Earlier this year I found a number of flexible LED matrix panels that I've been using in my clothing and accessories. The panels communicate via bluetooth from an Android app but I wanted to be able to sychronise multiple displays and control them locally from a small Arduino without Bluetooth.
I wrote this library so you can communicate using your own code with these displays. I've tested it with both a RGB display (32 pixels by 16 pixels by 7 colours) and the mini single colour display (48 by 12 pixels). Sometimes these single colour displays have blocks of different colour LEDs so they look multicolour even though they are not.
Download the release and import the Zip in the library manager
There are a number of sellers of these displays on various marketplaces, and they come and go quite often. You can usually figure out if any given display will work with this library by looking at the app they ask you to use. If the app is LED1248 (sometimes called COOLLED1248) it should work. The boards are relatively inexpensive (US$15-US$30) and are sold bare and as part of clothing, hats, and even dog collars. A good way to get one if you are in the USA/Canada is from Lumen Couture
The displays come with a little dongle that provides power (3v from a lithium battery) and communication to the flexible panel. The dongle doesn't do much processing, it just provides the power on and off commands and passes through any other commands recieved by its bluetooth module. This means that via the serial interface you don't have full addressable control of the LEDs but instead can do the same sorts of things as the app does. You can display some text (scrolling it if you like), display a multi-frame animation, or do a music-style bargraph.
Unplug the dongle from the board (sometimes they have connectors, sometimes not) and connect the power (3v), ground, and TX pins to an arduino (I used a Trinket M0 but anything should do as long as it runs at 3v, has hardware serial pins and enough RAM for any animations or bitmaps you want). Do look at the label on the PCB for which pin is which and don't trust the wire colours (one of the boards I received has the red wire as 0v, black as 3v).
Note: This library doesn't use the RX pin and relies instead on timing for knowing when to send the next command. Firstly this saves connections, useful especially on wearables, but also the RX isn't actually UART serial data so we'd have to parse it.
This library should also work communicating over Bluetooth to the boards, but you need to batch the bytes you send into groups of 20 bytes max, and you will likely want to handle the return acknowledgements. Pull Requests with patches welcomed!
By using the Adafruit GFX canvas library you can draw text and other objects onto a canvas then push it to the board to display.
The included example displays a demo reel: a 5 frame animation with some text, some scrolling text, and then a random bargraph display.
I joined three white displays together and slid them between two glued layers of latex sheeting. The top layer was 0.5mm semi transparent black, the bottom 1.05mm black. LEDs shine quite well through some latex, but you need to experiment to find colours that don't affect the brightness or filter some of the colours too much.
Testing the latex sheeting:
The final headband made from 3 LED matrix strips
