How Many Hacks in an LED Display?


There are so many nice hacks in [Joekutz]’s retro LED display project that it’s hard to know where to start. There’s his DIY LED display controlled by an Arduino UNO. To have some text or picture for the display, he’s wired the output of a Bluetooth speaker directly to the Arduino, and sends it speaker tones that encode the text to draw. And as if that wasn’t enough, he’s hacked a quartz driver board from an analog clock to use the display as a clock as well.

Let’s start with the LED matrix display, perhaps the best excuse for trying your hand at shift registers. This display uses two such 8-bit shift registers daisy chained together feeding two 8-bit Darlington arrays. The display has ten rows of sixteen columns, and you guessed it, the columns are controlled by the sixteen shift registers. Two Arduino pins tell the shift registers which column to turn on. The rows are turned on and off using ten transistors controlled by ten more Arduino pins. Scanning at 80 frames per second he gets a nice, flickerless display.

To make both the LED matrix circuit board and the control board, [Joekutz] carved out isolation paths in copper clad boards using his homemade CNC mill. Be sure to check out the first video below to see his misadventures with it that ultimately led to his gorgeous boards.

Tones sent to the Arduino
Tones sent to the Arduino

The Arduino draws to the display, but why not tell it what to draw from a laptop or phone? To do that he paired a cheap Bluetooth speaker with his laptop. On the laptop he made a simple webpage with which he can draw pictures or write text. Clicking on a button labelled “Beam!” on the webpage runs some javascript that converts the pictures or text to tones. An AudioContext object then sends those tones to the paired speaker.

To get the tones from speaker to the Arduino, he hacked the Bluetooth speaker’s circuit board, redirecting its output to an Arduino analog pin. See the second video for his adventures in figuring out a way to encode those tones such that the Arduino can decode them and turn them into something for controlling the LED display.

And lastly, since he has a display, why not use it as a clock? He found that the Arduino’s internal clock wasn’t precise enough, so he bought a cheap analog clock and removed its quartz motor driver board. With some minor modifications, and a transistor to amplify the signal, he used the timing signals to keep his Arduino clock program’s time accurate.

While individually these hacks of [Joekutz]’s were enjoyable, seeing them all combined in one package seems like too much fun.

DIY LED displays are not new here on Hackaday. Check out this colossal one, aptly name Colossus, with 1250 LEDs in two square meters. Clocks also seem to be a favorite and we’re constantly surpised by the novel ways people come up with to display them.



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