Initial commit: plasma DMD driver project

- Design docs: 12 V DC power supply, safety and bring-up, ESP32 interface, BOM
- PSU schematic (schemdraw) and KiCad 10 carrier-board project with HV net classes
- ESP32 PlatformIO firmware skeleton with HV watchdog toggle
- Reference schematic of the Stern 520-5138-00 display PSU

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

firmware/platformio.ini

@@ -0,0 +1,5 @@
+[env:wemos_d1_mini32]
+platform = espressif32
+board = wemos_d1_mini32
+framework = arduino
+monitor_speed = 115200

firmware/src/main.cpp

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+// Plasma DMD driver skeleton for Wemos D1 mini ESP32.
+// Scans a 128x32 plasma panel continuously and toggles the HV watchdog once per row.
+// Signal polarities (enable, latch, row data) are NOT yet verified against the panel.
+
+#include <Arduino.h>
+#include <SPI.h>
+
+// Pins, see docs/esp32-interface.md
+constexpr int PIN_DOT_CLK    = 18;  // VSPI SCK
+constexpr int PIN_DOT_DATA   = 23;  // VSPI MOSI
+constexpr int PIN_COL_LATCH  = 17;
+constexpr int PIN_ROW_DATA   = 16;
+constexpr int PIN_ROW_CLK    = 26;
+constexpr int PIN_ENABLE     = 22;
+constexpr int PIN_HV_WDOG    = 21;  // charge pump -> HV relay
+
+constexpr int WIDTH  = 128;
+constexpr int HEIGHT = 32;
+constexpr int ROW_BYTES = WIDTH / 8;
+
+// TODO: verify polarities on the real panel
+constexpr int ENABLE_ON  = HIGH;
+constexpr int ENABLE_OFF = !ENABLE_ON;
+
+uint8_t frame[HEIGHT][ROW_BYTES];
+
+static void makeTestPattern() {
+  for (int y = 0; y < HEIGHT; y++)
+    for (int b = 0; b < ROW_BYTES; b++)
+      frame[y][b] = ((y / 4 + b) & 1) ? 0xFF : 0x00;  // checkerboard
+}
+
+static void pulse(int pin) {
+  digitalWrite(pin, HIGH);
+  delayMicroseconds(1);
+  digitalWrite(pin, LOW);
+}
+
+static void scanFrame() {
+  for (int y = 0; y < HEIGHT; y++) {
+    SPI.writeBytes(frame[y], ROW_BYTES);
+
+    digitalWrite(PIN_ENABLE, ENABLE_OFF);        // blank while switching rows
+    pulse(PIN_COL_LATCH);
+    digitalWrite(PIN_ROW_DATA, y == 0 ? HIGH : LOW);
+    pulse(PIN_ROW_CLK);
+    digitalWrite(PIN_ENABLE, ENABLE_ON);
+
+    delayMicroseconds(200);                      // row on-time, ~120 Hz frame rate incl. overhead
+
+    // Toggle per row (~2 kHz) to keep the charge pump charged. If scanning stops, HV drops.
+    digitalWrite(PIN_HV_WDOG, !digitalRead(PIN_HV_WDOG));
+  }
+  digitalWrite(PIN_ENABLE, ENABLE_OFF);
+}
+
+void setup() {
+  // Safe state first: display disabled, watchdog idle (HV stays off).
+  pinMode(PIN_ENABLE, OUTPUT);
+  digitalWrite(PIN_ENABLE, ENABLE_OFF);
+  pinMode(PIN_HV_WDOG, OUTPUT);
+  digitalWrite(PIN_HV_WDOG, LOW);
+  pinMode(PIN_COL_LATCH, OUTPUT);
+  pinMode(PIN_ROW_DATA, OUTPUT);
+  pinMode(PIN_ROW_CLK, OUTPUT);
+
+  Serial.begin(115200);
+  SPI.begin(PIN_DOT_CLK, -1, PIN_DOT_DATA, -1);
+  SPI.setFrequency(4000000);
+  SPI.setDataMode(SPI_MODE0);
+
+  makeTestPattern();
+}
+
+void loop() {
+  scanFrame();
+}