Looking for Specialty Light Circuit

Jure George

Joined Dec 28, 2008
51
Hello

I am looking to create a beacon from small yellow LED like a simple light chaser circuit for 4 LED in a round mounted configuration, not your concern for the mount.
It is powered from either 6v upto 12v D.C battery. I would like to use a 555 if possible, no knowledge with PIC crts.

Can this be done? Can you show me a circuit with the ability to vary the speed the LEDs turn on and off, that way when they are mounted in a round plastic dom, like seen on top of a truck or forklift, I could adjust the speed of the light rotation or chasing etc.

I tried to search but dont know enough about what how to phrase the search question, Lots of accumulated info. here.

George

Joined Apr 30, 2011
1,570
It's fairly easy to create a sequencing circuit for 12V using a 555, CD4017 and some transistors. If you're trying to re-create the look of a typical rotating safety beacon using common 5mm LEDs, I'd suggest sequencing 6-8 groups of LEDs arranged in a hexagonal or octagonal pattern since their viewing angle is usually 45° or less.

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Jure George

Joined Dec 28, 2008
51

Thanks for the info. I have seen one done with 4 3mm yellow LED because the scale of truck used, 1/16, 1/14, that amount of LEDs looks great But in the video the maker used Only a 555 with resistors and caps to make this work. The truck battery was, not sure, 6v, 7.2v, 12v Max.
So can you show me a working circuit that will be able to be adjusted through a variable resistor for the flash rate. Physical circuit size is important. Smaller the better.

I thought I heard somewhere that a 555 alone could handle 4 - 3mm LEDs at 20mA.

Thanks Again.

George

Joined Apr 30, 2011
1,570
The 555 alone can only blink two circuits on and off alternately but it might work for a small model. You could have for example 4 LEDs, 1 each facing to the front and back and 1 to each side so the front and back would be on together while the sides were off, etc.

Check out Bill Marsden's blog on LED circuits on this site.

You don't say how much space you have to fit the LEDs into. If necessary, you can use tiny surface mount LEDs.

Wendy

Joined Mar 24, 2008
21,929
Could you give us a footprint, outside diameter, shape, and where you want the LEDs. We will also need a general idea if the mounting scheme, if it is holes in the board. I prefer inches, but I'll use that yucky french system.

The schematics already exist in abundance, though they are not exactly what you want. You will likely need SMT parts if it needs to be really small.

Since the requests for help were the same, I closed this thread.

To Mr. Bill Marsden

We can continue the conversation over here instead.

Jure George

Joined Dec 28, 2008
51
Hello Again

It is the exact specs as the email question under To Mr. Marsden. As for sizes, for now Im experimenting with 3mm Yellow LEDs in as tight group of four as I can get them. Im not worried about the plastic covering cap for now.

All I can saw for my specs, LED 4, 3mm Yellow LED, 20-25mA, 6v min. 7.2v average, 12v Max. D.C battery. Would like to mount this ontop of a 1/14, 1/16 remote control truck to act as a warning Beacon.

I would like to have a variable resistor to adjust the rate of which the LED #1 -- #4 turns On/Off. So it looks like it is going in a none stop circle. I would like to repeat, I know a 4017 should be used with this to creat a chaser circuit But the cobination of the Two I.Cs is a little large to find a good place to hide it. Also it must be noise resistant because of the servo motors and main drive motor gearbox near it. I would like to know if I could encase the entire circuit in either epoxy or similar to make it water proof OR would that affect the operation and life of the circuit, water could be present. The ONLY way I want it to stop is by being turned off, manually or electronically.

I thought that I saw an article before Reg. the 555 being able to do this by itself so I ask the experts here. If the experimentors version works good, I might try using SMD LEDs to make it smaller later. If I have to use the 4017 as well, can someone show me a circuit using Only the 4 LEDs and I guess I need a transistor also to drive the LEDs. Give me an optional circuit that will handle 5 LEDs to do the same thing.

Please can you help me with this? I need a circuit with parts list. Thank you.

George

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Wendy

Joined Mar 24, 2008
21,929
I can and will, but need the ideal board footprint you need.

I'll try to work around that.

Think where this finished project would go, where the LEDs would be. Then give me a drawing or verbal description.

During the work week I get a bit distracted (and stupid from lack of sleep). Just PM me if I haven't responded in a while.

Jure George

Joined Dec 28, 2008
51
Hello again

Not sure I understand what your question is, I plan on having the beacon mounted eventually on the roof of my r.c truck.

For now I am using a experimentors peg board, not sure of the proper name of it, long white plastic board with lots of rows of pin holes that allow components to be inserted temporarily and have a electrical connection between them, for design testing purposes.

