Video Wall advice (240 * 32)

[sermad]

Hi all,

I'm starting out on a diffused video wall to cover a large space approx 4 meters (wide) * 2.8 metres (tall).

I'm ok with programming ardunio / processing so going back to electronics is a little bit of a challenge for me. I really appreciate the many smart minds on this forum!

So. Going by OctoWS2811 LED Library page - I've divided up the wall into 8 segments of 60 * 16 - 960 pixels per segment

I not sure which orientation I should use - either lay the strips horizontally or vertically. But right now I'm leaning towards horizontally as then I can keep the strips together - as they come as one 4m length.

If I do it this way then i'll space the strips approx apart 9cm to get the 2.8 mete coverage I need. I'm hoping the scrim fabric I use to diffuse the colours should cover any dark spots. Hope that makes sense. I'm not running video across the display but using it for ambient animations so perfect density of the strips is not necessary.

Kit list

8 * Teensy 3 - 1 per segement

8 * 5V @ 60A PSU - 1 per segment

Adafruit NeoPixel Digital RGB LED Weatherproof Strip 60 LED - 1m - I'm buying from Adafruit as they can deliver very fast and quality control should be good.

1 - USB

Questions

If I run the strips as 4m lengths - Do I need to power the strips either end? Will that be ok?

Is running 1 teensy per segment (960 pixels) under using them? Can they run more? If so - roughly how much?

Is running 1 PSU per segment (960 pixels) under using them? Can they run more? If so - roughly how much?

I believe the PSU's are 60 amp and are 3 * 20 amp - So would they power 5-6 strips each? Do you wire them in series? What guage do I use? Bit worried about *this* to be honest!

How can I control the brightness of the LEDs other than keeping the colours in less bright rangers?

Can anyone recommend an 8 port USB hub that would power all 8 of the teensys?

Will the frame sync work with 8 segments?

Thanks all.

Really appreciate the community here.

Edit - I've added a schematic.

 

[PaulStoffregen]

If I run the strips as 4m lengths - Do I need to power the strips either end? Will that be ok?

You'll probably need to apply power to both ends.

From the diagram, it looks like they're going to be cut into 2 meter segments. 2 meters is probably about the limit to powering from only 1 side. When I tested with 1 meter strips, I measured about 0.25 to 0.30 volts drop from one side of the strip to the other while they were running at fully white (max power).

If your strips are similar, powering 2 meters from both ends means the ones in the middle should see a drop of only about 0.25 to 0.3 volts. If you power from only 1 side, the LEDs at the far end will see at least double this drop, which is right near the limit of what can work.

I would personally just run the wires so each 2 meter segment is powered from both ends. That's extra work, but it's usually easier to put wires in during the initial build than it is to add them later.

Is running 1 teensy per segment (960 pixels) under using them? Can they run more? If so - roughly how much?

The 1000 LEDs recommendation is a bit conservative. I'm considering updating the page to recommend 1000 to 1500.

In a system this large, those $19 Teensy3s are probably the least expensive part, so you'll save very little money by pushing this limit.

Your diagram shows all 8 on the left side. I would recommend place 4 on the left and 4 on the right, so each Teensy3 drives 8 strips of 120.

Is running 1 PSU per segment (960 pixels) under using them? Can they run more? If so - roughly how much?

If you set the LED to fully white, it uses about 50 mA. 960 * 0.05 = 48 amps.

I personally like to avoid running a power supply right at 100% rated power. Usually above 50% on any power supply means you should pay attention to adequate cooling, but of course it varies depending on the PSU's design.

If you're using a cheap no-name Asian power supply, as most people do for these LED projects, check its voltage output under load. Also, check the current rating. I've seen several that claim 350 watts, but then the rated current is only 50 amps.

I believe the PSU's are 60 amp and are 3 * 20 amp - So would they power 5-6 strips each? Do you wire them in series? What guage do I use? Bit worried about *this* to be honest!

Each power supply should power a group of LEDs. For an equal number of power supplies and Teensy3s, it's simplest to have each power supply power up the same group of LEDs as a single Teensy3.

Do not connect power supply outputs to each other, as shown in the wiring diagram. Only very special power supplies (typically used in high reliability server systems) are designed to have their outputs driven by another power supply.

There are a couple other things to consider for a display this large.....

