I spent some time looking for basic requirements when using this module. Couldn't find anything.
Here's how I got a display in working order. It needs some tweaks to work well.
Not sure where to post this kind of info. Feel free to repost it or remove it.
Hope this helps those using this module.
8x8 LED max7219 fc-16 hardware modules
What I like about these modules is that they provide a display that
can be seen from a distance. But there are a couple requirements
to get them working well. I'd always use an external power supply.
There's 64 LED's in each matrix. If they draw 10ma each, that's a
total of 640ma for only one matrix when every LED is on. They need
a power supply for reliable, consistent operation. It's not optional.
Just spent a couple hours sorting out hardware issues on these.
They are picky about ground connections. And they need filter caps.
I will not spend any time to isolate every detail of their operation.
In any case I would recommend soldering an electrolytic filter cap
across Vcc and GND at the top of each module. At least 1uF, or
larger. I used what I had on hand. It's a prototype. Max7912
drivers generate switching currents when driving LED's. Filter caps
help reduce voltage spikes that will interfere with control signals.
Random and intermittent operation results without them, depending on
how many LED's are being driven.
These two requirements are not optional for any hope of hardware
stability. What follows is not as critical.
I soldered all connectors across a 10 matrix display. Vcc and GND
were all soldered with separate leads to an external power source.
Each module has its own Vcc and GND lead to the power source. These
are NOT wired in series like the original configuration. Parallel.
Signal wires (3) must be connected in series from the bottom of one
module to the top of the next module. This is standard configuration.
I soldered all of these connections. DIN, CS, CLK.
Then, all the bottom Vcc connections are left open and all bottom
GND connectors are soldered to a single wire, in series, which is
then connected to an UNO GND pin.
Since making these mods, hardware issues are resolved. There are
probably other ways to address hardware issues, but these mods work
well for me.
MaxMatrix code has to be edited when writing to more than nine
modules. At least for the revision that I found online. Everywhere
there is an '80' or '81' in the .h or .cpp file I changed to a
value of '88'. It now writes to ten modules connected in series.
If you add more modules, keep increasing these numbers until it
writes correctly. I did not go through all the code, so I can't
say how this works, exactly. There's almost no comments in the
code, and I don't want to spend any more time on it.
I have not had any trouble working with my display since making these
mods. I'm using a total of ten (10) FC-16 modules.
There's no substitute for a soldering iron. And I might add a
resistor here and there in signal lines if any other hardware issues
crop up. It's always a good idea to add current limiting resistors
on all signal pins/ports of your Arduino. There's nothing quite like
stable hardware, and it's seldom mentioned. (I see these issues quite
a bit watching youtube video.) It makes coding that much easier.
Again, I really like these modules for a display. They just need a
little help to get them working well. It's hard to complain about
price, and there's a number of ways they can be configured for
display purposes -that you can see across the room-. 64 outputs for
each matrix. In combinations, many more than that. Kinda cool.
Then, there's SPI applications... Later.