Ever wondered about what's behind large advertising billboards? Interested in pretty blinking lights? Curious about electronics and circuit board design? This talk might be for you! Our hackspace recently got a donation of ~800 LED matrix panels (squares with lots of tiny LEDs on them), with little in the way of documentation. I'll explain how they work, how we got them to light up and display things, and how to make it fast enough to display 30fps video -- all with commodity parts that cost less than 20 pounds. We'll explore the weird and wonderful world of poorly translated datasheets and control software, marvel at the library of weird glitched-out images I ended up with on the road to success, and dive into the strange but extremely useful Programmable I/O block of the RP2040 microcontroller. If the stars align, you'll be able to see everything working on a real demonstration panel, too! Although we'll be going into detail on some bits, this talk should be accessible to most audiences.