OK, if you're going to be using those "superbright" high-current multileg LED critters, they generally draw around 70mA @ 3.4-3.9V, depending upon the color you choose (different colors have different chemistry in the PN junction, thus emit different frequency light, and require different voltage levels; blue and white LEDs tend to be higher voltage than the rest.)

So, let's say you were using white LEDs rated for 70mA @ 3.9V
14V / 3.9 = 3.58+
So, three in series
Limiting resistor:
E = 14V - (3 x 3.9)
E = 14 - 11.7
E = 2.3
OK, now let's get 70mA across 2.3V:
R = E / I
R = 2.3 / 70mA
R = 2.3 / .07
R = 32.85 Ohms
Closest resistor is (conveniently!) 33 Ohms
But now we're starting to get some serious current through our resistor - better check to see what the wattage requirement is:
P = E x I
P = 2.3 x .07
P = 0.161 Watts
You'll need to use 1/4 Watt or higher rated resistors.

Ok, so 3 per string @ 70mA.
5.6A / 0.07 = 80 strings of 3, or 240 LEDs. While a properly heat-sinked IRF510 would work, it might tend towards a bit marginal. After all, why use a 2x4 when a 10x12 will work just fine? An IRF3703 is the same physical size as the IRF510, yet will handle up to around 1000 of these 3-LED strings (proper heat-sinking applies)

 

5.6A / 0.07 = 80 strings of 3, or 240 LEDs. While a properly heat-sinked IRF510 would work, it might tend towards a bit marginal. After all, why use a 2x4 when a 10x12 will work just fine? An IRF3703 is the same physical size as the IRF510, yet will handle up to around 1000 of these 3-LED strings (proper heat-sinking applies)

To be honest, I hadn't quite made a final decision yet on whether I was going to use the high-output 4-pin LEDs, or the 2-pin 10mm ones.. (Although from what I hear the power requirements are pretty similar either way)

From looking at mauser it seems the big issue would be cost... The IRF510s run about a buck each, whereas the IRF3703 is almost 5... Between 2 of those, plus the cost of the other components, that's ALMOST to the point where I might as well spend the $30ish for a pre-made commercial LED flasher unit from one of the emergency supply companies, that would have umpteen different flash patterns to choose from anyway.. So I guess this circuit (with the 510s) would be good for smaller applications, but not larger ones... Good to know at least.

 

Heya again SgtWookie... I'm in the process of ordering my parts for this project, but came up with a snag... Those lovely little MOSFETs are on backorder.. (Almost 3500 of 'em!)

I know you had mentioned the 3703 as a replacement, but as I said before the cost almost makes it not worth it... I noticed that they do have a large stock of the 510 in the non-RoHS compliant model... Would this work, or should I stay away from the non-compliant ones? Thanks again for all the help!

 

Hi again, Chikan!

Well, I had originally specified the IRF510 because you can even get them at a Radio Shack, if you don't mind paying extra for the convenience.

Actually, any of the higher-numbered IRF5xx would work better, because they have a lower Rds(on) than the IRF510.

You can also use the IRFZ14, IRFZ20, IRFZ24, IRFZ34, etc. which are actually a much better match for this application. They're for lower voltages than the IRF5xx series, but have a lower Rds(on), so can carry more current.

Basically what you're looking for is an N-channel power MOSFET with a Vdss >16v, low Rds(on), Vgs of at least +/-15v, and Id sufficient to carry your load.

Here's an E-bay auction for 10 IRFZ20 MOSFETs, $8.94 delivered.
http://cgi.ebay.com/IRFZ20-IRFZ-20-...eZWD1VQQtrksidZp1638.m118.l1247QQcmdZViewItem
I've bought from them before. They combine shipping favorably. But unless you're building 5 of these flashers, you'll wind up with extras. What to do, what to do...

Remember, you can connect power MOSFETS in parallel to increase load carrying capabilities without having to do anything special like you have to do for transistors. However, you'll probably find it less expensive to just buy one rated high enough for your needs.

Don't worry about the RoHS compliance unless you're going to be making large numbers of these for commercial/retail use.

Basically, RoHS compliant parts are made without lead, and do not contain certain chemical compounds that are on a restricted list that may be harmful to humans or the environment. RoHS compliance is currently a requirement of electronic/electrical manufacturers in the EU, and the US is heading that way. But for home use, I'm not ready to give up my 63/37 SnPb solder just yet.

