Move the Nano link to Serial2, update READMEs

- ESP32 talks to the Nano on UART2 (GPIO 17 TX / GPIO 16 RX); Serial (USB)
  is now free for debug output and boot messages no longer reach the Nano
- README: wiring table, actual schedule (clock from 08:00), TODO section
  for the rewiring

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

src/esp32/README.md

@@ -3,8 +3,9 @@
 PlatformIO environments: `esp32` (OTA) and `esp32_usb` (USB)
 
 The ESP32 decides what is shown on the display. It never touches the panel itself. The
-BROSE9323 driver is built with `-D ESPSERIAL`, so every GFX call is sent over `Serial`
-(115200 baud) to the Nano.
+BROSE9323 driver is built with `-D ESPSERIAL`, so every GFX call is sent to the Nano over
+`Serial2` (UART2, GPIO 17 TX / GPIO 16 RX, 115200 baud). `Serial` (USB) is only used for
+debug output. Wiring is described in the [main README](../../README.md#wiring-between-esp32-and-nano).
 
 ## Files
 
@@ -40,10 +41,10 @@ BROSE9323 driver is built with `-D ESPSERIAL`, so every GFX call is sent over `S
 
 | Time | Display |
 |------|---------|
-| 07:00 – 17:00 | Pikachu and the clock, updated every minute |
+| 08:00 – 17:00 | Pikachu and the clock, updated every minute |
 | 17:00 – 22:00 | Yawning Pikachu and the clock |
-| 22:00 – 23:30 | Clock drawn only on the quarter hour; power is off in between |
-| night | Screen cleared, power off |
+| 22:00 – 23:30 | Clock shown only during the minutes :00, :15, :30 and :45; power is off in between |
+| 23:31 – 08:00 | Screen cleared, power off |
 
 ## Adding bitmaps
 

src/esp32/libs.h

@@ -45,7 +45,10 @@ bool power = true;
 
 const int led1 = BUILTIN_LED; // Pin of the LED
 const int relay = 13; // Pin of the relay, powers the panels and the Nano (LOW = on)
-const int nano_tx = 1; // UART0 TX, wired to the Nano RX
+// Link to the Nano on UART2. Serial (UART0) stays free for USB / debug output.
+HardwareSerial &nanoSerial = Serial2;
+const int nano_rx = 16; // UART2 RX, wired to the Nano TX (through a 5V -> 3.3V divider)
+const int nano_tx = 17; // UART2 TX, wired to the Nano RX
 bool relay_on = false;
 // Max wait for the Nano's READY after power on (also the wait when Nano TX is not wired to our RX)
 const uint32_t NANO_BOOT_TIMEOUT = 3000;

src/esp32/main.cpp

@@ -14,9 +14,9 @@ void waitForNano()
   uint32_t start = millis();
   while (millis() - start < NANO_BOOT_TIMEOUT)
   {
-    while (Serial.available())
+    while (nanoSerial.available())
     {
-      char c = Serial.read();
+      char c = nanoSerial.read();
       if (c == '\n')
       {
         line[len] = '\0';
@@ -39,10 +39,10 @@ void relayOn()
   if (relay_on)
     return;
 
-  Serial.begin(115200);
+  nanoSerial.begin(115200, SERIAL_8N1, nano_rx, nano_tx);
   // drop old data (e.g. ERR replies) so only a new READY counts
-  while (Serial.available())
-    Serial.read();
+  while (nanoSerial.available())
+    nanoSerial.read();
 
   digitalWrite(relay, LOW);
   waitForNano();
@@ -55,8 +55,8 @@ void relayOff()
   relay_on = false;
 
   // An idle UART TX line is high and would power the Nano through its RX pin
-  Serial.flush();
-  Serial.end();
+  nanoSerial.flush();
+  nanoSerial.end();
   pinMode(nano_tx, INPUT);
 }
 void turnPowerOff(uint32_t delay = 30000, bool _turn_hassio_power_off = false)
@@ -289,7 +289,7 @@ void setup()
   pinMode(relay, OUTPUT);
   relayOn();
 
-  display.begin(&Serial);
+  display.begin(&nanoSerial);
   // display.setTiming(200);
   // display.setTiming(180);
   // display.setTiming(220); // works best so far