Continuing the Minimum Viable #Postcard (#MVP) project, this just arrived from the USA, measuring 76 by 128mm (3 by 5 inches), and sent on the 25th of September. #postcrossing
The message on the back asked about how to build a #XOR gate out of #diodes. The answer was too big to fit on a postcard, but see https://electronics.stackexchange.com/a/322168