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Runs a 9600bps "server" on the Sparkfun LED Matrix backpack to control from a "real computer"
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Makefile
README.md
block_sender.c
led_sender.c
led_sender.hex

README.md

rgb-backpack-controller

Runs a 9600bps "server" on the Sparkfun LED Matrix backpack to control from a "real computer"

LED Matrix

Set up

(If it's not an arduino already)

  • Get some way to ISP program an Atmel if it's not an arduino already, like one of these
  • Put the ISP 6 pin cable of the programmer so that the ribbon cable goes away from the board
  • Get this arduino boot firmware
  • Program it to the board via your ISP using avrdude:
avrdude -V -F -c stk500v2 -p m328p -P /dev/cu.usbmodem26211 -b 57600 -e -u -U lock:w:0x3f:m -U efuse:w:0x05:m -U hfuse:w:0xda:m -U lfuse:w:0xff:m
avrdude -V -F -c stk500v2 -p m328p -P /dev/cu.usbmodem26211 -b 57600 -U flash:w:ATmegaBOOT_168_atmega328_pro_8MHz.hex -U lock:w:0x0f:m

Controlling the matrix from anywhere

  • Hook up a serial connection between your atmel/arduino and whatever you want to control the LED Matrix from (since I'm using a Beagleboard, the serial port is already connected to the trainer as /dev/ttyO1)
  • Flash led_sender.hex anyway you know how. Since I put that firmware on my board above, I do this quickly after hitting reset:
avrdude -V -F -c stk500v1 -p m328p -P /dev/ttyO1 -b 57600 -U flash:w:led_sender.hex 
  • (You can of course compile led_sender.c yourself if you want, i put the avr-gcc makefile in the repo too. But you shouldn't need to change it unless your pin numbers are different.)
  • On the computer you want to control the LED Matrix from, change the serial port name in block_sender.c
  • Compile the block_sender.c:
gcc -o block_sender block_sender.c
  • Run the block sender on the computer you want to control the LED Matrix from
  • It should look like this (in real life it's less blown out)

alt text

  • Now control your LED matrix at will. In block_sender you can see how it's done -- you fill up a char array with 64 bytes, each one a 4 bit number corresponding to the palette index. Then you call
draw_frame(fd, frame);
  • Lower level if you want: the atmel listens for bytes on the UART at 9600. Every time it gets a byte, it checks if it is 32. If it is, it starts the drawing pointer at position 0. If it's not, it splits the byte up into two 4-bit numbers, each one a palette index. After drawing two dots it incremements the position automatically. So you should send 33 bytes per frame, starting with the number 32 and then 64 pixels, each 4 bits.

FAQ

Why didn't you just use SPI, isn't it a waste to have 2 microcontrollers converting stuff back and forth

Have you tried to use SPI on a computer before, so annoying

Can I increase the baud rate?

Probably. The UART might get in the way of the SPI. I haven't played with that too much and 9600 is fine for what I need right now.

Can there be more colors?

Yes -- my protocol kept it at 4 bits but you could change that. There's not too much variation in the colors and some of them flicker a lot, so I kept it safe. They are, in order (RED is 1, DKRED is 2, etc)

// My lovely palette. 15 colors. RRRGGGBB
#define CRC     0xF0 // should never be
#define RED     0xE0
#define DKRED   0x40
#define ORANGE  0xE8
#define YELLOW  0xFC
#define GREEN   0x1C
#define DKGREEN 0x0c
#define TEAL    0x5E
#define LTBLUE  0x1F
#define BLUE    0x07
#define DKBLUE  0x02
#define PURPLE  0x46
#define PINK    0xE3
#define WHITE   0xFF
#define GRAY    0x4A
#define BLACK   0x00
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