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>

README.md

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+# Plasma DMD
+
+Drive a second-hand 128×32 pinball **plasma** dot-matrix display (originally on a Williams WPC
+DMD controller) standalone, from a **Wemos D1 mini ESP32**, powered from a single **12 V DC** brick.
+
+The display power supply is built from cheap modules plus a copy of the regulator section of the
+Stern/Sega display PSU (520-5138-00). The original transformer and AC front end are not used.
+
+> ⚠️ **High voltage.** The panel runs on about +65 V, −100 V and −112 V, which is about 175 V
+> between rails. That can injure you. Read [docs/safety.md](docs/safety.md) before powering anything.
+
+## The panel
+
+- Bought second-hand on 18 September 2021 for €37.
+- Originally driven by a Williams WPC DMD controller board. No original controller or PSU came with it.
+
+## Layout
+
+| Path | Contents |
+|---|---|
+| [docs/power-supply.md](docs/power-supply.md) | PSU design: block diagram, analysis of the original board, changes |
+| [hardware/psu-schematic.svg](hardware/psu-schematic.svg) | PSU schematic (generated by [hardware/psu_schematic.py](hardware/psu_schematic.py)) |
+| [hardware/kicad/](hardware/kicad/) | KiCad 10 project for the PSU carrier board (schematic + net classes, PCB not started) |
+| [docs/safety.md](docs/safety.md) | Safety design (HV watchdog, fusing, layout, bring-up procedure) |
+| [docs/esp32-interface.md](docs/esp32-interface.md) | ESP32 pin plan, 74HCT245 level shifter, panel signals |
+| [docs/bom.md](docs/bom.md) | Bill of materials |
+| [reference/](reference/) | Original Stern 520-5138-00 display PSU schematic |
+| [firmware/](firmware/) | PlatformIO project for the ESP32 |
+
+## Status
+
+- [ ] Identify panel: manufacturer/part number from its label
+- [ ] Map the panel's power connector pins (WPC panel ≠ Stern CN2 pinout) and check if +12 V is used
+- [ ] Map the panel's 14-pin data connector
+- [ ] Lay out the PSU PCB in KiCad ([hardware/kicad/](hardware/kicad/README.md))
+- [ ] Order parts ([docs/bom.md](docs/bom.md))
+- [ ] Build and bench-test the PSU **without the panel** ([bring-up](docs/safety.md#bring-up-procedure))
+- [ ] Build HV watchdog and verify that the relay drops when toggling stops
+- [ ] Firmware: row scanning with test pattern
+- [ ] First power-up with panel (series resistors, current measurement)
+- [ ] Firmware: greyscale, content source (Wi-Fi / serial)