RetroText

Version 1.1, Aug 2025

Beautiful Blocky Retro Display

An old pinball machine, an industrial control panel, a scifi computer - these are all where you would expect to see warm glowing chunky pixel displays that overcome the low-resolution limitions with somehow recognizable characters.

The RetroText PCB offers six 4x6 character cells, spaced just so. Driven by a IS31FL3737 LED driver, it offers fast updates and 265-levels of brightness per-pixel. A simple 3v3 I2C 4-pin interface makes talking to microcontrollers easy.

Each PCB module wires up 144 retro orange 0402 SMD LEDs, arranged into 4x6 sections. The I2C address can be selected using a soldering jumper on the back of the PCB. There are 4 possible addresses: 0x50, 0x5A, 0x5F, 0x54. Up to four modules can be daisy-chained together, which can display 24 characters at once.

The backside of the board has I2C pads that allow the boards to be soldered together. Here's a photo of the backside and a closeup of the I2C address jumper.

Here's a delicious closeup of the IS31FL3737 LED driver.

RetroText Firmware

The firmware is developed in CPP using PlatformIO. The example works with the ESP32-Dev board, but can be adapted to other microcontrollers that support I2C.

There are 4 modes of operation:

• Modern Font - smooth scrolling, modern font
• Retro Font - pixel-perfect scrolling, retro font
• Clock - display the current time and date
• Animation - display a meteor animation with parallax stars

The main loop is in src/main.cpp. The display is managed by the DisplayManager class in src/DisplayManager.cpp. The fonts are defined in include/fonts/. The messages are defined in include/messages.h.

Minimal Example

Here's a simple example that displays a message on a single RetroText PCB (6 characters wide):

#include <Arduino.h>
#include "DisplayManager.h"
#include "SignTextController.h"

DisplayManager* display = nullptr;
RetroText::SignTextController* sign = nullptr;

void setup() {
  Wire.begin();
  Serial.begin(115200);

  display = new DisplayManager(1, 6, 6);  // 1 board, 6 characters, 24w x 6h pixels
  display->initialize();

  sign = new RetroText::SignTextController(display->getMaxCharacters(), display->getCharacterWidth());
  sign->setFont(RetroText::MODERN_FONT);
  sign->setScrollStyle(RetroText::STATIC);
  sign->setMessage("Retro!");
  sign->setDisplayManager(display);
}

void loop() {
  sign->update();
  delay(20);
}