An Arduino gives this quirky old LED sign a new life as a smart display — April 7th, 2026 Clem Mayer over at element14 Presents got his hands on a big old LED matrix display and when he turned it on, it worked perfectly. It even displayed the last programmed message, like an inadvertent time capsule. But upon opening up the enclosure, Mayer found danger and some strange control quirks. So, he used an Arduino UNO R4 WiFi to rebuild the LED sign , making it both safe and usable. The danger lurking inside was thanks to a brick-style AC-to-DC adapter. That wouldn’t be a problem on its own, but the AC input wires were soldered directly to the adapter’s pins. That’s a big no-no, because a loose wire could contact the enclosure and send deadly voltage through it for anyone to touch. Mayer’s first task was to replace that with a simple and correctly wired external power supply that outputs a safe 5V DC. That was easy and wasn’t particularly interesting, but it was absolutely crucial for peace of mind.…