LED panels, controllers, or how to make an LED display, part one

It wasn’t for nothing that someone once said that appetite comes with eating. I can confirm that 100%. I’ve already posted two reviews of LED panels—although, more accurately, one review and one follow-up. Today I’ll tell you about higher-resolution LED panels, controllers, and my dealings with the sellers.
So brew yourself some coffee or tea, get comfortable, and settle in for a long read.
Warning: this review is very long and may be a problem for users on metered connections.


I should probably clarify that, as last time, I ordered the panels and everything else for a friend, not for myself. He’d used the previous display and decided he wanted something bigger, which is why we placed this order.
He chose the equipment, designed the enclosures, and handled the installation. My part was ordering everything, testing it, and trying to figure out what was what and how to control the whole setup.
There were plenty of adventures, and some are still ongoing, but I’ve already drawn most of my conclusions, so I can tell you about our saga with the new scrolling display.
I should also mention that there may be some mistakes, since this is only the second scrolling display I’ve tried. And I only spent a few days experimenting with it. This review is an attempt to write down everything I learned along the way so I don’t forget it.

First, it’s worth noting that this is no longer just a “scrolling display,” but a fully configurable screen capable of playing video, so the price is different too.

First, let’s talk about why LED panels.
1. High brightness and contrast
2. You can choose any size and aspect ratio.
3. They work reliably even at low temperatures
4. Repairable
5. Convenient software
6. Standalone operation (no PC)

But there are drawbacks, too:
1. Low resolution
2. High price.


Featured in this review:
1. LED 64x64 panels pixels—12 units, delivered for $300 ($20.50 per panel plus shipping)
2. HD-D10 controller (about $30, excluding shipping)
3. HD-D30 controller (about $40, excluding shipping)
4. Two 5 V, 40 A power supplies, bought locally for about $13 each.

That comes to $400, not including materials for the enclosures, glass, temperature sensor, and other odds and ends.

I ordered the controllers first because I was trying to negotiate a discount from the panel seller, since the order total was fairly substantial.
In the end, I couldn’t get a discount, and he shipped the panels about a week later. They arrived about a week before the controllers, though; shipping took around 10 days in total.
I received two fairly large packages, wrapped so thoroughly that you could easily play football with them or use them as pillows. The second photo shows just how much packaging material there was.


The panels were ordered in two separate packages because of customs restrictions, but they were also packed differently inside. One package simply contained 6 panels separated by soft material. In the other, they were sealed in plastic in pairs and additionally padded to prevent damage.
That difference made me a little uneasy right away, and my hunch turned out to be right.


All in all, I ended up with a pretty impressive stack of panels and a pile of different cables.


Let’s start with what’s included. Each package contained 6 ribbon cables for connecting the data lines, three power cables, and a small pile of plastic bits.
That makes 12 ribbon cables and 6 power cables in total.


1, 2. The power cables are standard for panels like these: two crimped ends on one side for connecting to the power supply, and two connectors for the panels on the other.
3. The ribbon cables are about 10–12 cm long. One was faulty, but luckily I had some spares left over from the previous panels, so I didn’t have to go to the market.
4. A pile of plastic fragments fell out of the first package (the one where the panels were packed separately). Most of them were pins used to align the panels when mounting them on the frame. They stuck out and broke off during shipping. We didn’t need them, so we just ignored them.


But besides the pins, the cable latches on some of the ribbon cables were broken too. That’s manageable, though less than ideal.
On the left is an intact ribbon cable, in the middle one with no latch at all, and on the right one with a broken latch.


And here’s a panel.
But first, it’s worth explaining how panels differ from one another.

Shape
As obvious as it may sound, the most common shapes are rectangles and squares. Often, a rectangular panel is sized so that its long side is exactly twice the short side, i.e. Essentially, these are two square panels.


I talked about rectangular panels in my previous review; this time I bought square ones.


Dimensions
This is all very straightforward. The key dimension, oddly enough, is the panel thickness, since the length and width are determined by the resolution and pixel size.
Since the pixel size is 3 mm and the resolution is 64×64, we get 64×3 = 192 mm. The panel is square, so its dimensions are 192×192 mm.


Brightness
Sellers sometimes just make this figure up, even though it matters quite a lot. Outdoor panels are usually brighter than indoor ones. Naturally, they also consume more power.

Protection
Panels are available in outdoor and indoor versions.
Outdoor panels are coated with a silicone-like protective compound that keeps moisture away from the LED contacts and circuit board.