George

Wendy

Joined Mar 24, 2008
21,929
How much board space do I have, and what is it's shape? It is the first question you should ask when starting a project like this. The electronics is simple, but if the finished board doesn't fit...

Jure George

Joined Dec 28, 2008
51
O.K I understand now.

For now can we go without specific size and go on the belief thats its gonna be the smallest board possible for I.C use not SMD BUT I will probably use a 1 1/2 " x 1 1/2" square circuit board and wire it myself. In the future I might replace the 3mm LEDs with SMD yellow LEDs so the beacon would be even smaller diameter.

Not important for this experimentors version for now.

Thanks Again for All Your Help.

George

Bernard

Joined Aug 7, 2008
5,354
Might a 558 in a loopback config. make a 4 step rotating beacon? Disadvantage would be 4 RCs, but still would be just one 16 pin IC capable of driving 4 LEDs, with limited speed control.

Wendy

Joined Mar 24, 2008
21,929
I thought about that. Problem is, lots of resistors and capacitors, plus the real chance of erratic operation.

I'm leaning towards a 4022 and a 555 myself.

Funny thing, I have a few SMT type 556's, now if I could get 555's. These suckers are tiny.

I will be back, the schematic I'm leaning towards is a variation of Figure 9.2

The difference between 6.8ma and 20ma isn't as great as the OP thinks it is. I've never done this, but I wonder if the current limiter components (including the resistor) can be eliminated all together. The 4022 may smoke, but CMOS has some odd characteristics in that reguard.

Audioguru

Joined Dec 20, 2007
11,251
with a 12V supply, a Cmos logic IC has a typical output current into three 2V red LEDs in series (without a current-limiting resistor) of 18mA and a minimum output current of 9mA.

Its output transistor will not get too hot.

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Wendy

Joined Mar 24, 2008
21,929

I would normally never try this, but it looks like an interesting experiment, the kind I love.

What can I get by with today.

Audioguru

Joined Dec 20, 2007
11,251
Yes, but the output transistor will be dissipating 216mW which might melt it.

Wendy

Joined Mar 24, 2008
21,929
Point taken.

The OP did say he could use less voltage for the power supply. Have variable, will test to destruction.

Ahhh, reminds me of when I was a student. Maybe I can brand a fingertip. It is has been decades for me.

Jure George

Joined Dec 28, 2008
51
Hello All,

I was just wondering if there was any more progress to my request of a light circuit?

Thanks Again to All who have joined in here.

George

Wendy

Joined Mar 24, 2008
21,929
What you see is what we got. My current thought is several approaches. The schematic on post #12 is pretty close. If you must have 20ma on the LEDs then you could use MOSFETs like 2N7000 for the job, or some low logic level equivalent.

For the variable resistor / cap use a 1µF cap (they are really tiny, check the tantalum cap from Radio Shack out) and up the variable to 100KΩ. You can find small multi-turn variations pretty much everywhere out there.

With a 6VDC or 7.2VDC power supply you could probably get by without any current limiting resistors off the 4022 or 4017 (the 4022 uses 2 less pins, smaller footprint). The drawback is much less current on the LEDs. This may not be as big a deal as you think though, since LED brightness is pretty nonlinear to current.

My time on the weekdays is pretty slim. At the moment I'm running extremely short on sleep. This isn't to say I won't be here, but I am not at my sharpest.

We will need a layout of the LEDs. What is the diameter of the circle?

Jure George

Joined Dec 28, 2008
51
Hello Again,

Thanks for the information above. Could someone tell me what the purpose of the Green LED #D13 in Post #12 is? Is it to show that the circuit is on? Also since I will be Only using 4 Leds, from the LED pattern on the Right side of Post 12 again do I use D1, D6, D8, D10 to act as my rotating beacon? And forget the other LEDs?

All my LEDs are Yellow not Red. Can you explain the function of the U3 LM317T please.

Again Thank You all for your help.

George

Wendy

Joined Mar 24, 2008
21,929
U3 is a current regulator. After a bit of experience I'm beginning to think it isn't that needed, but it is highly effective, even on LEDs that use up to 1A.

The reason that circuit exists is to teach the concept of light chasers, which is what you are going for in it's simplest form. Just eliminate the unwanted LEDs, as you said.

The green LED is to show the oscillator operation, and can be eliminated. I through them in there as a demo, you can see how the 555 beat works with the other LEDs.

LED color varies a bit in voltage, but they are all fundamentally similar.

Like I said, I will redraw this circuit. I will likely modify this one, since it would be quicker that starting from scratch.