8 x 32 LED "shield"

My 8x32 “shield” :grin: is alive!
Simple design - 4 x MAX7219 wired to 4 8x8 LED matrixes. MAX7219’s wired up as 4 SPI devices (not daisychained).
Set up the board so I could move 2 matrixes and play with 16x16 later on, just duplicate the wires for 2 of them.

Took me a while to realize I hadn’t wired up power & gnd to 3 of the MAX7219s, so they were really dim! Must have got distracted when wirewrapping the last little bit.

Had also messed up writing the 8 bytes to each display out.
Format had to be

for (1 to 8){
ss low
register address
data byte
ss high

and I wasn’t quite there, last } in the wrong place so the ss high wasn’t occurring after 16 bits

Day off tomorrow, can check out receiving a serial byte and making it show up …

MVI_2451.AVI (3.05 MB)

Love it Crossroads... maybe they should call you "The SPI King"

why drive a Dodge Dart when you can drive a Camaro I say 8)

Exactly 8)

Why didn't you want to daisy chain them?

Didn't want to have to send out 4x the data every time when I could make it faster by going direct.

Alright, had to rewire the matrices. Managed to misread the datasheet and put the MSB into the LSB row of LEDs, and get them turned 90 degrees to boot.
Here’s a short test run - working across digit 7 to 0 and lighting up bit 7 to 0 of each digit. Didn’t take long to rip it out & rewire after I figured out what had happened.
Just lef the original pins there and added another set of sockets.
Still planning to move the outer left & right display down to the middle and play with 16x16 matrix later on, hence the extra sockets at the bottom.

And a pic of the wirewrapping of the back.
I’m thinking maybe this would make a nice little board to build up into larger displays - 8x8 with MAX7219, and 5 IO pins- +5, Gnd, Data in (2 pins), Data out, SCK (2 pins), MOSI (2 pins), CS (2 pins). Can wire up as daisy chained units, or as parallel units with unique chip selects like I have here.
http://www.crossroadsfencing.com/BobuinoRev17/Test_movie.AVI (8M, and only 13 seconds - can’t seem to select lower file size setting with my Canon power shot camera)

Scrolling text won’t be long now!

Quick question if I may,

are those matrices bi or tri colour because I notice that you are not using all the matrix pins ?

I suppose we can soon expect to see super fast SPI RGB/ or RG displays in varying matrix configurations :D

Hi CrossRoads!

Very interesting!!! XD

Where can I buy a large PCB? :astonished:

@Pedro ,they are orange/green, 24 pins. I didn't realize that when I started this; in fact I only realized it after I wired the first one on & saw that I had wired all 16 pins from the MAX7219 and there were still pins left on the matrix. I think the parts were mismarked and sold off cheap, a friend found them at an electronics fleamarket and picked up several tubes (6 or 8 per tube?) for like $1 or $2 for the entire tube. I had drawn it up per the data sheet we found for the part number marked on the side (16 pins, A5880SRSG-A; found a few datasheets for A5880 and used that draw the design)); then several days later put sockets based on the pins on the parts (24 pins) without looking at the schematic, thinking more about a layout where I could cut the board in half lengthwise, then deciding not to & planning for a 2x2 configuration as a 2nd test scheme (the extra sockets below the middle 2 displays will be paralled to the outer 2 and the displays moved down); then several days later started wiring and discovered the mismatch. Looking the parts over I saw what looked like another part number in the artwork for the matrix, and that turned out to have a schematic/pinout that matched the board, confirmed my testing a bunch of pin pairs with 5V & a resistor.

I am only using 1 color for now. Maybe add 2nd color at a later date.

@Deafboy, its a 18cm x 30cm board. I got it here http://www.dipmicro.com/store/PCB-UNI30H Search "18cm 30cm prototype" on e-bay, they are available for ~$5 USD and less for 5-lots.

Next step in the software is done - scrolling text!
You can see it in action here.
Its setup to accept up to 233 characters via serial interface.
Can use the + < > keys to stop the message and manually scroll back & forth, then = to get it going again.
Working on getting \ to delete characters from the end.
Then will add storing to EEPROM for PC less demonstration.
And thinking about ways to add a remote after that - RF keypad perhaps.

Storage to EEPROM is working - needs tweaking tho. Seems to just write from where its called corrupting the message being displayed. Also not reverting to serial input correctly, so the storage logic needs some work. Fun stuff! Stopping scrolling, moving back & forth 1 character, restarting is working pretty well. Too easy to get the start pointer past the end pointer and display some nonsense output, so that needs work as well Getting there tho.