So! I was wondering:

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(Leo Bettinelli) #1

So!

I was wondering: What happens if you simply ramify a led strip? Simply solder new strips to the main strip, and so on?

I did it first with two, not expecting it to work, and it did work. now I did it with 5, curious; it does work. (see video)

two questions then:

-Can anybody clarify the electronics of this behaviour?
-How much can I continue ramifying?

:smiley:

light for all!
http://youtu.be/Gz90sDgqJWk

(Jon Bruno) #2

I can’t see your video with my phone but I know that if you cascade strand to strand you will eventually run into power issues.

(Leo Bettinelli) #3

ok. what kind of issues?

(Jon Bruno) #4

Well… for one, the longer the run the lower the voltage will be by the time it’s delivered to the leds. one way to combat that is to tap power in every couple of lengths… As to where depends on the power supply and requirements of the LEDS you’re driving. I’m sure there are limitations to the distance that the data line can be as well and that’s one other reason people use multiple MCU pins to run addressable LED strands. I guess those are the two major reasons… I may not have described the issues properly or as clearly as I could have but with any length of wire the voltage/current/or signal will be reduced when compared from one end to another. this may be evident by observing lower brightness or lost data

(Jon Bruno) #5

I just saw the video from my computer.
I guess the situation I explained doesn’t really apply with the configuration you have shown.
But I’d bet addressing that array may have a few caveats

(Herb Smith) #6

You get voltage drop (IR Drop) along the strip a which can result in incorrect color display among other weird and wonderful symptoms. Check prior posts to see what is reccommend for power feed; I personally add a new power feed about every 60 LEDS. I should add I hate voltage drop as messes with your signal to noise ratio which in-turn can create some of those "weird symptoms.

(Leo Bettinelli) #7

thanks guys.

I understand voltage drop and I still havent built anything big enough to experience it. but it is very good to have it in mind.

as for, How much can I continue ramifying? I would love to understand the electronics there…

(JP Roy) #8

Hi , actually the output from a device can usually drive many inputs in parallel, 10 or more.
The devices input current is usually so low ( in the microamps and devices can maintain the correct output low and high voltages while driving a few milliamps.

(Ashley M. Kirchner [Norym]) #9

Other than power issues, nothing’s wrong with what you’re doing. Eventually you will need to inject power along the strand. However you won’t be able to address individual pixels on the “side” strands as they are all the same as the main one.

(JP Roy) #10

I agree with Ashley,
you could easily split a single branch into 10 smaller branches and then each of these 10 smaller branches could be split into 10 tiny branches that could be split further down the line into minuscule branches etc… etc…
The problem here would not be with data signal integrity but with potentially excessive voltage drops along the power wiring. But that could be handled with a well designed power distribution wiring.
Of course, the animations would be limited as each parallel branches would always display exactly the same thing.

(Landon Meernik) #11

So I’m assuming these are WS2811/12, I suspect the principal is similar with SPI ones, but the encoding is different. In theory you can branch them as far as you want (assuming the voltage drop doesn’t cause artifacts, and if it does, you can patch in more down the line using fat wires assuming your PSU can handle it), the protocol doesn’t care.

The reason for this is because the way those work, each “frame” is a reset signal (long period of the data line being low) followed by a bunch of bytes encoded using a variable pulse time (similar to an RC servo, but differently shaped, faster, and digital, not discrete). Each light then sets its color based on the first 3 bytes in the stream, and retransmits the rest (with a reset in place of the bytes it just used), so the next light sees the second set of 3 bytes, changes its color, and retransmits the rest, so as the signal goes along the chain, each light chews off the bit of data it needs and sends the rest along.

The reason you can split them like this is because each light exchanges its data in the incoming stream for a longer reset period, so the signal is valid at any point in the chain, so you can easily just send one signal to 2 chains, and they’ll display the same thing, and because the output signal encoding is the same as the input (just missing 3 bytes), you can hook 2 strands up to the output of one.

If I ever meet whoever came up with this scheme, I’ll buy them a beer, or five, cause it’s awesome.

(Leo Bettinelli) #12

thank you very much guys for joining the conversation and sharing your knowledge!

(Luminous Elements) #13

Opinions differ on how often to inject power: https://plus.google.com/+BeLuminousElements/posts/jWBxGkCCz3m

(JP Roy) #14

Hi @Luminous_Elements ,
I had never asked myself that question until that little survey you did.
It think it is normal to have different opinions on this question of ‘How often to inject power?’
Not all strips are the same and some have surprisingly weak power distribution traces that will drop more volts as more current is drawn. They would obviously require more frequent power injections. The wire gage used to feed power and it’s length also has an influence.
In fact, the real question is… How much voltage drop do you accept anywhere along your strips ?
I only use 5Vdc devices and strips so no real data or opinion on the 12V stuff.
If you look at 5V devices like the ws2811/ws2812 or even the APA102, their spec sheets show electrical and timing based on VDD between 4.5Vdc and 5.5Vdc
So I would suggest to always design the power distribution such that you NEVER get a 0.5V drop anywhere along the assembly.
To be honest, I have always managed to not drop more than 0.1Vdvc in all my 5V electronic designs.

(Luminous Elements) #15

I’m glad to have prompted that thought :slight_smile:

I never meant to imply that there is One Right Way, of course. Different projects have different requirements. Some will be brightness-limited, or only light a few pixels at a time, and others will be lit with full-brightness colours at varying saturation levels. My current project is pretty bright, so I’m injecting power for every 120 pixels.

Perceptually, as long as the colour looks good, the system is doing its job. From an engineering standpoint, I think 0.5V drop is a good absolute maximum, since that’s right up against the minimum Vdd of most 5V pixels. It also limits power dissipation as heat, which could be a real problem in enclosed projects.

(JP Roy) #16

@Luminous_Elements
Did not want to imply that you implied either… :wink:
I also supposed all answers in the survey were based on real life, working projects and therefore are all perfectly good answers !
Just felt that some clarifications would be useful to explain the need for injecting power more or less often.
On the other side of things, having to ‘inject’ power more often may add complexity, cost and may even affect aesthetics.

These are all factors to be considered when designing power distribution for larger LED projects.

(Justin Eastman) #17

Cool that I saw this today. I thought this guy would be a great project to make with LEDs. This reminded me if it!

(Ashley M. Kirchner [Norym]) #18

1024 LEDs … well, 1024 “tips” at the end. Way more when you add the branches.

(Justin Eastman) #19

Is there really a limitation on ws2811? @Ashley_M_Kirchner_No ​ I thought it cleaned the signal up everyone… Just good to note. 1024 us a lot. Never chained more than 250 together but good to know limits

(Ashley M. Kirchner [Norym]) #20

Not so much on the ws28xx ones …