Driving video wall panels. (including free test software)
It turns out that the video wall panel used in the TV series Project MC2 merchandise is actually a standard 75hub LED video wall module.
These modules are “dumb” in that they require a continuous stream of data being updated and scanned at high speed to create an image. This is quite an intense processor load, so these modules are usually used with dedicated drive cards that can receive image data and then output it at high speed to a grid of these panels.
Having identified the chips on the back of the PCB and sussed out how they might be driving the LEDs I attached a PIC microcontroller and wrote some software to drive the panels.
Initially I wrote a simple routine to display a single line of a single colour. The usual “Hello world” test to see if I had deduced the drive system correctly.
I then wrote a bit of software that can test the panels completely using a single microcontroller (PIC16F627A) with no other additional components other than a standard 100nF decoupling capacitor across the power pins. The same 5V supply used to power the panel can be used to power the test circuitry.
It starts by testing all the LEDs by displaying a full-panel colour sequence of red, green, yellow, blue, magenta, cyan, white and then a set of colour bars. Then it tests the output enable pin of the module by toggling it while displaying two lines of white LEDs which will flash if output enable is working. The microcontroller then tests the row drive MOSFETs by stepping through each line in turn on the top and bottom halves of the display simultaneously.
You can download the assembly and hex code files for this software with the following link, noting that the hex code can be directly loaded into a blank chip with a PICkit 2 or 3 programmer.
That same link can also be used to find the other test software that generates a continuously scrolling pseudo random pattern of coloured pixels that are dynamically generated in real time by software as each line is loaded during the screen refresh cycle.
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