Color changing/fading LEDs

[t3chguy]

Hey Guys,

color changing/fading LED circuit. Does anyone have an easy way of doing this? I looked at those LEDs that change colors on thier own but there is no way to predict or repeat a fixed color pattern. So right now the plan I have it to have 3 LEDs, Red, Green and Blue and put them in close proximity to each other being able to change 7 different colors by turning them on and off. Now for fading I was going to use a ramp to fade them in and a cap to fade them out but this doesn't allow me to use a FET necessary to get the 4.5A of current drive that is required. So now I have a 555 setup as an oscillator that drives a 555 setup as a PWM device. Futhermore I have another 555 setup as an oscillator driving into a 4017 counter IC that cycles through a count of 7. Each output from the 4017 turns on a FET that allows the PWM to pass signal to the gate of a high current FET that FINALLY turns the correct LEDs on and off in the correct order fading in and out while chaning colors. There must be an easier way to do this? Any ideas or suggestions? I have drawn a block diag below to try and clairify the current situation.

[555 osc.]---[555 PWM]----s FET d --------- g FET s--12V
g d
| |
output of counter RED LED
| |
[555 osc.2]-----4017 Counter GND


This would be for just red the same would occur for each with the PWM train always being present at the source of each FET and being allowed to pass when the counter/MUX turned on the fet allowing it to turn on the high current FET that will drive the LED. The plan is to have 100 of each color of LED which is why the 4.5A FET is being used.

Hopefully that gives you guys an idea what I am trying to do here. Anyone know an easier way of doing it?

Thanks,

T3CHGUY

 

[VEBill]

Your local 'Dollar Store'. They sell the exact item already built, with batteries, for $1.

 

[VEBill]

Except not 4.5A...

Radio Shack, or The Source by Circuit City, sells the same sort of thing (better quality) for about $10.

They are probably based on a specific Chip-On-Board IC. Perhaps you could add external FETs to the COB.

 

[geekEE]

Why don't you just use a microcontroller instead of the 555 and 4017? It'd be smaller and so much more flexible.

 

[t3chguy]

The Radio shack/walmart ones run on a 5V supply which isn't enough voltage to turn on the larger FET. This meant I had to run a smaller FET to turn on the larger FET and once it was hooked up it lasted about 45 seconds before the goofy little potted on PCB circuit decided that it had worked for long enough and packed it in. Either the draw from the FET was too much which seems strange as there was a 1Mohm resistor at the gate of the FET or something else went wrong. Anyhow I was hoping for something a little more reliable.

Unfortunately it has been a long time since I have done anything with a micro-controller. The last time I designed around one it was a Motorola 68HC11 and was programmed completely in assembler code. Presumably there is something small and simple that would accomplish this but I don't have anything to program it with and I don't know what is available that would suit this purpose. I don't really want to spend a bunch of money on a programming module and software and so on to program a micro that I will likely only make use of once or twice.

Any ideas?

Thanks for the posts.

 

[felixc]

McGyver2000 is our LED specialist. He's done lots of LED circuits. He shall have something to say about your subject. Hey Dan where are you?

 

[itsmoked]

He will be a firm believer in a Micro as am I. There are hordes of 8 pin ones that would handle this with vastly superior results. And if development is totally abhorrent, you should consider a PICstamp that you can program with your PC.

http://www.parallax.com/html_pages/products/basicstamps/basic_stamps.asp

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jimkirk]

A thought on another aspect of your project...since you apparently have a 12 volt supply, instead of driving 100 in parallel with 4.5 amps (and a bunch of power wasting resistors to drop the voltage) make some series groups. With 12 volts you can get 3, maybe 4 in series. Green and red even more. That way instead of throwing away 8 or 9 volts times 4.5 amps, you can limit that to maybe a volt or two at around one amp. Much cooler.

 

[MacGyverS2000]

Sorry guys, I've been quite busy searching for a new job (and with all of the frustration it entails, maybe a new career ;-) ). Also, this sounds more like a home-app/school project type thing rather than an actual work project, and I tend to shy away from those (regardless of the cool subject).

As Keith noted, I'm a fan of micros for jobs like this. With 4 parts (micro, 2 caps, and a v. reg.), you just replaced multiple 555-based PWM circuits that have no connection to each other (i.e., no common control). Considering many development environments are free (ala MicroChip) and programmers can be made at home for under $20, the claim of too great an expense falls on deaf ears.

All of that said, what kind of LEDs are you running?! 4.5A for 3 LEDs is way beefy... sounds like you're using 5W LumiLEDs (or similar).

Your diagram is incomplete, for sure, so I have to make some assumptions. First, move those FETs to the low side (between ground and the LED), and make sure you're using processor-level units (i.e., you can use 5V signals to turn them on)... if you're using typical FETs with higher turn on voltages, you could be burning them out by not turning them on all of the way.

Also, I see no resistors from your supply to the LEDs. If you're missing those, the voltage has to get burned up somewhere... typically the LEDs will try to pull as much as they can in that kind of setup, gladly blowing a low-powered FET.

I also hope you are using some massive heatsinking. A 5W LED will toast itself in about 10 seconds without a heatsink larger than your fist attached to it (forced air cooling is a good way to go here).


Dan - Owner

http://www.Hi-TecDesigns.com

 

[t3chguy]

Hi Dan,

Thanks for the reply. 4.5A is used to drive 100 LEDs of each color. The schematic was meant as more of a block diagram kind of thing to try and use a visual as an aid to my written text so that people didn't get confused and think what is this guy talking about.

This is a home-app kind of thing this is something that a friend of mine asked me to build for him. He wants to mount them on a set of motorcycles. It's part of the "flare" he wants to add to his bikes. He runs a "wheelie" school and wants to attract peoples attention off the track as well as when the bikes are on the track.

In response to the use of a micro I can certainly go that route but where to begin now becomes my problem. Do you have a recommendation, a fovorite? A quick search for a suitable micro came up with give or take about a bazillion and three different options. Atmel, Motorla, PIC....and so on. Do you/anyone know of a good low cost micro with development kit?

Good luck on the Job hunt and thanks for the help.

 

[itsmoked]

I take it you missed my PIC stamp link t3chguy? That would be the best route for a one off.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

Even if you were to run each LED in parallel, you're still talking 45mA each, and that's not your typical Radio Shack LED. If some will be in series, the current through each string increases even more, and heatsinking is going to be a requirement.

Look at MicroChip's website... you can download their development environment called MPLab for free, and they have some 8-pin units that are cheap and quite powerful (I use a 12F629 to control RGB LEDs as well as accepting input from the user). You may even get away with some of their 5-pin units in SOT-23 sized packages. Google for PIC programmers and you'll find a thousand of them as DIY projects for under $20. As projects get bigger, some of the other companies may make better chips for any one intended purpose, but when it comes to ultra-low pin count stuff, MicroChip has 'em all beat.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[analogkid2digitalman]

May not be of use, but I came across info on these PWM dimming drivers for high power LED driving at Linear if anyone is interested

http://www.linear.com/3476/index.jsp

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~