The LEDs are also often covered with small sunshades to protect them from sunlight. You can see these on the left side of the photo; I’ll point them out in other photos too.


But since I planned to use the panel indoors, and inside an enclosure at that, I decided to buy unprotected panels, especially since they’re usually cheaper.


LED type
SMD or DIP.
Large panels, especially outdoor ones, sometimes use conventional through-hole LEDs.
These LEDs do have one drawback that’s rarely mentioned. They have a lens on the front that can focus sunlight onto the LED die, burning it out. So, in my opinion, unencapsulated LEDs are more reliable.
You can also see the large sunshades here.


Our panel uses SMD LEDs.


Before I move on to a more detailed description of the panels, let me cover a few other features.

Pixel shape
Square or rectangular.
The panel with square pixels is the one featured in this review; I’ll show a rectangular-pixel panel separately. These are usually inexpensive, low-resolution models, better suited simply as advertising signs.


Color
Single-color, two-color, or three-color (RGB, or full-color).
There are also panels with four LEDs per pixel. Most often, the extra LED is red, since red accounts for the largest share of power consumption. I’ll show this later.
I deliberately chose a photo with conventional LEDs rather than SMD ones. I think it makes things clearer, since SMD LEDs often have a single package shared by all the colors.
Single-color panels are used where you need something bright, cheap, and easy to see. Full-color panels are well suited not only to displaying photos, but also to use as video walls.


Pixel size
This is enough to make your head spin: the range of pixel sizes isn’t just large, it’s enormous.
For square pixels, the usual sizes are P37.5, P31.25, P25, P20, P16, P12.5, P10, P8, P7.625, P6.26, P6, P5.95, P5, P4.81, P4, P3.91, P3, P2.5, P2, P1.9, P1.6, and even P1.25.
The number after the letter P indicates the pixel size in mm. For example, P4 means a 4×4 mm pixel. There’s also a double designation, such as P10 P16, meaning a rectangular 10×16 mm pixel.
Some of these sizes are less common than others. The smallest I’ve seen for sale (though I wasn’t specifically looking) is P2, with 2×2 mm pixels.
Larger screens use larger pixels, and smaller screens use smaller ones.
By large screens, I mean ones like these:


Or even ones like these, in the form of a ceiling.
In general, screen size is limited only by your budget. What’s more, LED screens don’t have to be flat; they can have any shape—spherical, concave, or even wavy.


The most common module configurations.


Number of pixels
The vertical count is usually 8, 16, 24, 32, or 64.
There are more options horizontally: 16, 32, 64, 96, 128, 160, or 192. There may be models with even more.

Some of this information is shown in the table and in the spoiler below.




Scan mode
Since the information is refreshed dynamically, there are several scan modes: 1/32, 1/16, 1/8, and 1/4. I’ve only come across 1/16 and 1/32.
I may be mistaken about this, but as far as I understand, panels with 64 pixels vertically are arranged as two 32-pixel sections, so they use 1/32 scanning. However, they don’t work with all controllers—though I’m getting ahead of myself.
There’s a table above that includes photos, resolution, and scan mode. The important thing here is that your controller must support the same scan mode as the panel. Basic models usually support only 1/4, 1/8, and 1/16, while more advanced ones also support 1/32.

The module itself.
Most often, the module is a complete unit. Essentially, it’s a circuit board with LEDs on one side and control electronics on the other.
In some cases, the plastic frame can be quite sturdy, and outdoor models may also have additional seals.


In some cases, though, they use an aluminum frame, especially for larger modules—the plastic simply wouldn’t be strong enough.


In our case, we probably had the simplest version: a lightweight plastic frame with metal nuts used to attach the modules to the main frame.


A standard four-pin connector is used for the power supply, the same type found in many kinds of displays.


Since the panels are often daisy-chained, there are two connectors for the data bus. Markings next to the connectors indicate the signal path and, accordingly, the order in which to connect the panels.


As before, the board has control ICs, LED drivers, and shift registers. If I’m not mistaken, they’re the same ones, just in greater numbers.


As before, the panel housing isn’t rectangular in cross-section; it’s more like a trapezoid. This makes it possible to butt the panels together with no gap, or even with a slight curve—for example, to wrap them around cylindrical surfaces, although the radius would have to be fairly large.