7680 LEDs, if driven to 100% white, will draw approximately 1900 watts of power. Cheap 5V power supplies are usually about 70% efficient. That would result in about 2750 watts of power drawn from the AC mains. Ordinary 120 volts lines in the USA usually are limited to 15 or 20 amps. You'll almost certainly have to run this thing from 240 volts.

The other possible issue is inrush current when you turn on the power. The really cheap power supplies have little or no inrush current limiting. When you turn on the AC, even if they're not driving any load, there's a pretty big surge of current to initially change their input capacitors. Even on the display I built, which is only one quarter this size, it make a noticeable flicker on lights in the same room when initially plugged in. As you scale up to larger sizes, this might become a problem. Then again, it might be a non-issue?

How can I control the brightness of the LEDs other than keeping the colours in less bright rangers?

That's the only way.

Will the frame sync work with 8 segments?

It should. I'd recommend a low capacitance coax cable if the Teensys are located on both sides of the display.

If you don't need precise frame syncing, you could edit the code to transmit to all of them as masters, so none waits for a frame sync signal.

 

[sermad]

Thank you again for this amazing response.

You'll probably need to apply power to both ends.

From the diagram, it looks like they're going to be cut into 2 meter segments. 2 meters is probably about the limit to powering from only 1 side. When I tested with 1 meter strips, I measured about 0.25 to 0.30 volts drop from one side of the strip to the other while they were running at fully white (max power).

If your strips are similar, powering 2 meters from both ends means the ones in the middle should see a drop of only about 0.25 to 0.3 volts. If you power from only 1 side, the LEDs at the far end will see at least double this drop, which is right near the limit of what can work.

The segments will be 4 meters wide. I've tested them on a 5v 10amp psu at 4 meters and could visibly see the brightness of the LED at the 4m end get brighter when I wired both ends. So I'll indeed wire up both ends.

I would personally just run the wires so each 2 meter segment is powered from both ends. That's extra work, but it's usually easier to put wires in during the initial build than it is to add them later.

The 1000 LEDs recommendation is a bit conservative. I'm considering updating the page to recommend 1000 to 1500.

In a system this large, those $19 Teensy3s are probably the least expensive part, so you'll save very little money by pushing this limit.

Your diagram shows all 8 on the left side. I would recommend place 4 on the left and 4 on the right, so each Teensy3 drives 8 strips of 120.

I'll try and use each Teensy3 to drive 4 strips of 240.

If you set the LED to fully white, it uses about 50 mA. 960 * 0.05 = 48 amps.

I personally like to avoid running a power supply right at 100% rated power. Usually above 50% on any power supply means you should pay attention to adequate cooling, but of course it varies depending on the PSU's design.

If you're using a cheap no-name Asian power supply, as most people do for these LED projects, check its voltage output under load. Also, check the current rating. I've seen several that claim 350 watts, but then the rated current is only 50 amps.

Each power supply should power a group of LEDs. For an equal number of power supplies and Teensy3s, it's simplest to have each power supply power up the same group of LEDs as a single Teensy3.

Do not connect power supply outputs to each other, as shown in the wiring diagram. Only very special power supplies (typically used in high reliability server systems) are designed to have their outputs driven by another power supply.

Very much noted. I'll update the schematic to address this.

There are a couple other things to consider for a display this large.....

7680 LEDs, if driven to 100% white, will draw approximately 1900 watts of power. Cheap 5V power supplies are usually about 70% efficient. That would result in about 2750 watts of power drawn from the AC mains. Ordinary 120 volts lines in the USA usually are limited to 15 or 20 amps. You'll almost certainly have to run this thing from 240 volts.

I haven't spoken to our electrical installer so I'm going to ask some very naive questions here. Say we have two 120 volt sockets. What sort of equipment would we need to drive the 8 60amp PSU's.

The other possible issue is inrush current when you turn on the power. The really cheap power supplies have little or no inrush current limiting. When you turn on the AC, even if they're not driving any load, there's a pretty big surge of current to initially change their input capacitors. Even on the display I built, which is only one quarter this size, it make a noticeable flicker on lights in the same room when initially plugged in. As you scale up to larger sizes, this might become a problem. Then again, it might be a non-issue?



That's the only way.



