Finally Affortable Snowfall Tubes (FAST)

chelmuth

chelmuth

New member
I've been working on an idea for inexpensive snowfall tubes.. What I've come up with so far consists of :
1-PIC 16F688
8-51Ohm 1/8Watt Resistors
1-10KOhm 1/8Watt Resistor
56-Pure White SuperFlux LEDs (Or Any LED, Depending on Vf the 8 resistors value might need to change)
My plan is not to create a PCB for these but take strips of white Formica and drill the holes for components. I know tedious but the idea is inexpensive and I've got time.

My plan is to power 1 tube per Ren48LSD Channel. Simply supply 5V to the tubes and they do a "fall".. I've written some Firmware for the PIC. I have 2 working versions. One is straight forward and loops through 28 times lighting 2 LED's each time through the loop with delays. The second is a variation with a TMR0 interrupt triggering the next run though the loop. Both Firmwares start with the fall going fast and then slowing as it "falls" I'm attaching the Schematic & Firmware for what I have currently working. Ideally I'd like to get it to a point where there are a few configurable options in the firmware such as setting a flag for maybe a "dimming tail" or other ideas. I'd like some input on the software and if possible some help with the code. I'm 1 week into learning assembly, so I know I've got a ways to go.

Here is a video of the LED's on my breadboard..
http://vimeo.com/22587872 (Uploaded at 11pm on 4-18-11.. Vimeo says it might take til midnight to convert. If it doesn't work try back)
 

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Your timing stinks... :) About the time you were waiting for the Video to upload and convert, I was finishing my Taxes and beginning to pull out all my Blinky Flashy stuff. I told myself that I had to get my Taxes done before working on my two new projects: RGB Sparkle Balls and Snow Fall tubes. My tubes were based on BobKeyes design. very similar to yours, but a simple 12 LED solution driven directly off the PIC.

I like the formica idea. For my My prototype I cut a strip of a piece pegboard and pushed the LEDs from the back.

Did you write your code from Scratch? I'm very impressed. Not sure I coudl handle the Matrix stuff.

If you haven't seen it, here's the post where Bob's starts:

http://doityourselfchristmas.com/forums/showthread.php?5870-Falling-snow-lights&p=107970#post107970

No matter what happens, I think most of the DIY designs could use this type of LED. Where did you get yours and what was the cost? Do you think it makes sense to do a Bulk Grup Buy? I struggle at pulling the trigger on LED purchases. I'm never sure on what I'm buying. I have been using a bunch of LEDs that were sold as replacement for LED strings. I bought every replacment pack the 3 Walmarts near me had for like .15 per pack of 5. They are not as bright as any LED I have seen in a tube, and have strange viewing angles, so I would like to use something different.
 
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Very nice. I have been investigating this same type of design, but never finished. I really like the idea and have looked online at some of the pre-made units but did not like the way they were triggered.

I would gladly be up for a group buy on this one. What length are you thinking of obtaining? And to be able to trigger it from Vixen is the best part.

Please keep me informed.
 
Now that I had a chance to look at the Schematic, my brain hurts. It looked like a matrix of some kind, but when I look at the mixed orientation of the LEDs, I don't see it. Can you explain the concept? Sorry, I'm a bit dense.
 
The LED's are CharliePlexed not regular Matrix. Basically you use 8 pins connected to each other as follows with 2 leds one forward biased and one reversed.. so you get 2 LED's per connection then when you reverse the high and low of any pair the other LED lights..so wires go from
1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8
2-3, 2-4, 2-5, 2-6, 2-7, 2-8
3-4, 3-5, 3-6, 3-7, 3-8
4-5, 4-6, 4-7, 4-8
5-6, 5-7, 5-8
6-7, 6-8
7-8...

This gives you 28 paths and when you put 2 LEDs on each path you get 56 total LED's..

The LED's I plan to use are the Pure White SuperFlux LED's for the superstrips that tjeitzer (sp) just did a group buy for.. Since we ordered 10k'ish the price ended up being 4$ for 60.. so for a final cost I'm looking at $4 LEDs, $.10 Resistors, $.14 PIC Socket, $1.50 PIC16F688, Optional RJ45Jack for Power Connection $.80.. Plus what ever the Formica costs if not free. and i'm thinking the 4' Florescent projector tubes which are ~$4.. So I'm thinking easily less the $14 total possibly less that $10 if you only make 2ft tubes..

Yes I did write the code from scratch.. That was a learning process (read "much banging head on wall going why the $#%@ doesn't it do what i'm telling it to) considering I'd never touched Assembly before 2 weeks ago.

My ideal length was either 2 or 4ft depending on how the LED spacing looks once I get the actual LED's i'm going to be using in place..
 
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All I know is that I'd like to get ahold of that I&%$#%$^ guy "Charlie" (Charles Allen) and wire his arms and legs up in opposing polarities. It's called Charlieplexing, and it uses a minimal number of output pins to control a large number of LEDs. Theory says you can control N * (N-1) LEDs with N pins. So for 8 pins you control 8 * 7 = 56 LEDs. You only need to keep all potential paths below the forward voltage that will light the LEDs. WIERD guy!!

See this Instructable for a pretty good explanation: http://www.instructables.com/id/Charlieplexing-LEDs--The-theory/



:)
 
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Thanks for the great explanation guys. I have heard of Charlie-Plexing, but I didn't understand it like that. My head still hurts! So in your schematic, how are they numbered?

