For the LED Matrix we want to build on the CCCamp2007 we decided to design our own LEDMatrix Controller/Driver setup. It will consist of two parts.
LED Matrix Driver Boards
Our Matrix should have a resolution of 48x72 pixels. So there will be 48 rows and 72 columns. The basic building block of our ledmatrix will consist of an 8x8 pixel module (or 8x48 or 8x76 depending on the levels of grayscale steps you want).
for our matrix we need 6x9 = 54 modules.
So how is such basic building block connected? The cathode (GND) pins of all LEDs in each of the 8 rows are connected to each other. Also all the annode (+) pins of all lesds in each column are connected. Sowe get 8 rows and 8 columns. each column intersects each row and the intersections are the leds. To lighten up one specific led we have to set the row the led is connected to to GND and the column to +5V (we also need a resistor to limit the current). TODO: das besser erklaeren rasteransteuerung etc.
The 8 rows are each connected to a powermosfet and are driven to ground one at a time (so the matrix is 8times multiplexed). For driving the mosfets we use 2x Quad-mosfetdriver which in turn are controlled by a 8bit shifting register.
For the columns we take almost the same components except that we don|t need the mosfets. the mosfet drivers (which consists of mosfets of course - in fact its a half bridge and so contains one pMOS and one nMOS FET) are strong enough to drive a high current led with a constant current of 0.5A and peak currents of 1.5A
Likewise all the annode (+) pins of all LEDS in a column are connected together and are driven by a constant currentsource (I could not find a shifting register that can sourcer more than 20mA this suxx)
chips that might be usefull for this
- Texas Instruments
- On Semi
FPGA LED Matrix Controller
an FPGA producing the correct signals to drive the above driver module, or drive many modules in paralell :) for each module we need 3pins