Currently one short movie to give a quick impression of the project. The basic concept is to build the four-on-a-row game. We did this by building a 2color 2D martrix using red and green SMD LEDs. The matrix is driven directly by an Arduino Mega without any addtional driver ICs. WIll update with a step by step explanation when the jam is over

Step 1: Solder the LED Matrix

Use red and green SMD leds, or RGB leds. Solder them on a two-sided perforated PCB. Make an 8x8 matrix of red and green leds

The cathodes are connected together to COL A (column A, not the drink). The anodes are connected to ROW A and ROW B. You can use ULN drivers, or generic BC547 and BC557 transistors. We use transistors, the Arduino drives the base through a resistor of 1K. The transistors of the two rows drive the leds through a transistor of 220ohm, for a current of 20mA. You can use higher currents because the brightness drops during the multiplexing cycle. If you turn on the led for too long, you risk burning it.

The photos below indicate the way you solder the leds. Be patient :-)
On the front side, solder the cathodes together.
On the back side, use tape to isolate the cathode columns and unused islands. Then solder the anodes together.

Step 2: Solder Score Matrix and Buttons

The score matrix is soldered in a 8x2 matrix in the same way as the 8x8 matrix, but leave some more spacing between red and green leds. The anodes are driven directly by the Arduino, the cathodes are driven by a transistor.

Solder the 4 buttons. These connect the Arduino pins to the ground