It should. I'd recommend a low capacitance coax cable if the Teensys are located on both sides of the display.

Can you possibly recommend a US supplier for this type of cable.

If you don't need precise frame syncing, you could edit the code to transmit to all of them as masters, so none waits for a frame sync signal.

Between the PSU and LED strips, is 12 gauge is recommended?

From the teensy3 to the LED strip data in - does this need to be any particular wire? I think I read cat5 was working well?

Can the ground cable from all the LED strips need to be any particular wire?

 

[PaulStoffregen]

I'll try and use each Teensy3 to drive 4 strips of 240.

That requires setting the strip length to 240, which is the same as driving 1920 LEDs from a single Teensy.

Might be possible, but not recommended.

I haven't spoken to our electrical installer so I'm going to ask some very naive questions here. Say we have two 120 volt sockets. What sort of equipment would we need to drive the 8 60amp PSU's.

I'm reluctant to give highly specific advice here. Whatever your on-site electrician says trumps anything in this message. He knows your building configuration. I don't.

But I can tell you building are typically wired with numerous circuit breakers, where groups of sockets connect to each breaker. Obviously, if you plug into 2 separate sockets on the same 15 amp breaker, even though you may be drawing only 11 amps from each socket, all 22 would need to flow through than 15 amp breaker.

Also, keep in mind these numbers are very rough guesses, not solid specs. 50 mA per LED is approximate. Especially the power supply efficiency is a guess. It might be better or even worse than 70%.

Can you possibly recommend a US supplier for this type of cable.

Not off the top of my head, no, sorry. You'll need to do some searching.

Between the PSU and LED strips, 12 gauge is recommend?

This is actually a pretty general question about wire sizes and voltage drops. You've got 5 volts and probably about half the amperage a strip draws. You can look up resistance per foot for wire sizes and use ohms law to estimate the voltage loss. I would aim for no more than 0.1 volt loss long the wire from the power supply to either end of the LED strip. Don't forget the current goes through both wires, so 0.1 volt drop is 0.05 on the +5V line and 0.05 on the ground return.

From the teensy3 to the LED strip data in - does this need to be any particular wire? I think I read cat5 was working well?

See the section about signal quality. The longer the wire, the more important this becomes. Keeping the wires relatively short helps.

Can the ground cable from all the LED strips need to be any particular wire?

Well, that depends. Certainly the ground wires from the strips to the power supplies carry the full current, so they need to be as good as the power wires.

 

[sermad]

My bad on the pixels calculation.

1 row = 4 meters - 60 pixels per meter = 60 * 4 = 240 pixels.

I'm running 4 rows per teensy 3 = 960 pixels.

Your code states the height must be a multiple of 8 but I was going to attempt changing it to accommodate the layout of pixels I require.

Again thanks for the help.

 

[PaulStoffregen]

OctoWS2811 always drives 8 strips.

You can connect only 4 of those 8, but the library is still designed for exactly 8. It it absolutely fixed at 8 strips. You can not change it to 4.

 

[sermad]

OctoWS2811 always drives 8 strips.

You can connect only 4 of those 8, but the library is still designed for exactly 8. It it absolutely fixed at 8 strips. You can not change it to 4.

I think my initial diagram suggested I was running 8 meters per row but I'm running 4 meters per row.

I am running 16 strips / meters per teensy3 (4 rows at 4 meters - 60 pixels per meter = 960 pixels).

Your tutorial shows 16 strips just stacked differently - Hence why I thought it would be possible to adjust.

Diagram to confirm.

 

[PaulStoffregen]

OctoWS2811 always output 8 simultaneous data streams. How you're planning to connect those isn't clear to me from your message and diagram. But ultimately it's up to you.

If you haven't already read the "LED Addressing & Different Strip Lengths" section on the OctoWS2811 page, I would highly recommend you pay careful attention to that part. The 1000 LEDs per Teensy3 recommendation is the number of LEDs OctoWS2811 is configured to use, not the number you actually connect.

 

[sermad]

Thanks again paul.

My power supplies haven't arrived so I tried a test to see if a 5V 10Amp psu would drive 8 metres (Edit 16 meters now working @ 25% brightness).

I'm using the adafruit neopixel and now to move onto trying to control the strips with the teensy3 and the OctoWS2811 or the FastSPI_LED2 library (I have this working on one pin).