 

Ok cool, thanks for the info Sgt.. (again.. lol)

For the time being, I just ordered the non-compliant ones... I'm only making 2 or 3 of these things, so I don't need a huge supply.. I went ahead and just ordered the non-compliant ones... They were only a few cents different in cost..

I ordered my LEDs and other supplies a couple days ago, so hopefully I'll have these things running in the next couple weeks..

On a side note, I had a hypothetical question about this circuit... If I were to add more MOSFET/resistor/LED arrays in there, how difficult would it be to change this to a chaser type of display? The guy I'm building this for is considering putting one of those LED traffic arrows in his rear windshield, but the commercial ones cost upwards of $500... I'm sure this would probably be an easier circuit to do using PICs since they normally have multiple flash patterns, but I don't know how to program them, nor do I have the necessary stuff to do so.. As I said though, he's just kinda curious about adding this.. I'm hoping I can convince him that the lights I'm already building will be enough.. LOL

Thanks again!

 

On a side note, I had a hypothetical question about this circuit... If I were to add more MOSFET/resistor/LED arrays in there, how difficult would it be to change this to a chaser type of display? The guy I'm building this for is considering putting one of those LED traffic arrows in his rear windshield, but the commercial ones cost upwards of $500... I'm sure this would probably be an easier circuit to do using PICs since they normally have multiple flash patterns, but I don't know how to program them, nor do I have the necessary stuff to do so.. As I said though, he's just kinda curious about adding this.. I'm hoping I can convince him that the lights I'm already building will be enough.. LOL

Thanks again!

Sure, no problem

Well, the 4017 is a good basic candidate for a chaser, or "moving arrow" type display.

You wouldn't even need extra gates, just as many power MOSFETS to sink the current from the LED's, and you're almost done

The 1st power MOSFET you'd connect to D0,
The 2nd power MOSFET you'd connect to D1, etc...
and when you figured you had enough progressive elements for the moving arrow, if you haven't gone through all 10 Dn outputs, just connect the 1st unused output to the RESET input (after disconnecting it from ground first, of course!)

That's it!

 

Sure, no problem

Well, the 4017 is a good basic candidate for a chaser, or "moving arrow" type display.

You wouldn't even need extra gates, just as many power MOSFETS to sink the current from the LED's, and you're almost done

The 1st power MOSFET you'd connect to D0,
The 2nd power MOSFET you'd connect to D1, etc...
and when you figured you had enough progressive elements for the moving arrow, if you haven't gone through all 10 Dn outputs, just connect the 1st unused output to the RESET input (after disconnecting it from ground first, of course!)

That's it!

That's what I figured... Wow, that means I actually understand the circuit layout correctly! Basically I could eliminate the 4075 completely then, and attach the MOSFETs directly to the 4017 outputs... I guess the biggest question then, is whether it would be better to do this with a PIC or not..

IF I were to do this, (and it's still a big IF at this point.. lol) it would need at least 3 patterns.. Left, Right, and a generic flashing one.. (the standard triple flash you designed would work well for this, flashing certain batches of LEDs on the bar).. So I would have to wire up 3 separate circuits with an on/off switch for each.. Question is, could all 3 circuits be wired to the same LED array? (Multiple inputs for each little set of LEDs) Or could this create problems with current flowing where it shouldn't? Would it fry something if the not-so-great-with-electronics user were to turn on 2 or more of these circuits at once?

This started out as a simple project to give him some emergency lighting... Suddenly he wants me to completely outfit his car with all the best stuff..

 

Hmm, well, for changing from a sweeping right arrow to a sweeping left arrow - if you were just using three MOSFETs, you could just swap the inputs to the two end MOSFETS. If you were using 4 of them, you'd have to swap the first two inputs with the last two inputs (D0 and D3, D1 and D2)
If you were using five MOSFETS, you'd just switch D0 with D4, and D1 with D3; D2 would stay where it was.

Make sense?

As far as the LED array, that would take a bit of noodling around to figure out.

Did he actually want arrows, or just sweeps to the right and left? The sweeps wouldn't be hard to do if just vertical bars are acceptable. But if he wanted bidirectional arrows - things get more complicated.

Before we get into all that though, what LEDs did you order? Do you have a datasheet and part number for them? Who's the manufacturer?

 

...As far as the LED array, that would take a bit of noodling around to figure out.

Did he actually want arrows, or just sweeps to the right and left? The sweeps wouldn't be hard to do if just vertical bars are acceptable. But if he wanted bidirectional arrows - things get more complicated.

