An Arduino gives this quirky old LED sign a new life as a smart display

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.

The second task was programming new messages. Mayer thought he’d be able to send data to the display’s controller via serial, but wasn’t able to get that working. Attempts to communicate didn’t result in a response from the display.

However, the display did come with a PS/2 keyboard and some intriguing instructions. It turns out that the display’s controller accepts input directly from the PS/2 keyboard, which is quite unusual. But it gave Clem an access path: he used an UNO R4 WiFi board with a PS/2 library to emulate keyboard input. As long as it “types” slowly, the Arduino can program the display with any arbitrary message.

And because it has Wi-Fi capability, Clem can make the Arduino work via his network. It would, for example, be possible to have the Arduino check the weather each morning and then program the display with a weather description.

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