Docs: WEMOS D1 R1 (ESP8266) instead of ESP32

The reference build now uses a D1 R1. The example config targets
esp8266/d1 and sends on GPIO2 (header pin D9, UART1 TX), which leaves
UART0 free for the USB logger. The README wiring and signal-level notes
are updated to match.

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

README.md

@@ -42,7 +42,7 @@ external_components:
 
 uart:
   id: uart_vfd
-  tx_pin: GPIO17
+  tx_pin: GPIO2     # D1 R1 pin D9 (UART1 TX on the ESP8266)
   baud_rate: 9600   # match the display's jumpers (factory default: 9600, no parity)
 
 time:               # required by the component (used by samsung_vfd.printf)
@@ -54,6 +54,10 @@ samsung_vfd:
   uart_id: uart_vfd
 ```
 
+The `uart:` block above uses the pin from the reference build, a WEMOS D1 R1
+(ESP8266); see [Hardware](#hardware). Any ESPHome board with a free TX pin
+works.
+
 For a complete device, copy [examples/samsung-vfd.yaml](examples/samsung-vfd.yaml)
 into your ESPHome config folder. Add the keys from
 [examples/secrets.yaml.example](examples/secrets.yaml.example) to your
@@ -65,13 +69,16 @@ The board in the photos is a 20L203DA5 (rev A). The included
 [datasheet](docs/20L203DA12-datasheet.pdf) is for the 20L203DA12, a variant
 with the same command set.
 
+The reference build drives it from a WEMOS D1 R1, an UNO-sized ESP8266 board,
+through a MAX3232. The [desk case](case/README.md) is made for that board.
+
 ### Connector (3-pin Molex 5046-03A)
 
 | Pin | Signal | Connect to |
 |-----|--------|------------|
 | 1 | VCC | 5–24 V DC supply |
-| 2 | RXD | MAX3232 T1OUT (T1IN ← ESP32 GPIO17), see below |
-| 3 | GND | supply GND, MAX3232 GND **and** ESP32 GND |
+| 2 | RXD | MAX3232 T1OUT (T1IN ← D1 R1 GPIO2), see below |
+| 3 | GND | supply GND, MAX3232 GND **and** D1 R1 GND |
 
 ### Power
 
@@ -83,21 +90,21 @@ for example 12 V at 1 A, and connect the grounds together.
 ### Signal levels
 
 The RXD input goes through an RS-232 receiver: it expects ±3 to ±15 V and
-idles at the negative level (mark). It tolerates ±30 V, so a 3.3 V ESP32 pin
+idles at the negative level (mark). It tolerates ±30 V, so a 3.3 V ESP8266 pin
 can't damage it. There are two ways to connect it:
 
 - **Through a MAX3232 (recommended, and how the original build is wired).**
-  Power the MAX3232 from the ESP32's 3.3 V, then wire GPIO17 → T1IN and
+  Power the MAX3232 from the D1's 3.3 V, then wire GPIO2 → T1IN and
   T1OUT → display RXD. The MAX3232 produces real RS-232 levels and does the
-  inversion itself, so use the plain `tx_pin: GPIO17`.
-- **Direct from the ESP32.** A plain TTL signal arrives inverted, so wire
-  GPIO17 straight to RXD and invert the pin in the UART config:
+  inversion itself, so use the plain `tx_pin: GPIO2`.
+- **Direct from the ESP8266.** A plain TTL signal arrives inverted, so wire
+  GPIO2 straight to RXD and invert the pin in the UART config:
 
   ```yaml
   uart:
     id: uart_vfd
     tx_pin:
-      number: GPIO17
+      number: GPIO2
       inverted: true
     baud_rate: 9600
   ```
@@ -109,6 +116,14 @@ can't damage it. There are two ways to connect it:
 If the display shows garbage or nothing at all, the inversion setting is the
 first thing to check: off with a MAX3232, on without one.
 
+### Why GPIO2
+
+The ESP8266 has two hardware UARTs. UART0 (GPIO1/GPIO3) is the USB serial
+port that ESPHome's logger uses. UART1 can only transmit, and only on GPIO2,
+which is all this display needs. On the D1 R1, GPIO2 is the pin labelled D9.
+GPIO2 must be high at boot; the MAX3232's input doesn't pull it low, so that
+is fine.
+
 ### Jumpers
 
 The 2×8 pin header on the board selects the following. Jumpers are read only
@@ -209,7 +224,7 @@ table, character set and user characters. It sends them again after
 | `samsung_vfd.set_blink` | `interval:` (templatable time): on for that long, off for that long, in 13 ms steps up to 3.3 s. `0ms` stops blinking. |
 | `samsung_vfd.turn_off` / `turn_on` | Blanks the screen and brings it back without losing its contents. |
 | `samsung_vfd.set_annunciator` | `column:` 1–20, or 0 for all; `state:` true/false (both templatable). Switches the triangle under that column. |
-| `samsung_vfd.reinit` | Resets the display, re-applies all settings and redraws the screen. Use it when the display was power-cycled without the ESP. |
+| `samsung_vfd.reinit` | Resets the display, re-applies all settings and redraws the screen. Use it when the display was power-cycled without the ESP8266. |
 | `samsung_vfd.self_test` | Runs the built-in self-test (about 20 s), then restores settings and the screen. |
 
 ### Raw control