Sending cards and receiving cards explained

What does a sending card do?

A sending card takes a video input — HDMI or DVI from a PC, player or processor — and turns it into the data stream that LED cabinets read, distributed over one or more Ethernet outputs. It is the point where an ordinary video signal becomes an LED signal.

The sending card may be a card inside a PC, a standalone sending box, or built into an all-in-one video controller or multimedia player. Whatever the form, it holds the global settings for the wall: overall brightness, colour temperature, gamma and the map of which part of the picture goes to which output port.

Its capacity is set by its ports. Each gigabit output carries roughly 650,000 pixels at 60 Hz, so a larger wall needs more ports or more sending devices. Our NovaStar controller guide explains how to size this for a given wall.

What does a receiving card do?

A receiving card sits inside each cabinet, takes its share of the data from the network cable and drives the LED modules in that cabinet, line by line, many times a second. It is the local brain of the cabinet.

It handles the low-level work: the scanning pattern of the modules, the driver ICs, the refresh rate, grey-scale processing and, on many systems, the calibration coefficients that make every module match its neighbours. The receiving card connects to the modules through a hub board, and passes the remaining data on to the next cabinet through a second network port.

Because the receiving card is configured for its specific module type, a receiving card from one screen will not simply work in another. That configuration file is the most important thing to keep safe after commissioning.

How does the picture get mapped across the wall?

During commissioning the engineer builds a map telling the system which cabinet sits where and in what order the cable reaches them, so each receiving card picks up exactly its rectangle of the picture. If the map is wrong, the picture appears scrambled, mirrored or in the wrong cabinet.

Cabinets are daisy-chained: cable from the sending card to the first cabinet, then cabinet to cabinet in a snake or column pattern, with each chain staying within one port’s capacity. A 4 × 2 m wall of 500 × 500 mm cabinets has 32 cabinets, which might run on two or three chains depending on pitch.

The map lives in the sending device and the configuration software. We save a copy of every client’s configuration on handover, so a replacement controller can be loaded and the wall restored without rebuilding the map from scratch.

What goes wrong, and what does it look like?

A failed receiving card usually shows as one cabinet dark, frozen or garbled, while a failed cable or port shows as every cabinet after a certain point going dark. Recognising the pattern tells you where to look before anyone opens a cabinet.

A single cabinet showing wrong colours or flickering often points to a receiving card or its connection to the hub board. A whole chain dark from one cabinet onwards points to a cable or connector between that cabinet and the one before it — common where cables are pinched, unplugged during cleaning or exposed to moisture. A wall that is entirely dark or frozen points upstream: the sending device, its input or its power.

Many walls are cabled with a backup loop, in which a second cable returns from the last cabinet to the sending device. If one cable breaks, data reaches the cabinets from the other end and the picture survives. It is cheap insurance on any wall that matters.

Why must spare receiving cards be configured?

A new receiving card arrives blank or with someone else’s settings, so it must be loaded with your screen’s configuration before it will drive your modules correctly. A spare card in a drawer is only useful if someone has that file and knows how to send it.

In practice we either preload spares with the client’s configuration at handover or load them on site from a laptop at the time of replacement, which takes minutes. Where calibration data is stored on the receiving card rather than on the modules, that data must also be restored, or the cabinet will look slightly different from its neighbours.

This is one reason we hold spares in Kathmandu and keep configuration records for every screen we install. Under our two-year manufacturer warranty, a failed card is a configured replacement rather than an import and a guessing exercise.

Do brand and model choices matter?

Yes — sending and receiving cards must come from the same control system family, and the receiving card must support the module’s chip set and scan type. Mixing systems is not possible; mixing models within one family usually is, within limits.

Most LED walls installed in Nepal use NovaStar control, which has the advantage of widely available spares, software and trained technicians. Higher-end receiving cards add features such as finer grey-scale at low brightness, better calibration storage and support for high refresh rates — features that matter on fine-pitch indoor walls and anything filmed.

When comparing quotes, ask which control system and which receiving card model are included. Two walls with the same LEDs can perform differently because of the cards behind them.

Common questions

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