diff --git a/resources/led-bridge/firmware/led-indicator.ino b/resources/led-bridge/firmware/led-indicator.ino
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+++ b/resources/led-bridge/firmware/led-indicator.ino
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+// led-indicator.ino — reference firmware for the led-bridge LED indicator.
+//
+// This sketch runs on an ESP32 driving an 80-pixel Adafruit NeoPixel strip.
+// It is NOT built, flashed, or otherwise used by this repo at runtime — it
+// lives here purely for reference alongside ../led-bridge.go, the host-side
+// Viam module that drives it over USB serial.
+//
+// Hardware / wiring:
+//   - NeoPixel data pin: GPIO 18
+//   - Strip length:      80 pixels
+//   - Serial baud:       115200  (must match led-bridge.go's defaultBaudRate)
+//
+// Serial protocol: led-bridge.go writes one '\n'-terminated line per update,
+// each a JSON object of the form {"state":"<mode>"} (see actionForState in
+// led-bridge.go). This sketch does a substring match on that line, so the
+// JSON wrapper is matched transparently — it only cares that one of these
+// keywords appears:
+//   - "idle"        -> LEDs off
+//   - "listening"   -> solid blue
+//   - "thinking"    -> orange sine pulse (~800ms period)
+//   - "responding"  -> solid orange
+// Any line without a recognized keyword is logged and ignored.
+
+#include <Adafruit_NeoPixel.h>
+
+const int  LED_PIN    = 18;
+const int  NUM_PIXELS = 80;
+const long BAUD_RATE  = 115200;
+const uint8_t BRIGHTNESS = 80;
+
+Adafruit_NeoPixel strip(NUM_PIXELS, LED_PIN, NEO_GRB + NEO_KHZ800);
+
+enum Mode { MODE_IDLE, MODE_LISTENING, MODE_THINKING, MODE_RESPONDING };
+Mode currentMode = MODE_IDLE;
+String inputBuffer;
+
+void setup() {
+  Serial.begin(BAUD_RATE);
+  strip.begin();
+  strip.setBrightness(BRIGHTNESS);
+
+  // Boot self-test: R G B on first 3 LEDs for 2 seconds.
+  strip.setPixelColor(0, strip.Color(255, 0, 0));
+  strip.setPixelColor(1, strip.Color(0, 255, 0));
+  strip.setPixelColor(2, strip.Color(0, 0, 255));
+  strip.show();
+  delay(2000);
+  strip.clear();
+  strip.show();
+
+  Serial.println("ready");
+}
+
+void loop() {
+  readSerial();
+  render();
+  delay(20);
+}
+
+void readSerial() {
+  while (Serial.available()) {
+    char c = Serial.read();
+    if (c == '\n') {
+      handleLine(inputBuffer);
+      inputBuffer = "";
+    } else if (c != '\r') {
+      inputBuffer += c;
+    }
+  }
+}
+
+void handleLine(const String &line) {
+  Serial.print("received line: ");
+  Serial.println(line);
+  if (line.indexOf("listening") >= 0) {
+    currentMode = MODE_LISTENING;
+    Serial.println("-> mode: listening");
+  } else if (line.indexOf("thinking") >= 0) {
+    currentMode = MODE_THINKING;
+    Serial.println("-> mode: thinking");
+  } else if (line.indexOf("idle") >= 0) {
+    currentMode = MODE_IDLE;
+    Serial.println("-> mode: idle");
+  } else if (line.indexOf("responding") >= 0) {
+    currentMode = MODE_RESPONDING;
+    Serial.println("-> mode: responding");
+  } else {
+    Serial.println("-> unrecognized, ignoring");
+  }
+}
+
+// Render a single-color sine pulse across the whole strip.
+// period_ms controls speed (smaller = faster). r, g, b set the hue.
+void pulseColor(uint16_t period_ms, uint8_t r, uint8_t g, uint8_t b) {
+  float phase = (millis() % period_ms) / (float)period_ms;
+  float wave = (sin(phase * 2.0f * PI) + 1.0f) * 0.5f;
+  float scale_lo = 10.0f / 255.0f;
+  float scale = scale_lo + wave * (1.0f - scale_lo);
+  uint32_t color = strip.Color(
+    (uint8_t)(r * scale),
+    (uint8_t)(g * scale),
+    (uint8_t)(b * scale));
+  for (int i = 0; i < NUM_PIXELS; i++) {
+    strip.setPixelColor(i, color);
+  }
+  strip.show();
+}
+
+void solidColor(uint8_t r, uint8_t g, uint8_t b) {
+  uint32_t color = strip.Color(r, g, b);
+  for (int i = 0; i < NUM_PIXELS; i++) {
+    strip.setPixelColor(i, color);
+  }
+  strip.show();
+}
+
+void render() {
+  switch (currentMode) {
+    case MODE_IDLE:
+      strip.clear();
+      strip.show();
+      break;
+    case MODE_LISTENING:
+      solidColor(0, 0, 255);
+      break;
+    case MODE_THINKING:
+      pulseColor(800, 255, 140, 0);
+      break;
+    case MODE_RESPONDING:
+      solidColor(255, 140, 0);
+      break;
+  }
+}