I would like to build some circuits to activate crossing signals and also a circuit to do the alternate flashing of the LEDs in the crossing signals. I am not very skilled in building electronic circuits although I have had success with the few I've tried. I recently was given an old issue of OGR in which a writer commented on an article in Run 148 "How to use Flashing LEDs on Your Layout". Does anyone in this Forum have any info for projects like these?
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.)
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.
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.
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.
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?
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.
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.
Another fine product of the Cleveland Public School system.
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.
William Pickert "A day without trains is a day wasted"
I have built this circuit on a test board and it works fine, I did find it to flash a little fast and as your suggestion I increased the values of R1 & R2 and this gave me a more pleasing flash speed. I have also ordered the book that was recommended on this forum and am looking forward to trying some things out of it.
Thank you again and thanks to all who responded
Originally Posted by gunrunnerjohn:
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...
"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.
Arthur P. Bloom TCA 86-23906 "I love the smell of smoke pellets in the morning!"
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?
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
Another fine product of the Cleveland Public School system.
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.
Above is a schematic from my notebook for light bulbs. It should work LEDs with a proper resistor. I have not tried it to verify it works. If you click on the bottom photo they come up larger and more readable.
Below is a repeat cycle schematic which works a relay. If the flash rate is not too fast the relay contacts can flash LEDs or bulbs and switch large loads. A cool effect is to use capacitor discharge into the bulbs or LEDs. Depending on the capacitance used the bulbs or LEDs will appear bright and slowly fade between flashes. It can flash bulbs alternately or a single string of bulbs on and off. The cycle does not have to be 50-50 but can be. Instead of a relay a transistor could be used I think. I have made this circuit but avoid work at the chip level now if possible..
Radio Shack makes a board which is very useful and accommodates 2, 8 pin chips like the 555. Solder in a socket first then plug in the chip. Makes assembly very easy. For input voltage use a 7812 regulator circuit shown in the first diagram.