I made a custom message LED badge made in response to the Star Simpson controversy. Star was a student in our group and got a very unfair treatment by the authorities, the media and MIT when she accidentally wore an electronic badge in the Logan airport.
I made an array of 36 orange LEDs, found an AVR that had four I/O ports (ATmega32) and and used a 3:8 mux. The mux was necessary because 4×8=32 but I needed 36 pins to control all the LEDs.
To reduce the size of the board, I used the same current resistor for all LEDs, to make sure that the power rating for the resistor wasn’t exceeded only one LED is on at any given time.
I also milled two circuit boards using the mini mill and attached them using standard 0.1m headers. This effectively gave me a 2-layer board.
The badge can spell out any message, in the attached video it spells out “socket to me” because that was the message Star Simpson used, I have also had it spell out “fab class” amongst other things.