 

[sermad]

OctoWS2811 always output 8 simultaneous data streams. How you're planning to connect those isn't clear to me from your message and diagram. But ultimately it's up to you.

If you haven't already read the "LED Addressing & Different Strip Lengths" section on the OctoWS2811 page, I would highly recommend you pay careful attention to that part. The 1000 LEDs per Teensy3 recommendation is the number of LEDs OctoWS2811 is configured to use, not the number you actually connect.

Hi Paul - I think I'm going to run 4 teensy3's with each one running 8 rows @ 240 pixels.

I'm starting to make good progress.

Would it be possible to elaborate on how you send the pixel data across the serial - the format you are doing this. If I can get to the point I understand this, then I can send any pixel data through the serial and I'll be well on my way.

 

[sermad]

Just running the numbers again and I'm bringing down the size of the wall as I'm still not 100% confident on the power we are dealing with.

We have 6 sockets in the space. Assuming they are 20 amp so far. Electrician to confirm.

The coverage I need is 4.00m by 1.68m

So I've calculated 240 pixels by 24 pixels - with a 7cm distance between the rows.

0.04a per pixel (I will never run them white) = 240 * 0.04 = 9.6 Amps per row

60 Amps per PSU / 9.6 Amps = 6.25 ~ 6 rows per PSU

24 Rows / 6 rows per PSU = 4 PSU's

The PSU's are rated 300W. 300 / 120 = 2.5 > 2.5 * 4 = 10 Amps...

New diagram.

 

[PaulStoffregen]

Don't forget the power supplies are not 100% efficient.

 

[PaulStoffregen]

Looks like you're running 288 watts per 300 watt power supply, with the software-imposed limit of 40 mA per LED. By those specs, you're technically 12 watts under the 300 watt limit. If you only hit 40 mA briefly and infrequently, it might work pretty well. If you make a mistake in the software, you could easily create a load far beyond the power supply ratings. Even if you're at only 288 watts, many power supplies should not be run at or near their max rating. Especially with cheap no-name Asian ones, the max rating might have been for a superior design they copied without authorization, before swapping out the expensive capacitors for cheaper ones.

You're also using 3 Teensy boards to drive 5760, which is double the recommendation of 1000 per board.

I would design this system using 6 Teensy boards and at least 6 power supplies. One lesson I've learned (and re-learned several times, sometimes painfully) is that the hardware components like power supplies in systems like this cost relatively little compared to the cost of redesign or even repairs that don't change the design. Aside from the simple monetary costs, unexpected problems lead to downtime. Servicing something like this isn't cheap if it's mounted securely to a wall and access is obstructed by people, furniture, and other stuff. Cutting corners for small savings in material cost is a risky gamble. You might get lucky and have zero problems, for a best case scenario of 50% savings on a part of the project which is probably only a relatively small part of the total cost (certainly the LEDs are the lion's share of the total material cost).

Another hidden consideration you might think about is your own credibility with any other people involved in this project. Even if you're funding the whole thing, presumably its installed at some location where a successful project will reflect well upon you, and troublesome issues will involve your name being mentioned when people look upon it not operating and when the unexpected costs and hassle of servicing it are incurred. If you spend 10% or even 30% more, the cost to your own credibility is minimal (especially if you had anticipated that cost from the beginning). But if your cost savings turn out to be unreliable, having to repair or worse, redesign and rebuild a big project after it's already installed will really cost you credibility with other people involved.

 

[sermad]

Thank you again Paul for the amazing reply.

I actually bought 10 PSU's and 10 Teensy3's to hopefully cover any major mishaps and I'm evaluating your 6 PSU / 6 Teensy arrangement.

Running 6 PSU's on a 20 Amp supply circuit is just about within tolerance correct(?).

 

[PaulStoffregen]

Running 6 PSU's on a 20 Amp supply circuit is just about within tolerance correct(?).

Regarding the safe capacity of your building's electrical system, I'm going to defer to your electrician.

I've already written plenty regarding estimates of power usage. A big unknown is the specific efficiency of those power supplies. That information can only come from the power supply manufacturer, or your own testing of the actual power supplies. I've already made some very rough guesses. I just don't have specific and accurate info for these parts you've purchased from other companies (only the Teensy3 part comes from PJRC).