unusual-thoughts/8x8matrix

Backpack for 8x8 RGB LED matrix

Backpack for 8x8 RGB LED matrix

This is a simple breakout board for 8x8 RGB matrices like the GTM2088ARGB
It uses a TLC5947 that provides 24 12 bit current sink PWM channels, and a 74HC138 3 to 8 line decoder followed by P-channel MOSFETs to drive the rows.

The needed Eagle libraries are in eagle-lbr/
The whole thing fits on a single layer PCB.
The matrix is controlled through the 9-pin header with this pinout:

Pin number	Label	Description
1	A2	row higher bit
2	A1	row middle bit
3	A0	row lower bit
4	SIN	TLC data (24x12 bit = 36 bytes)
5	SCLK	TLC clock
6	BLANK	TLC blank columns and reset PWM timer
7	GND	Ground
8	VCC	+5V
9	XLAT	TLC latch data

To get everything to fit on a single sided board, I had to make weird column and row assignments:

A0	A1	A2	Row Number
0	0	0	2
0	0	1	1
0	1	0	0
0	1	1	7
1	0	0	4
1	0	1	5
1	1	0	6
1	1	1	3

TLC channel	Columns
0-7	Red 0-7
8-15	Blue 0-7
16-23	Green 7-0 (inverted order)

The arduino-lbr/ directory contatins a modified version of the Tlc5940 library by Alex Leone, named Tlc5947. Like its counterpart, it can use arduino hardware spi to speed things up to an acceptable refresh rate. The basic bitbang code flickers quite a bit, even with direct port manipulation.

The arduino/ directory contains a demo arduino sketch using that library.