But how does the circuit know which LED is under the pen? Good old fashioned matrix scanning is the answer ... signal up to a reasonable level for an Arduino Uno to detect.

The rows are turned on and off using ten transistors controlled by ten more Arduino pins. Scanning at 80 frames per second he gets a nice, flickerless display. To make both the LED matrix circuit ...

WiFi’s LED matrix The on-board 12 x 8 (96pixel) matrix of red LEDs (photo right) is Charlieplexed for pixel-level addressing. Arduino_LED_Matrix API is available for programming and control, and “we ...