A Rotating LED Light Bar
by Sandy Sims


  I know, I know, it looks really complicated, and probably will end up looking very different from this picture, but one has to start somewhere right?  These LED's are 3 watters so need to be mounted on a heat sink made from aluminum angle or flat bar. The cool thing about LED's is they can be over powered momentarily to get almost twice the brightness, which is perfect for a stage light show! I propose the bar (lighted area) will be 48" long. It was going to be longer, but then packing it around would become an issue. I could always make a second if I need more.

 The power consumption is something else at these low voltages. I plan to parallel the LED's in pairs which will allow a pulsed supply of 5 VDC to work with it. A desktop PC supply that can deliver about 30A @ 5 volts will be fine. ( and cheap! )  ...also because the color lines would be 32 otherwise!  Too many for a wash light.

  I have already drawn up 3 different schematics, but have found this one to be the best. Note only 24 lines go to drive the LED's. The last design had 48, when I realized that's a lot of wires to fit through the hollow shaft the whole thing spins on. Also programming for 24 is less complex.

  I have found some MOSFET drivers that are way over-rated, just to be safe, but have a small case size so lots can be fit into a small box. At $.55 each ($.42 if you buy 25) they fit the bill financially as well.
On Ebay, china is selling 3 watt LED's for less than a dollar each now, a considerable price drop over the last few months, and if you decided to build this in the future, they will probably be even cheaper.

The 74LS374's ( octal latches ) are being used to free up some pins on the PIC microcontroller. The bus will be updated at the PWM period / 256 in sequence, which isn't an issue as these chips are fast. The "oe" on those is Output Enable, and can be used to easily blank the LED's from software, without effecting the individual PWM counts. This may be useful for halving the brightness or overload conditions etc. I may add a decoupled drive circuit so if the PIC hangs, the LEDs go out.

The EEPROM is a recent addition. I decided it'd be cool to use a MIDI sequencer to program lighting sequences under a 2 note identifier to recall them. This way, it doesn't have to be manually controlled from every song I create a MIDI sequence for. I like automation, especially on stage, and this is automating an automation, so I really like it!! (Update: Used this on the StripLights, works great!)

The motor drives will depend on DC motor or stepper motor. The second motor is to control a bezel that comes around 180 that has a magnifier in it. (Top image lower lightbar) So the light can be a wash, or a focused bar, say, 15 wide. Because the light bar rotates right around, the audience can be flashed as well.

  There is a pot that is tagged "SEL". This pot will enable manual selection of different preset sequences. Perhaps Club modes, Acoustic modes, Disco modes etc. The feedback will be the LED's when selecting. This will effect how the Audio automation will function. i.e. in Club mode, Low frequency beats will trigger timing on the sequence. In acoustic mode, signal level will trigger change in lighting colors. In disco mode it may be a combination beat/frequencies/levels.
  The other pot is a feedback voltage from the shaft, so the PIC knows where the thing is at any given moment. I've designed this type of system before, and it needs *some* intelligence, but overall, it's pretty reliable.

Apart from the mechanics of the whole thing, this project shouldn't be too hard to do. (Famous last words haha!) As the project gets under way, I'll update this page!

October 23rd 2012


  As with all wonderful ideas, seeming so simple and eloquent to begin with, something always throws a monkey wrench into the works. The monkey wrench in this case is lens focal point.
  As can be seen in the set of diagrams to the left, focal points change with the amount a lens runs around the radius of a circle. I have just discovered this after beaming an LED through a clear cylinder 1/4 1/3 & 1/2 full of water ( to act as the lens.)

It seems the point at which to focus a nice tight beam needs to be back on one end of the clear cylinder, or completely outside of it. By the time the lens is thick enough to focus a nice line on the wall, there's no room left for the LED mount assembly to rotate.


What a disappointment that was!  F&%#-*(#⌐!!

After that, I decided a clear rod mounted inside the tube might focus well, but discovered the material ( plastic ) refraction would mean the LED would need to pretty much touch the rod.
  A reflector behind the LED ( bottom drawing ) would work, but couldn't be moved, thus taking away all coolness of the thing. Ugg! What a mess!

Suddenly, after a few days of thought, I came up with a way to have my cake and eat it too. A reflector made from a section of 4" pipe...polished on the inside. Now I must work out materials and mechanics for this, but so far it's looking good.


November 10th 2012 update:

Lately I have been working on the Strip-Lights project while waiting for materials for this to show up at the scrap yard (lol) but a thought had occurred to me. This bar is like the Strip-Lights on steroids! 144 LED watts vs. 14 LED watts. So if there are screw ups with that, better to get them ironed out with the small power / cheap LEDs than this project ($50 worth of LEDs, and $24 worth of MOSFET drivers etc..)
  The two projects are similar in programming as well, but this one is simpler. Now I hope my poor daisy-chained MIDI bus can handle it all. :))


Update March 2013:
As you can see, the project has gone from paper ( well PC paper ) to reality at last! I wasn't in any big rush and I had a number of other "more important" projects to do before this, but now I'm free to dabble. The LEDs are spaced 15/16" and there's 48 of them as promised, so that makes the LED's  42" + ends (3" * 2) = about 48".
  I made it this size because things tend to come in 4' strips. Screwing in 96 little #4 screws was a bit of a job, but the heat sink compound is down and the wiring is done! Unfortunately I had to strip the cover off of the nice stranded CAT-5 cable I found at the scrap yard or it wouldn't have fit into the bar near the end. 42 wires, Pretty packed!