I bought a few extra in TJs GB, but not that many.
 
kychristmas said:
So in your schematic, how are they numbered?
Click to expand...

Looking at the resistors they are in order.. 1-8 .. I used the same pins as the channel outputs for the renard software as I was originally going to mod some renard code but decided against it and rolled my own.. Maybe this schematic is easier to read?
 

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n8huntsman said:
Check out pages 8 and 9 of this for a good schematic and explanation of charlie-plexing. This really helped be get my head around it.
http://downloads.eshepherdsoflight.com/Howidid-MidiTree.pdf
Click to expand...

Actually, that is just an example of multiplexing, rather than Charlieplexing. With Charlieplexing, the state of each output effects the resultant selection, where in DonJ's megatree, each of 12 outputs controls a branch, while two outputs are used to select one-of-four colors for all branches.

Charlieplexing will light (or not light) one of two LEDs (or strings) for EACH PAIR of outputs. For example, (for two outputs) If A is high and B is low, then D1 lights; if A is low and B is high, then D2 (which is wired back-to-back with D1) lights. If A and B are both high or both low, then neither D1 nor D2 light. Again, the rule is N*(N-1) lights for N outputs. In this example, 2*(2-1)=2. The advantage comes when you build up the number of outputs feeding the matrix.

However, as you increase, you lose discrete control, unless you can tri-state (open-circuit) the outputs. Lacking that capability, for 8 bits of data, you can control 8*(8-1)=56 lights. Since there are 256 possible states (ON or OFF) of 8 bits, there are only two states with all lights off (00000000 and 11111111). All other bit patterns will result in 7, 12, 15, or 16 lights on. Actually 7 occurs 16 times, 12 occurs 56 times, 15 occurs 112 times, and 16 occurs 70 times. Each light is on in 64 of the 256 states.

(Isn't matrix math fun????) :roll: :roll: :roll: :roll:

As usual, I've gone on way too long, but that's me... (see my signature):D
 
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WireWrap said:
Charlieplexing will light (or not light) one of two LEDs (or strings) for EACH PAIR of outputs. For example, (for two outputs) If A is high and B is low, then D1 lights; if A is low and B is high, then D2 (which is wired back-to-back with D1) lights. If A and B are both high or both low, then neither D1 nor D2 light. Again, the rule is N*(N-1) lights for N outputs. In this example, 2*(2-1)=2. The advantage comes when you build up the number of outputs feeding the matrix.

However, as you increase, you lose discrete control, unless you can tri-state (open-circuit) the outputs. Lacking that capability, for 8 bits of data, you can control 8*(8-1)=56 lights. Since there are 256 possible states (ON or OFF) of 8 bits, there are only two states with all lights off (00000000 and 11111111). All other bit patterns will result in 7, 12, 15, or 16 lights on. Actually 7 occurs 16 times, 12 occurs 56 times, 15 occurs 112 times, and 16 occurs 70 times. Each light is on in 64 of the 256 states.
Click to expand...

Also, by adding bipolar transistors across the resistors, you can increase the I/O pin drive capability so that you can turn on multiple LEDs within a "row" of LEDs without burning out the I/O pin. An EDN article about "chipiplexing" a while back described that trick.

don
 
ErnieHorning said:
Of coarse as you know, using an appropriate optocoupler will allow you to drive nearly anything you want.
Click to expand...

I was thinking that optocouplers are used more for voltage isolation, but that's an interesting idea to use them for current protection purposes also. thanks.

don
 
Ok, I got my LED's in from the group buy and away I go.. Here are some pics of my first one.. Being that I'm lazy and cheap I didn't feel like going to the store and getting any formica to start this project. I had an old screen out of an old rear projection tv in my garage. The diffuser on the front of the fresnel lens has nice groves in it perfectly positioned to run a razor blade down it to score it and snap to the width I wanted. The screen I'm using happens to be around 24" tall If I want different size tubes I just find larger screens. People are always throwing these TV's away now what I nice way to recycle part of them. On a side note the Fresnel lens is very fun to play with but very dangerous. WARNING : It'll make a spot and get it 2000+ degrees.. You can melt glass and or steal or give yourself a nice sunburn.. So here are some pictures of what I've completed so far.. Not pretty but functional and the screen was free.

FAST1.jpg
FAST2.jpg
FAST3.jpg
 
Looks great so far. Hope to see the finished product by monday, and of course we will need video of it actually working so we can all want to do it.
 
Hi, trying to follow along with the schem.
All the LEDs in both drawngs are labled D?
Although the color "wiring"diagram helps, still not sure what sequence to wire the LEDs.

Oh, btw, I am planning on using 3/4" green plastic Banding tape we use at work. We throw thousands of scrap pieces away daily...
If anybody wants to try ths flexible pcb, pm me
 
Hi all, been semi-away for a bit.

I just came back from Home Depot after my weekly drool-fest in the store.

Flourescent tube covers.. about 2 bucks each and up to 4 feet long. They are clear and have caps on each end with an opening to allow the prongs to poke through.

Use those and a small pcb board for the hardware and run a ribbon-cable (or even a pair of cat5 cables) off the board and the leds soldered to the ribbon. a small elastic band keeping the ribbon cable taunt at the bottom, in the same fashion as the di-pole antenna tensioner.

Could not find a HD sku number online, but here is a UK store with the same items..

colouredtube.jpg


Protectedcovers.jpg
 
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