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76  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 05, 2012, 04:49:04 pm
My code is way too long to post in this forum...could you give me your email possibly and I can send you a schematic capture and my code and see if you can see something I'm doing wrong .....making the LEDs have negative voltage,...
77  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 05, 2012, 04:20:09 pm
Got 3 matrices wired up with 1 to go...heres the issue now.....the 3rd matrix blinks when I power up but then goes out...so I probed the row and its column and I'm measuring negative voltage....????? why is the Max7219 supplying negative voltage to the matrix rows?
78  Using Arduino / LEDs and Multiplexing / Re: MAX7219 and 51 MCU 8x8 LED matrix on: November 04, 2012, 03:52:09 pm
These are SPI Pinouts.....or serial peripheral interface.....on the Uno , you can google uno board and the site has the info there. Cs also can be SS, MOSI is data, SCK is clock.....
79  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 04, 2012, 01:43:08 pm
That's cool. I have an Associate's in computer and electronics engineering from ITT Tech. And just graduated from Devry with my bachelor's in electronic engineering. I'm starting my masters in project management in January.

Ya expressPCB is very simple. The PCB design portion of eagle I'm trying to learn more. The rats nesting of the traces always irritate me.
80  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 04, 2012, 12:08:42 pm
EAGLE is awesome. I sometimes use expressPCB and trying to learn more orCad and altium. I assume you're an engineer? I just graduated with my BSEET but have years of experience, but I just started tinkering with arduino this past year.
81  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 04, 2012, 06:46:37 am
Ok, now I see....you have a point about manipulating a chip. I appreciate your patience. Let me bust out this wiring up job and ill send you pics and video. That looks like EAGLE CAD.....your schematic. Yes?
82  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 03, 2012, 06:59:35 pm
Im confused now trying to understand why you would use MOSI (data) in parallel when the site and datasheet explains to cascade the MOSI.....could you post a quick schematic, or block diagram of what YOU have working please
83  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 03, 2012, 06:48:16 pm
If data out from max7219 isn't interfaced to data in on the next max7219 sequence, are you sure MOSI Will work if its in parallel? All 4 chips sharing the data out from arduino like the SCK does? Look at the schematic in the playground link I posted in my pilot post of this topic.....that's the schematic I've been going by.
84  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 03, 2012, 06:43:51 pm
So bottom line, SS or LOAD is interfaced to each individual chip coming from the assigned ss0-ss3.

SCK needs to in parallel with each chip sharing the same clock output from arduino.

Then the MOSI or data would go from arduino to pin 1 of chip.....pin 24 of chip goes to pin 1 of next chip and so on through number 4 max7219.

If I'm wrong here could you correct me.
85  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 02, 2012, 09:01:02 pm
You may be right.....I usually used 330 for any common anode segment displays, but maybe I will go with at least 1K.....

And one more thing.....MOSI....this is the data pin coming from arduino to pin 1 ( data in) on the first max7219... But then pin 24 (data out) of the first chip would then interface pin 1 again of the next max7219 and so on through #4 . So that technically is asynchronous. the serial clk or SCK is the only Pinout that should be in parallel or synchronous......correct?
86  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 02, 2012, 06:55:22 pm
MOSI and SCK in Parallel...Thats what I needed to make sure of...its this way in the schematics too....

I have 300 Ohm resistors for the I sets (Pin 18) on each of the MAX7219 ....The ss0 - ss3 Will be controlling each individual LOADs....

I placed the 100 nF and 10 uF caps to suppress any of the EMI in the circuit. I also have the code integrated and compiled / verified in 1.0.1 IDE.

just need to solder in each of the 16 pinouts wires from the MAX7219s to each of the Matrices.....

I'll keep you posted....

I noticed you said lower case letters must be used too....  < -------definitely remember that...

in your code though, you have all the HEX codes for each of the letters...is that to define them once they are input from the serial monitor? I thought it would scroll all of those in sequence when I first downloaded and read your code.



87  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 02, 2012, 03:22:21 pm
Kind of wish it wasn't Friday because I have this all at work so two days away from it.......oh well start back Monday.....good thing I can solder well too, this is going to be a rats nest of 28 gauge wire.......ill keep you posted crossroads and take pics n video soon too.
88  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 02, 2012, 02:59:40 pm
Thanks for clearing it up. Ya I'm going to assign ss0-ss3 like I said using 53,49, 48 and 47.
89  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 02, 2012, 02:18:07 pm
So I think it just hit me what you've been trying to say...you don't want the Load or Pin SS to be in parallel coming from the arduino to each of the MAX7219s right? You wanted each MAX7219 to have its own individual LOAD pinout coming from arduino right?

thats why I should do the assignment of  the SS outs like this:

ss0 = 53 // MSB     
ss1 = 49     
ss2 = 48   
ss3 = 47  // LSB 

that just leaves the CLK or (SCK) from the arduino...that still needs to be parallel or (synchronous) right?


and you're saying you open the serial monitor and type in a message and it will display on the matrices?



(I just read your latest post) but I think I'm going to go along with what you have because you digitalWrite SS1-SS3 alot....
90  Using Arduino / LEDs and Multiplexing / Re: Scrolling text on LED matrices using SPI and arduino Mega2560 on: November 02, 2012, 02:03:39 pm
so pretty much what you're saying is I can just leave it as :

byte ss0 = 53    and don't worry about   the 47, 48 and 49 as I mentioned before since its in SPI and my MAX7219s are cascaded?

its like this:

Arduino:

SS -- > (Pin 53 of Mega 2560) -----> Load of ALL MAX7219s (Pin 12) these would be in parallel

SCK -->(Pin 52 of Mega 2560) ----->    CLK of  ALL MAX7219s (Pin 13)  these would be in parallel

MOSI --> (Pin 51 of Mega 2560) -----> Serial Data Out going to the FIRST MAX7219 (Data In ~ Pin 1)   
                                                        Then from there Data out (Pin 24 of MAX7219) to the next MAX7219 Pin 1 (Data In)


and as Long as I connect the colums and rows up correctly to the matrices, the Code and the SPI will do the rest correct?

And also, you said you're typing in the serial monitor what to display on the matrices?


So I have it as

byte ss0 = 53; //MSB  <------- This is the SS output from Arduino Mega and with SPI library it should load the Max7219s


while you have it as:

byte ssOutput = 10;
byte ss0 = 7; //MSB -> easy to plug a header into Arduino
byte ss1 = 6;
byte ss2 = 5;
byte ss3 = 4; // LSB         

But yours aren't cascaded like mine......
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