The gear box was made from a couple pieces of aluminum plate, and I used some nylon gears I had...against my better judgment. I always swear when they fail, but here I am using them myself. The shafts should have absolutely no play, but the big gear wasn't centered properly ( came that way! ) so I had to allow the center gear to wobble a bit. It works fine even off of a 1.5 volt C-cell and has quite a bit of torque.

  I went with a DC motor which can be controlled by PWM type signals on a MOSFET and DPDT relay (instead of a complicated 4 MOSFET H-Bridge) This will work as long as a few mS are allowed for the relay throw/release period before applying power through the MOSFET. (No sparks!)

  Next I made the "box" that will house the PC Boards. That's the round drum-thing. I was going to go square, but looks are important right? I've split it to open, and will put some hinges on one side and a snap catch on the other. I've learned over time to make it as easy as possible to access the circuitry. This is as easy as it gets because it doesn't matter which way it sits inside.

The board mounts  stiffly rotate to make it easy to get at either board. The wires will feed from the bar into a steel coupler shaft made from plumbing pipe, then into the aluminum drive shaft and out of a hole cut in the side.

  The steel coupler I'm especially proud of!
I managed to machine it in the lathe, square one end, weld on the box mount plate, and press and tack on the reflector gear mount plate without wrecking the coupler.  The reflector gear is now mounted on the main shaft so I don't have to worry about mounting the motor the the already over crowded control box housing. This way, there must be a take-off from the shaft that supports the reflector, but the motor can be mounted off of the reflector itself.

The only problem I have with this is the motor wiring limits how much the reflector can turn, so I'll have to add some sort of mechanical stop to prevent wires getting wrapped around and around.

  The reflector is going to be a big buffing job, and perhaps a bit of welding. I've never welded aluminum before so it'll either work or be a total disaster lol! We'll see.

  Another change was deciding to mount the PC power supply inside the drive unit. Sure it'll make the whole thing bigger, but I like the idea of just plugging in a power cord with no big messy box next to it cluttering up the floor. I will be taking the power supply out of it's original box though, so it's just a board and fan.
Well that's about it for now! I'll post again soon. Cheers!


  Update: April 4th 2013  
  Finally I worked up the courage to cut out and polish the reflector! It's just less than 1/2 of an aluminum pipe I carefully jig sawed then welded end plates on to. I've never welded aluminum, but this worked out ok.  It's not very heavy, about 1 lb, but I'll still need to counter weight it.

  The little gear assembly came together nicely. I don't know what it was originally, but I managed to find a motor with a proper size gear in my junk box. The whole plate pivots, spring loaded, just in case the reflector drive gear is slightly out of alignment.

  All of the bushings on the shafts are made from nylon bread board plastic. It's durable stuff, and works will if there's a bit of grease on it.

The support frame, about 5' long, is made from electrical conduit and scraps of steel plate, so it needed a really good coat of primer before painting. (below)


  I had mentioned the power supply will be built in, so that dictated the minimum size of the box. I had to use a PC power supply because of the large amperage, but if it ever blows, the form factor for these is pretty much the same so a replacement would be easy.

  The tall image to the extreme right shows the whole unit all together. I did some tests with a 1.5 volt "C" cell on both the drive & reflector motors and it turns nicely and slowly. With 3 volts it turns pretty quick. I mounted a 10-turn pot with a gear off of the drive motor's 2nd gear, which will be the position feedback to the PIC chip. It allows for over 2 turns and I didn't use a stop pin (although I still may add one to the reflector) because it must be used on the floor, or the ceiling. Thus, the drive will be shifted be 180.

  The reflector will only have 4 positions, so I drilled 4 holes in its main gear for an IR LED/Sensor. I decided to mount the reflector drive motor on the reflector which means it can only turn once, but it is nice and solid.


 Now the mechanical side of the project is complete, I'll be moving on to the electronics.  Almost all of that must fit into the round case on the shaft, so it'll be a challenge to get it all wired on. Oh! The 50 (was 42) wires just barely fit through the shaft to the light bar! Cheers *

These are light level tests sans processor. The picture on the left is so bright the colours wash out totally! The picture above is fairly dim so the colours can be seen. Aimed into the reflector it acts as predicted, but not a perfect solid line, more like two because of the bar being in the way, and a bit of distortion. When the bar is moving it won't be so noticeable I'm sure.

 There's no problems with heat on the aluminum bar, which is a relief! It get's pretty warm but not hot. The size of the aluminum channel is working to dissipate the heat. Had it been thinner, it probably wouldn't have.

Dec13th 2013 Update:
  Even though the program isn't finished, I had the opportunity to use this as a floor light for a performance with a few local musicians. On e guy is like "This is way too  bright" so I had to change it to red. Wow! I thought, I'm willing to sacrifice getting blinded by a spotlight  while on stage, as long as it's shining on ME! LOL
There's a problem with the audio section (inside the "mail box") being so close to the power supply with so much amperage flying around. I guess I'll be either moving it to an external, or perhaps into a small box on the other end, or making it a box that plugs in (which kinda sux) , not sure yet. I wrote an intelligent formula that ramps the lights nicely on the dimmer side, but still only uses 128 dimmer positions from MIDI. A sorta Log(10) pattern if you graphed it. I've been so busy with other things lately, the lightbar has just been a "dumb" light over summer and fall, but I'm starting back in to fix it up over Christmas. ;)


Disclaimer: This is not an instructional page to build or manufacture the above project, nor are there any guarantees of accuracy herein.
This page is an "of interest" discussion, and the project is intended for my own personal use.
If you have any questions, or wish to pursue this project, you may contact me (Sandra) at fresh(at)freshnelly.com