Who needs a 1920×1080 OLED display when you can have an 8×8 matrix of LED goodness? That’s the question [Kathy] asked when she built this LED matrix light pen project. It looks simple enough – a 64-LED matrix illuminates as the pen draws shapes. But how does the circuit know which LED is under the pen? Good old fashioned matrix scanning is the answer. Only one LED is lit up at any time.
[Kathy] used a pair of 74LS138 3-to-8 line decoders to scan the matrix. The active low outputs on the ’138 would be perfect for a common cathode … Read the rest