This display is based on an 9*9 green LED Matrix. The display is driven just with one Arduino board (Duemilanove in my case).
Why do we use a matrix and we don't light's up the leds individually?
A led have 2 pin's: anode & cathode.
So even we put the led's with the common cathode, we will still have 81+1 pin's, the arduino board isn't enought for this.
In a matrix we can put the columns to the cathode and the rows to the anode of the Led's, so here we will have just 9+9 pin's, better then the other but a little tricky on the programming stuff.
Step 1: Basics
- 81 green LED's (or other color)
- an test PCB
- and an arduino board
next we need the schematics :
I have build the matrix like next :
- the columns have the cathode's of the LED's
- the rows have the anode of the LED's
Arduino Pin's :
Now we will have to connect the matrix to the arduino board :
the rows :
- the row 1 to digital pin 0
- the row 2 to digital pin 1
- the row 3 to digital pin 2
- the row 4 to digital pin 3
- the row 5 to digital pin 4
- the row 6 to digital pin 5
- the row 7 to digital pin 6
- the row 8 to digital pin 7
- the row 9 to digital pin 8
the columns :
- the column 1 to digital pin 9
- the column 2 to digital pin 10
- the column 3 to digital pin 11
- the column 4 to digital pin 12
- the column 5 to analog input pin 0 (there is no problem we can use it like a digital one, i'll show you later)
- the column 6 to analog input 1
- the column 7 to analog input 2
- the column 8 to analog input 3
- the column 9 to analog input 4