Connect two panels and it looks something like this. Then you simply connect as many panels as needed in a row to get the desired width.
Adding rows vertically is even easier: the next row simply connects to the next output on the controller.
But keep in mind that you can only add a certain number of panels (especially lengthwise). Beyond that, you’ll either have to stop or reduce the refresh rate.


As I’ve already mentioned, the order contained 12 P4 panels with a resolution of 64x64 pixels. They weren’t intended for a single screen, but for two. But if you put them all together, you can make a screen about 600x800 mm (1 meter or 39 inches diagonally) with a resolution of 256x192 pixels.
To build a FullHD display from these panels, you’d need 30x17=510 panels, making a screen 5.76x3.26 meters in size. For comparison, the largest wall in a typical apartment living room is 6x2.65 m.


Naturally, that makes for a large display, but panels with a finer pixel pitch are available and can produce a very good-quality image.


The panels arrived first, and to test them, my friend brought over the Onbon bx-5ql controller we used last time.
At first I planned to test them one at a time, but my friend suggested testing four at once to speed things up.
1. We put together a setup with a power supply, controller, and four panels, then started testing.

The first thing we noticed was that the controller lit up only part of the panel: just the second and fourth quarters horizontally.
Of course, this controller isn’t designed for panels like these, so I wasn’t particularly concerned.

2, 3. But when I decided to take a photo “for the record,” I happened to notice something odd. We were testing the third (last) group of four panels, two from one shipment and two from another.
My friend noticed the difference first, and then I did too. The image colors were different. So we switched to a solid-color mode and saw that two colors—green and blue—were swapped. We opened my own review and checked the order in which the controller displays colors in its test, which let us figure out which panels were working incorrectly.
4. Just to be sure, we swapped the outer panels around, and confirmed the problem: the panels from one shipment displayed the colors incorrectly. and the red and white are displayed correctly, which is quite understandable.

I immediately wrote to the seller about all this, and got the following reply: which controller had I used?
I replied that it was an Onbon bx-5ql.
The seller said he used a different type of controller.

Well, okay, a different one it is. We decided to wait for the proper controllers and then figure out what to do. Maybe the problem really wasn't with the panels.


The panel on the left displays colors correctly; the one on the right has green and blue swapped. At the very beginning I mentioned that some of the panels were sealed in plastic. Those were the good panels.
The panels also differ in appearance, with more mounting points.


There are also some differences in the PCB layout and components.


By the way, last time we bought extra panels for the first line, we also received panels of a different version, but that didn't cause any problems then.


A few more photos of the components, just in case they come in handy.


The controllers arrived about a week later, but first I'll explain a little about what they're for and what types are available.

As you can probably tell from the description, unlike monitors, LED panels can't display anything on their own, since they're essentially just LED matrices without a controller.
Controllers range from relatively simple models with little memory to fairly advanced ones, although even those are just enhanced versions of the basic models.
Some controllers can also output audio.


Control programs can be uploaded not only via a COM port or USB drive, but also via Ethernet, Wi-Fi, and even GSM.


Like quite a lot of modern systems, they also support operation through the "cloud".


Besides standalone controllers that can operate on their own, there are also models that connect to a computer. In this case, a special card is installed in the computer and fed the signal from the monitor; the card then outputs a control signal to the panel controller.


The control setup in this case looks like this.


There are also some downright "monstrous" options, but ordinary users are unlikely to need them.


You may be wondering why some boards have two Ethernet ports. When building large displays, the control boards can be daisy-chained.
But while the boards in the previous examples operated asynchronously, since each controlled just one display, this setup uses synchronous operation. Each controller displays its own section of the image in sync with the others.


The controllers were ordered from another seller and shipped via Nova Poshta; I have no complaints about the packaging. Each controller came in its own bag, labeled with the controller model.


The complete set I bought consists of:
1. HD-D10 controller - link, price including shipping: $33.96.
2. HD-D30 controller, link, price including shipping: $45.63.
3. The second controller comes with a hub for connecting the panels.
4. There were also two CDs with software. The disc color matches the color of the sticker on the controllers—a nice touch.



Since the controllers belong to the same series, they share a common description. There's also a D20 version, but for some reason it wasn't included in the description. Maybe that's for the best, so it doesn't cause confusion.
As you can see, the difference isn't that great.


Compared with the previous Onbon bx-5ql controller, the board size and the ability to connect to a local network are immediately noticeable. But the differences are actually much greater, and if you've tried something like the D10-D30, let alone the more advanced C-series models, and especially the A-series, you won't want to go back. but more on that later.