Before we get into all that though, what LEDs did you order? Do you have a datasheet and part number for them? Who's the manufacturer?

Well, for the array I was thinking something like a straight horizontal bar of LEDs, set up in either 6 or 8 "groups" of 3.. Most of the commercial ones light up each little pod sequentially, in addition to the ones already lit.. Something like this pic:

But even having each pod light up individually in a left-to-right / right-to-left sequence would work fine. (And is more eye-catching, in my opinion) So the current circuit idea would work fine as far as I'm concerned.

The LEDs I got from a distributer in Hong Kong, so I'm not sure of the manufacturer yet. But I can give you the specs for them:

Whites:
typical V is 3.4, max is 3.8
current is 100mA
it says they're 0.5w
light output is 280,000 mcd (aka bright as hell... hehehe)

Reds:
typical V is 1.9, max is 2.3
current is 20mA
doesn't give wattage
output is 70,000 mcd

Yellows:
typical V is 2.0, max is 2.4
current is 20mA
doesn't give wattage
output is 70,000 mcd

These are all the 10mm high-output ones, incidentally. I'll be building 2 of the flasher units, which will each be running 24 LEDs total. So the flashers shouldn't have to work too hard as the plans are now.. lol

 

Hey SgtWookie:

I had a brainstorm earlier today... (Don't know if that's a good thing, or a bad thing... )

I included a very basic pic to show the idea better, but I was curious... I know it wouldn't give the most elegant controls over the unit, but would it be possible to wire this hypothetical LED array/arrow stick to the multiple flash circuits I mentioned, but rather than having a separate on/off switch for each one, wire those circuits to another 4017 chip with a momentary push-button wired to the clock input? Turn it into a "Pattern cycle" button, per say? Or is this not really a feasible idea?

 

I haven't forgotten about you; I'm merely busy with something that came up suddenly. Well, not suddenly actually - just something that's taking most of my attention at the moment.

I'm still in the "noodling it over" phase. Yes, your idea might be viable, but I'm working out ideas in the background to use comparatively inexpensive components, rather than use a slew of MOSFETS (which is what your idea would require)

Let me continue to crunch on it for a bit

 

I haven't forgotten about you; I'm merely busy with something that came up suddenly. Well, not suddenly actually - just something that's taking most of my attention at the moment.

I'm still in the "noodling it over" phase. Yes, your idea might be viable, but I'm working out ideas in the background to use comparatively inexpensive components, rather than use a slew of MOSFETS (which is what your idea would require)

Let me continue to crunch on it for a bit

Works for me. Thanks again for all the help!

Most of my stuff should be here by the weekend... With the exception of the LEDs themselves... shipping time for them is 2-3 weeks unfortunately.. I'm debating on picking up just a couple cheap ones at radio shack this weekend so I can at least test my flashers once I build them. That way I can make sure they work before I switch gears and start building the light assemblies.

You think the ones I ordered should work ok? I've talked to a few other guys who are building their own lights like these, and they all went with the Superflux 5mms (the 4-legged critters you mentioned.. lol) because they put out a much wider angle compared to the 10mm.. (Although the 10mm are brighter by quite a bit)

I noticed that mouser sells 10mm optic lenses to spread the light out, but they run just shy of $2 each so it would add almost $80 to the cost of this project if I have to get them. I've got a few sheets of clear plexi I'll be using to seal the units up, so I was thinking of trying to maybe dremel a spreading pattern into them. (I've got a lot of extra, so I can afford to experiment a little)

 

Well, wide angle is good.

Yes, it does cut down on the peak brightness if the lenses are more wide angle. However, for visibility's sake, that's what you really want.

Those that are typically used for brake lights have somewhere between 120° and 150° lenses. They are also not a "true" red, but a red-orange; which appears somewhat brighter than if they were red. In most places, it is not legal to use a "true" red for brake lights.

Radio Shack has no "good deals" on LED's - they are all horrifically expensive. However, their "best deal" is the LED assortment. As with all LEDs (except for those which have built-in limiting resistors or are of the flashing type) you MUST use a current limiting resistor with them, or their life will be very short.

Find out what voltage each LED drops across itself, using a 5V or 6V power supply and a 1k resistor in series.

Once you've found out the Vled for a particular LED, you can choose a resistor to limit the current to 20mA max. You'll likely get better life from them if you limit current to 15mA.

Now that you've found Vled using the 1k resistor and the 5v power supply, you can calculate the resistor you'll need to limit the current through the LED.

