Planar EL512.256-H on ESP32

Drive a Planar EL512.256-H (512 × 256, monochrome electroluminescent) panel from an ESP-WROOM-32 (classic ESP32), with an Adafruit GFX compatible driver so the usual drawing, text and font APIs work.

The panel has no frame memory and needs a continuous video stream. The ESP32's I2S0 peripheral in 8-bit parallel (LCD) mode streams a precomputed frame from DMA, so the CPU is free while the panel refreshes.

Status: framebuffer, GFX layer, row encoder and I2S/DMA refresh are implemented and run on hardware: the panel shows a correct image (VCLK 5 MHz, HS and VS checked with the ESP32's PCNT). Updates are not yet tear-free.

Hardware

• ESP-WROOM-32 dev board (esp32dev)
• Planar EL512.256-H, configured for two-bit parallel mode: jumper 2 (DCONFIG) of pin strip PS1 removed, jumper 1 (SELFTST) fitted (datasheet Table 3)
• Datasheet: docs/datasheet/EL512.256-H3 FRB.pdf
• Check the panel's logic-level and supply requirements in the datasheet before wiring.

Wiring

Panel signal	Panel pin (Table 1)	Function	ESP32 GPIO	DMA byte bit
VCLK	J1-13	Video clock, data latched on rising edge	18	I2S0 BCK
VID	J1-15	Pixel data, even columns (x = 1, 3, …)	19	0
TVID	J1-7	Pixel data, odd columns (x = 0, 2, …)	21	1
HS	J1-11	Horizontal sync	22	2
VS	J1-9	Vertical sync (rising edge used)	23	3
ENABLE	J2-6	Display enable, low = off	25	—
_LOWPWR	J2-5	Low-power mode, low = on	26	—
GND	J1-6, 8, 10, 12, 14, 16	Signal return	GND	—

The datasheet numbers columns 1 to 512 from the left; x in the code is 0-based, so x = 0 is column 1 (odd, TVID).

Power (Table 1, Table 4): Vcc1 +5 V logic on J1-3, 4 (4.75–5.25 V, 0.2 A max); Vcc2 +11…+30 V on J1-1, 2 (0.9 A max at 12 V). J1-5 is reserved: do not connect.

The panel inputs are HCT compatible with internal pull-ups of unstated voltage, and the ESP32 is not 5 V tolerant, so drive them through a 74HCT245 or 74AHCT541 powered from 5 V (see the plan). ENABLE is pulled high inside the panel, so the panel scans while the ESP32 is still booting and VCLK is not running yet; add a pull-down (for example 10 kΩ) on the buffer's ENABLE input so the panel stays off until begin() starts the stream. Keep the cable under 300 mm, or add 47 Ω series resistors for up to 2 m.

The pin map lives in include/pins.h.

Timing

Parameter	Value	Datasheet limit (Tables 5, 6)
Pixel clock (VCLK)	5 MHz, 2 pixels per clock	30 MHz max, keep running
HS high (T7)	256 clocks	256 in two-bit mode, even
HS low (T6)	16 clocks	4 clocks min
HS period (T8)	272 clocks = 54.4 µs	50 µs min
Lines per frame	261 (256 visible + 5 blanking)	256 rows + T1
Front porch (T1)	220.8 µs (last row end to VS rise)	100 µs min
Refresh	5 MHz / (272 × 261) ≈ 70.4 Hz	70 Hz typ, 75 Hz max

The datasheet (docs/datasheet/) is the source of truth; if anything here disagrees with it, the datasheet wins.

Layout

platformio.ini        build config: envs still_alive (default) and esp32dev
include/pins.h        pin map
src/still_alive/      Portal-style end-credits demo (env still_alive)
src/test_images/      test sketch: cycles through 12 test images (env esp32dev)
lib/EL512/            local library
  src/EL512Panel.*    framebuffer, row encoder, I2S DMA refresh
  src/EL512_GFX.*     Adafruit_GFX subclass
tools/                import_still_alive.py
test/                 unit tests (placeholder)
docs/                 datasheet and notes

Build and flash

Requires PlatformIO (CLI or the VS Code extension). The upload and monitor port is set to COM20 in platformio.ini.

pio run -e still_alive -t upload   # end-credits demo
pio run -e esp32dev -t upload      # test images
pio device monitor

Still Alive demo

A recreation of Portal's ending: timed song text typed into a console on the left, credits scrolling top right, ASCII art bottom right. The text, timing, art and credits in src/still_alive/imported.h come from SDSkyKlouD/still-alive-web and can be regenerated with:

python tools/import_still_alive.py
pio run -e still_alive -t upload

Without imported.h the demo plays placeholder text. Reset the board and start the song when the serial log says (7.75 s after reset with the imported data).

Disclaimer: "Still Alive" was written by Jonathan Coulton for Portal (2007). Portal, its credits and ASCII art are © Valve Corporation (see Valve Legal Info); the web recreation they are imported from is by SD SkyKlouD. They are included only for personal, non-commercial use in this hobby project, and all rights remain with their owners. This project is not affiliated with or endorsed by Valve.

Using the driver

#include <EL512.h>
#include "pins.h"

EL512Panel panel({el512pins::VCLK, el512pins::VID, el512pins::TVID, el512pins::HS,
                  el512pins::VS, el512pins::ENABLE, el512pins::LOWPWR_N});
EL512_GFX display(panel);

void setup() {
  display.begin();
  display.setTextColor(1);
  display.print("Hello");
  display.display();   // push the drawing buffer to the refresh stream
}

See docs/README.md for design notes and the plan.