Emergency Led Flasher

I am looking to make a simple reverse light flasher that flashes the reverse lights alternately at a fast rate EXAMPLE: right reverse flashes twice the left reverse flashes twice then repeat

or

I would like to build a programmable flasher where i could adjust flash speed and amount of flashes between two/four light outputs independently but i think that may be a bit hard for me at the moment

This will be flashing reverse lights with LEDs in them so the current draw is minimal.

thanks in advanced

There are a few problems with what you're planning on doing.

1) If you modify your vehicles' lighting system, it may not pass a safety inspection. It doesn't matter whether or not your state conducts annual safety inspections, as a law enforcement officer may decide to conduct one at an inopportune time.

2) Your backup lights are there for a reason. If they don't function when you're backing up ...

3) LEDs, even those claimed "super bright", are probably not bright enough for what you want to do. Also, you would have to ensure that they were properly focused into the reflector to get the best possible coverage. This would be awkward to do with typical standard or superbright LEDs.

4) Standard incandescent bulbs of the type normally used for backup lamps won't be very effective if you try to cycle them quickly.

5) Emergency vehicles and road crews use lighting systems that have Xenon flash tubes in them. These require high voltage to fire, which is generated using an oscillator circuit driving a transformer and rectifier. There are kits available online at reasonable prices that you can simply drill a few holes in your taillamp housings and install. It would likely cost you more to build one yourself than you can buy a complete kit for. I bought a couple of kits a few years ago at a national chain auto parts store for $35 each, one for the front and one for the rear.

6) Check your state and local laws as to what colors are permissable for you to use. In most states, even having blue lights installed on a non-law-enforcement vehicle will prompt a LEO to pull you over and cite you; and it doesn't matter if they are off or non-functional. You might be OK using white or yellow, but you should still check.

1) Safety inspection is not an issue as all my normal lighting will not change
2)Reverse lights will only be isolated when flashers are on
3) The LEDs are 921 replacement bulbs that i am using in the reverse light housing( they are plenty bright )
4) Using LEDs
5)i would like to use an existing lights and most of the new emergency lighting is now LED
6)Use is only for show and will only be using white light

OK, I had to run all of that by you first to make sure you weren't going to get yourself in hot water.

What kind of current do these replacement 921 bulbs require?

Is the current constant, or is there an initial surge?

Do you have access to both the power and ground side of the sockets? The reason I'm asking is because it's usually easier to sink current (provide a ground) than to source it (provide 12v), and sometimes it's difficult or impossible to isolate the ground circuit depending upon the construction of the socket.

each bulb has 9 80ma leds so its about 800ma per bulb constant

I have access to both power and ground

OK, and each LED bulb is rated at 12V? I'm asking because the 80mA rating sounds close to some individual super-bright LED's that are rated at that current at around 3.6V. It's likely that several of them could be wired in series internally. with nine 80mA superbright LED's in a 12V circuit, I'd expect three strings of three in series. If you can see a single resistor, or three resistors, that'll be a big clue.

See the attached schematic.

Ignore "CMD1", that's just a Spice directive.

How it works:
Most of the circuit consists of CMOS IC's.

The square wave oscillator is a 4093 Schmitt-trigger 2-input NAND gate. The combination of R1, R2, and C1 set the frequency of the oscillator. R2, the 10K resistor, is necessary to prevent overloading the output of the gate in case R1 is set too low. If you change C1 to a value of 2.2uF, you'll have a range of about 3 complete cycles per second to one complete cycle every 3 seconds.

The square waves are used as a clock for the 4017, a 5-stage Johnson counter. D0 starts out being 1, the remaining D1 through D9 are zero. As the clock progresses, the 1 moves up to D1, and continues moving each time another clock pulse is received. When D9 is a 1 and a clock pulse is received, D9 becomes zero and D0 becomes 1.

Outputs D0, D2, and D4 are ORed together to generate a series of three pulses. D5, D7, and D9 are ORed together to generate a separate series of 3 pulses. These pulses are fed via 10K Ohm resistors to the gates of power MOSFETs, which provide switched grounds to the LED's. In the schematic, one of your LED "bulb" assemblies is depicted as three LED's and one resistor.

I am new so bare with me...........

I understand eveything but these three things

U1a
U3a
U3B

Also the 1.6V .ID i am lost on or is that part of the cmd1 thing i am to ignore

OK, those are "reference designators"

U1, R3, C4... etc are for shorthand reference in the designs. "U" is a common prefix for an integrated circuit, "R" is for resistors, "C" is for capacitors.

