planar-EL512.256-H/README.md

# 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](https://github.com/adafruit/Adafruit-GFX-Library)
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
build cleanly; the signal timing has not yet been checked on hardware. 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](docs/datasheet/EL512.256-H3%20FRB.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](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/](docs/datasheet/EL512.256-H3%20FRB.pdf)) is the source of
truth; if anything here disagrees with it, the datasheet wins.

## Layout

```
platformio.ini        build config (esp32dev, Arduino, Adafruit GFX)
include/pins.h        pin map
src/main.cpp          test sketch: test pattern + text
lib/EL512/            local library
  src/EL512Panel.*    framebuffer, row encoder, I2S DMA refresh
  src/EL512_GFX.*     Adafruit_GFX subclass
test/                 unit tests (placeholder)
docs/                 datasheet and notes
```

## Build and flash

Requires [PlatformIO](https://platformio.org/) (CLI or the VS Code extension).

```bash
pio run
```

```bash
pio run -t upload
```

```bash
pio device monitor
```

## Using the driver

```cpp
#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](docs/README.md) for design notes and the plan.