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How can i make a circuit to flash alternating LED bulbs? Answered

Here's what im looking to do: i want to set up my plow truck with tow-truck lights, like i've seen on "Operation Repo". Each of the 4 marker lights would have about 10 LED's housed inside the lens, and they would alternate flashes. opposite corners would flash at the same time, and the 2 pairs would alternate in a AA-BB-AA-BB-AA-BB-AA-BB fashion. its a vehicle, so i would obviously want it to run off of 12vDC. the circuit needs to be controlled with a simple "On-Off" toggle switch. the circuit also needs to be simple, and fairly inexpensive. i can BUILD any circuit you want, but i really have no idea what im doing when it comes to designing.

Long story short, here's what i need:
-12vDC feed
-toggle switch
-40 LEDs, split into 2 alternating groups
-budget build

i KNOW someone out there can do this crap in their sleep, and help would be greatly appreciated. ive looked all over, and cant seem to find a schematic or anything close enough to be adapted.

just to be clear... im looking for a strobe effect, moreso than a slow blink. the truck has blinkers... im looking for attention-getting strobes


Try this circuit: http://www.talkingelectronics.com/projects/30%20LED%20Projects/30%20LED%20Projects.html#55

Theres 3 circuits there, but they all use 4 LEDs, you would replace the single LED for a 2 chains of 5 in series, then in paralell. You'd have to figure out the LED resistor value, but this circuit should fit your needs. :)


I'd use the one with the 555 and the 4017, with Q0 and 1 going to the first transistor via the resistors, then Q2 and 3 to the 2nd one. Then connect Q4 to Reset.


6 years ago

Here is a single IC running 20 / 20 LEDs on 12 VDC

Don't try it with White LEDs and careful not to exceed 15 VDC ever ! !


12V- complimentry556.png

whats wrong with white LED's? thats probably what i would want to use

Red leds use 2.2VDC and White leds use 3.6VDC ...
Four red in series is 8.8VDC ( 12 - 8.8 ) = 3.2 to regulate.
Four white in series is 14.4VDC is more then you can light with your battery.
Three white in series is 10.8VDC ( 12 - 10.8 ) = 1.2VDC
most leds run on 20ma that makes the series resistor 60 ohms.
You will need 7 groups of three for a total of 21 leds each way.
Seven groups of 20 ma each loads the timers ( 7 x .02 ) = 0.14ADC
or 140 ma well below the 300 ma capacity of the timers.


i would alter the LED chains to fit my conditions, but i like this. i suppose it would be difficult to get 2 blinks before it switches to the other LED chain? im intrigued by this LM556 IC though... it's 2 timers in one? thats pretty cool

I started out by writing several paragraphs describing what you could build, using a turn-signal flasher, relays, and a multipole (3PST) switch.

Then I went to Google and typed in "alternating flasher circuit" (which is what you should have done up front). You can do that yourself, and scroll through the results. Or, you could look at this result, http://www.warningsystems.com.au/flashers.htm, and see if it's more efficient for you to just buy a black box already set up for an automotive application.

pardon me sir... but if you read my post, you would see that i HAVE searched google and varous forums.

"ive looked all over, and cant seem to find a schematic or anything close enough to be adapted."

if you wont provide help, just leave rather than telling me its my problem to worry about and that i havent done this or that blah blah blah....

I did help. The search term I provided includes links to multiple schematics, as well as to the enclosed solution.

question: do you understand that im looking for a strobeish sortof effect? "alternating flashers" are like school bus lights. i have a set of blinkers... and 4-ways....

No, that was not clear from your topic text. What you described sounded like wanting doubled-up turn signals, which is what I referenced. If you want strobe flashers, you could get those by inserting a strobe trigger on each output of the flasher control I cited.

You do need to be a bit careful, however. There are both national and local regulations regarding vehicle lights, especially around lights which can appear to mimic emergency vehicles. If you're going to be driving on-road, then you need to ensure that your vehicle is properly licensed for emergency lights (the fines for "impersonation" can be as high as those for DUIs).

well... its for a plow that i run inside a private community, so as far as i'm concerned.. the legal aspect is no matter. i DO appreciate your input, despite my slight misunderstanding/annoyance/unclearness. using a strobe trigger sounds kind of like using a "flip flop" to control strobe lights, correct?

A flip flop is probably the best solution to get alternating lights. Seeing as you have quite a few LEDs, you may need to put a relay in so the flasher circuit itself does not have to deal with the full current.

There are a lot of circuit diagrams available, just pick one intended to work at somewhere near 12V, and swap the transistors for ones with a high enough current capability.

Also, what are the voltage/current ratings for the LEDs,?

hey, this is probably the simplest "flip flop" i saw. its from wikipedia, the trusted information site -.-
anyways... when you look at this schematic, i dont know what the A and E stand for. are they like the outputs? also... what resistor values would i need to use this with 12v? or atleast what do i need to do to figure it out?

Flip Flop.png

i dont have specific LED's picked out, but if i would go this route i would have to so i know the transistor's rating that i need

MAYBE i should combine different circuits? use a straight-up "flip flop" to control 2 separate strobe lights?