After the prefix comes the sequence number, ie: U1, U2, U3... to indicate different integrated circuits (or "IC" as they're commonly referred to in shorthand.

Logic ICs frequently have a number of functionally identical yet independent sub-circuits, or "gates". These can be indicated by a letter suffix for the IC number.

So, "U2B" would be the 2nd gate of the 2nd IC.
U3A is the 1st gate of the 3rd IC.

Make sense?

ok, it makes sence now
even more so when i looked up what 4093 was

Are you familar with digi-key?
could you possible help me make a quick list of what to order

I'm familiar with Digi-key, but the ordering is pretty much up to you

I've thrown together a BOM for the circuit. It doesn't include a circuit board, of course.
You can actually pick all of this stuff up from your local Radio Shack, including a generic circuit board. You'll pay a tad more, but you'll save on shipping. Oops, not true - they don't carry CMOS IC's anymore Well, you just need the IC's from Digi-Key then. But as long as you're ordering those... might as well get it all.

Attributes "RAD" means radial (both leads coming out one end) and "AXIAL" means one lead each end. You can just get everything axial; easier to deal with.

Many manufacturers use "CD" as a prefix for standard CMOS components. And usually, an "N" suffix means a DIP package (dual inline pins). DIP is an old standard, but it's the easiest for a hobbiest to use.

Digi-key doesn't stock the 4017 in CMOS; they only have it in a TTL/CMOS version which is restricted to 4.75-5.25 volts. That won't work for you. One of the big reasons I went with CMOS is that you wouldn't need a voltage regulator circuit to get it down to 5V. Besides, I don't recalling TTL (74 series IC's) having a Johnson counter offhand - perhaps there is one, but making a clock circuit wouldn't be quite as easy. Let me check elsewhere.

ok thanks for all the great help

Here you go. Head over to Mouser.com and order these. They're so cheap, you might as well order an extra one of each for spares.
You can pick up an experimenter's circuit board over at Radio Shack for a couple bucks. A project box would be a good idea, too.

I re-drew the schematic using a different program; this is what your finished project should be wired like. There is also a suggested board layout. My components library didn't have a pot just like the one you're getting, but that's OK, it's close enough The board in the drawing measures 3.2" x 1.8", but Radio Shack has a board, catalog # 276-149 that measures 1 7/8" x 2 7/8" that will work just fine for this.

You don't have to lay the IRF510's down, they can stick up out of the board. Just make sure the tabs won't touch anything that's either hot (12V) or ground, or the circuit won't work properly.

I just ordered everything, I did not expect it to be so cheap

Thanks for all the help i did not expect a complete layout and all

I will get it finished soon and let you know when everything works

thanks

This is great, led flashers are so expensive. Now I can try and make my own. Does any body have any idea on how to make flash patterns? I'm a firefighter and I kinda want more than one setting.

Hi Frylock,

Well, the circuit is fairly well-explained in the diagram itself as to what it does.

The 4017 counter is kind of the key to the circuit; it's outputs are all low except for one of them which is high. As it receives clock pulses, the high moves from O0 to O9, then back to O0. Those ten outputs can be connected in a myriad of ways to other gates, etc.

However, with microcontrollers being so cheap nowadays, it might be better to explore that route than start adding more gates to this circuit. With a programmable microcontroller you could have an extreme amount of flexibility - and basically all you would need would be the controller, power supply, and output MOSFETs - that's if you get a CMOS controller capable of running on 14V.

Built the circuit and tried it and nothing happens.
I went over the entire thing and even did a check to see if i had any bad wires

A LED will light if i ground the other ground output from the irf510 but that is it.

Utoh - did you observe precautions for static sensitive devices?

I forget to mention this, because Florida is so humid that static is hardly ever a problem.

CMOS circuits are great, very low power, but they are also very sensitive to static discharge. If where you are has very low humidity, static will be a big problem. You should be using an ESD-safe work area. You could make one cheaply by just taking a sheet of aluminum foil and wrap it around a piece of cardboard. Ground the foil to an electrical outlet's ground. Touch the foil before touching your parts. Leave the parts in the static bag until you've put it on the foil.

However, you've come this far, so time to troubleshoot.

Remove the connection from one of the MOSFET's gates. Connect 12v power and ground to the board, and one of your LED's to the output. Place 12V on the gate; your LED should light. Place ground on the gate; the LED should turn off.