller value, greatly increasing the current in the transistor when it is shunting the current away from the LEDs.

What is the purpose of the transister,the 555 can output 100ma

directly.

Dale,

Could you retake the photos or do a scan of the circuits you posted and maybe add the listof components? I can't quite make them out.

Thanks

Ray

Double click on the photo & it will enlarge.

Ken