Led matrix display going to confusing condition

max7219 led matrix

Hi for all,
I sold one big led message display with 1000 x 5 mm led.
On the place where I put this display, I use power from line who also powered 20 neon lights. (I use PC SMPS)
When I turn on the display start normaly, but after 10 seconds all leds going to confusing condition.
The display have 4 digit big clock, he increase value for hours every 10 or 20 seconds.
After that I use RSO filter to put down this interference, but no help, problem still exist,
Somebody have a solution for this kind of problem,
regards

Based on your description, it seems like the LED display gets corrupted on its first update. I would guess that you are updating the LEDs with a serial scan chain. It sounds like this serial data is getting corrupted.
I have worked with these systems before. Usually they cannot handle large amounts of LEDs illuminated at the same time without ground bounce and other signal problems. When the display gets corrupted, does it stay in that state until the next update? Or are the LEDs constantly changing?
Do you have control of the firmware? Can you blank the LEDs before each update?

Serial scan chain drivers usually have a clock, cs and data lines. Is the output of the last chip wired back to the processor for comparison purposes? If so, you can do a software verify of the data to see what part of the chain is getting corrupted.
What is the fan-out on the clock and chip select pins to the serial scan chips. If these are wired in parallel across many boards, then this could be your problem. With large numbers of parallel connections, you get signal reflections on these lines. This causes some parts to see multiple chip selects and or multiple clocks. Only short term solution is to place RC filters on each line on each board and then slow down the data transfer rate to account for the filtering.

Banjo write

Only short term solution is to place RC filters on each line on each board and then slow down the data transfer rate to account for the filtering.

Can you explain me some example of value for component on RC filter and implementation,

In my display I use two power level, one is 5V for led dot matrix (main micro is atmel 89c2051, and I use max7219 led display driver (11)), and 12V for 4 digit clock with big 2,3" seven segment display.


regards

Are you using eleven MAX7219 in a chain? If so, are all the devices getting corrupted or only some of them? Are they all on the same board or on multiple boards?

The RC filters consist of a resistor and a capacitor in series. This series configuration is attached from the signal pin to GND. Separate RC filters are attached on CLK, CS and DATA. The value of the capacitor is typically about 0.01uF. The capacitor value should look like an AC short at the frequencies that the ringing is occurring at.
During the ringing interval, the capacitor looks like a short and the line is terminated by the resistor portion. Ideally, you would want the resistance to be equal to the characteristic impedance of the line. Unfortunately, with multiple parallel connections and with cabling and probably non-controlled impedances on the PCB, this value cannot be obtained. Assume that the termination should be between 50 ohms and 100 ohms. Therefore, assume 75 ohms. Multiply this 75 ohm value by the number of parallel connections and use this value as the series resistor.

For example, if I had five boards, then 5 * 75 = 375 ohms. I would start wth 330 ohms and 0.01uF in series. I would solder this series connection at the entry point of the signals entering each board.

This does slow up the edge rate of the signals. Therefore, you may have to slow down the serial data transmission.

If this does not help, then you need to start doing experiments to track down where the problem is coming from. Can you alter the code to drive only a couple of the digits and see if that works? If so, then it could be a power supply current issue.

Did the unit only start failing when installed at the customer site? If so, then perhaps the problem is noise being coupled into the serial data stream from an outside interference source. If this data is transmitted on cables, try using shielded cables.

Hi,
I use 11 x max7219, on 3 x 3 boars and one board with 2 x.
Corruption is manifest with going off for example 8 display and another 3 is ON with all 64 leds.
I will try your's sugestion,
thanks,
regards