Vsupply - Vled = Vremaining
where
Vsupply = any DC voltage level
Vled = the voltage drop you measured across the resistor.

Wait - we've been through this before, right?

 

Wait - we've been through this before, right?

LOL yup! I've done a few LED projects before, (albeit it's been a few years.... Ok, more like 10, but hey! lol) so I do actually know the basics about using resistors with 'em... I'm just hoping my trusty dremel can give me a good spread for these 10mm LEDs I ordered... The way they're being placed on the car gives a good spread of light as it is, but it would be nice to spread it even more.

According to the specs, the whites give off about a 40* angle, while the reds & yellows are about 20*... So while they're darn bright, they ARE a pretty focused beam.. I did some research on the types of lenses used by the commercial emergency light companies, and it gave me some ideas.. (Although most of them have now moved on to using the Luxeon LEDs which are a whole different ballgame.. lol)

 

Yeah, I have a few red-orange Luxeons I bought from a fellow on E-bay really cheaply. Dang, are those things bright!!

While it's certainly possible to re-shape them using a Dremel, it's going to be really tough to get them consistent, and centered. Plan on boogering up a number of them.

If they are cylindrical, you may be able to hold them using a collet-type chuck, and have them rotating as you re-shape the lenses, as in a drill press. If you don't have a collet chuck of appropriate size, but do have a 3-jaw chuck large enough, you could fake it using some copper or brass tubing that you've cut three slots along the length, 120° apart. The Ace Hardware stores I've been to around here generally have a stock of K & N brass tubing in one and three foot lengths; you're bound to find a suitable ID for your LEDs.

I've been pretty successful shaping/polishing Plexiglas and other clear plastics using a cotton wheel in my 8" bench grinder with emory and rouge sticks. It's mighty easy to overheat plastic items, though. Easy does it; allow plenty of cool-down time. Careful to not spin your cotton wheels too fast.

This is a project that just screams to be automated.

I hope you have a lot of patience - and cotton wheels!

 

For the enclosures I simply got some flat sheets of plexi... After looking at the lense designs of many of the commercial units, I noticed that a few have fresnel type patterns, but most simply have vertical grooves.. I figured that type would be a lot easier to replicate, so I'll probably just use the cutting wheel on my dremel to make a series of vertical grooves across the face of the plexi.

I can't say for certain though until the LEDs arrive and I can see in person how they perform. One of the commercial makers uses these 10mm LEDs, and doesn't put ANY sort of lens on them. They simply encase the whole thing in a silicone-type epoxy so they're completely waterproof. Their products seem to do fine without any lenses, so it may very well turn out that I don't even need to make any of my own. Only time will tell at this point..

 

Well, my mouser order showed up today, so I'm probably gonna start building the first flasher unit tomorrow after work. Wish me luck! I'll probably need it! LOL

 

You can also use the Pic 16F84. The requirement is that you must have:
o Pic Simulator
o Pic Programmer

Completing with this requirements, I will send you the program flow.

Best regards,
Real

 

Sgt. Wookie, this cicruit is exactly what I've been looking for but i've had some problems. I built it the other day and I have a short. I don't think its on the board, I think I'm supplying it wrong. I have 12v to position 1 of J1 and chassis ground to position 3. I have the negative of the led's to positions 5 and 6 of J1 and their positives to the same 12v as position 1. the LED's are 12V rated with integral resistors just for testing purposes. Am I doing this right? I think I fried the IC's but I want to make sure I have it right before I rebuild it. Thanks!

 

Sgt. Wookie, this cicruit is exactly what I've been looking for but i've had some problems.

I built it the other day and I have a short.

Why do you think you have a short? Did something emit smoke, or are you blowing fuses?

I don't think its on the board, I think I'm supplying it wrong. I have 12v to position 1 of J1 and chassis ground to position 3. I have the negative of the led's to positions 5 and 6 of J1 and their positives to the same 12v as position 1. the LED's are 12V rated with integral resistors just for testing purposes. Am I doing this right?

That all sounds correct, but I'm not sitting where you are.

Note that the Vdd/Vss connections to the ICs are not shown in the schematic; they are only shown on the board routing.

I think I fried the IC's but I want to make sure I have it right before I rebuild it. Thanks!

Since the active components are CMOS, it's not hard to "zap" them with static electricity. That can be a big problem as we're getting into the cooler fall season. Also, this circuit doesn't have any protection against overvoltage; it wouldn't be hard to burn things up quickly if it were hit with an electrical "spike".