First, let's take a look at the smaller D10 board.



At the end of the board are the power terminal block, a connector for connecting to a local network, and a USB port for a flash drive.


On the other side of the board are four connectors for LED panels. With four connectors, you can connect four rows, which can operate in sync.


As with the other models, the board has footprints for connectors for additional devices, a button to enable Test mode, and a battery for the built-in clock. There are also two LEDs indicating the operating mode.


1. There is a footprint for a WiFi module connector at the top of the board.
2. The footprint for the GSM module is at the bottom.
3. Near the panel connectors is an LED indicating panel operation.
4. A resettable fuse is installed at the power input for protection.


The whole thing is controlled by a processor with Chinese characters in its marking. As far as I know, it's based on the Cortex ARM A9 core. There's a heatsink glued on top, but I didn't remove it, partly because I'd have to glue it back on, and partly because there's not much point.
The heatsink gets quite hot during operation.


1. The board also has an Altera Cyclone IV. I suspect it's what outputs the signal to the panels.
2. The heatsink on the processor is glued on oddly, offset rather than centered. And it's the same on both boards.
3. Micron flash memory. Presumably 2 GB.
4. 256 MB of RAM.
5. A 2M x 16 Bit x 4 Banks Synchronous DRAM chip. I didn't quite understand its purpose here; I assume it's dedicated RAM for the “Altera.”
6. Real-time clock. It's strange that it's so far from the battery.


1. Ethernet controller
2. Bidirectional buffers for connecting the panel data bus.
3. LT8619, HDMI/MHL Dual-mode Receiver
4, 5, 6. Power converters for various sections.


The second board looks almost the same, apart from a few minor differences.



In fact, there are virtually no differences on the underside.


The connectors are exactly the same, and even their positions are identical. There is also a footprint on the left for soldering a WiFi antenna connector.


Since the boards are so similar, I'll just show comparison photos and describe the differences from here on.
First of all, the markings, as well as slight differences in the placement of some components. At first glance, everything seemed identical, even the board dimensions.


The differences on the underside are even less noticeable.


Perhaps the most important difference is the presence of an mPCI slot; the previous board only had a footprint for one.


I tried one of my WiFi modules, but it wouldn't work. It also clearly isn't the right length, so there's no way to secure it.
An SSD definitely won't work in this connector, although it is the right size. But even if you buy a WiFi module that fits, it probably won't work either; I suspect drivers are available only for certain models.
If you need WiFi, you should buy the version that comes with it.


As with the previous model, an Altera Cyclone 4 controls the panel output.


The panel output is arranged somewhat differently here: a single shared connector is used, with the signal routed through the same 74HC245 buffers.


To connect the panels, you need to use a hub, or splitter—whichever you prefer. This factored into my choice when buying, since the hub is often not included and has to be purchased separately. The hub is sold together with the controller.


The hub board also has 74HC245 buffer amplifiers, so it’s not just an adapter from the 50-pin connector to 4×16. By the way, the screenshot above showing the board specifications includes a table listing the connector pin assignments.


The definite downside of this design is its height. You can use a ribbon cable instead of plugging it in directly, but it’s best to buy one together with the board, since the male connector that crimps onto the cable isn’t always available offline. Another option is to crimp a 50-pin connector onto the cable and solder the hub board to the cable.


As far as I know, the vast majority of panels, like the controllers, run on 5 V. So I bought a 5 V, 40 A power supply for the project. Yes, the currents here are high; there’s no getting around that.
I bought a second power supply after the first one passed its test.
In our case, the power supply will be located separately. With this setup, you need to use short, thick wires. Alternatively, you can install a 12/24-to-5 V converter inside the panel and power the whole assembly from a 12 or 24 V power supply.
There were two reasons for putting the power supply outside: less heat inside the panel and a thinner enclosure.


Since the store gave me a one-year warranty on the power supply, I didn’t open it up; I inspected it through the case vents. And honestly, I wasn’t too impressed by what I saw. The output capacitors have a total capacitance of 6600 µF (3 × 2200), the inductor is rather small, and it makes a noticeable ringing noise at loads above 40–50%, which is quite annoying. The overall build quality is pretty poor, too; the only things that make up for it are the low price and the warranty.
Of the suitable options on AliExpress, I can recommend a couple: one, two.


That wraps up the section on the hardware. In the next part, I’ll talk about the software and continue dealing with the “quirks” of the panels and controllers listed above.