diff --git a/src/hasp/hasp_task.cpp b/src/hasp/hasp_task.cpp
index 09650380..3957d60d 100644
--- a/src/hasp/hasp_task.cpp
+++ b/src/hasp/hasp_task.cpp
@@ -15,6 +15,10 @@ For full license information read the LICENSE file in the project folder */
 #include "hasp_gui.h"
 #endif
 
+#if HASP_USE_GPIO > 0
+#include "sys/gpio/hasp_gpio.h"
+#endif
+
 #ifdef HASP_USE_STAT_COUNTER
 extern uint16_t statLoopCounter; // measures the average looptime
 #endif
@@ -24,6 +28,10 @@ void task_every_second_cb(lv_task_t* task)
 {
     haspEverySecond(); // sleep timer & statusupdate
 
+#if HASP_USE_GPIO > 0
+    gpioEverySecond();
+#endif
+
 #if HASP_MQTT_TELNET > 0
     mqttEverySecond();
 #endif
diff --git a/src/hasp_config.h b/src/hasp_config.h
index 04160d30..ad81657b 100644
--- a/src/hasp_config.h
+++ b/src/hasp_config.h
@@ -93,6 +93,7 @@ const char FP_GUI_REPEAT_TIME[] PROGMEM        = "repeat";
 const char FP_DEBUG_TELEPERIOD[] PROGMEM       = "tele";
 const char FP_DEBUG_ANSI[] PROGMEM             = "ansi";
 const char FP_GPIO_CONFIG[] PROGMEM            = "config";
+const char FP_GPIO_ADC_MAX[] PROGMEM           = "adc_max"; // per-slot ADC ceiling for ambient-light scaling
 
 const char FP_HASP_CONFIG_FILE[] PROGMEM = "/config.json";
 
diff --git a/src/hasp_gui.cpp b/src/hasp_gui.cpp
index 17eb72be..4cd54c32 100644
--- a/src/hasp_gui.cpp
+++ b/src/hasp_gui.cpp
@@ -159,6 +159,10 @@ void guiCalibrate(void)
     // }
 
     lv_obj_invalidate(lv_disp_get_layer_sys(NULL));
+
+#if HASP_USE_CONFIG > 0
+    configWrite(); // Persist calibration data so it survives reboot
+#endif
 #endif
 }
 
diff --git a/src/lang/en_US.h b/src/lang/en_US.h
index 0ec1b257..3b49eba2 100644
--- a/src/lang/en_US.h
+++ b/src/lang/en_US.h
@@ -231,6 +231,7 @@
 #define D_GPIO_LIGHT_RELAY "Light Relay"
 #define D_GPIO_PWM "PWM"
 #define D_GPIO_DAC "DAC"
+#define D_GPIO_ADC_BACKLIGHT "Ambient Light (Auto Backlight)"
 #define D_GPIO_SERIAL_DIMMER "Serial Dimmer"
 #define D_GPIO_UNKNOWN "Unknown"
 #define D_GPIO_PIN "Pin"
diff --git a/src/main.cpp b/src/main.cpp
index b21d9e24..2555ee7f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -17,6 +17,10 @@
 #include "sys/net/hasp_time.h"
 #include "dev/device.h"
 
+#if HASP_USE_GPIO > 0
+#include "sys/gpio/hasp_gpio.h"
+#endif
+
 #if HASP_USE_CONFIG > 0
 #include "hasp_debug.h"
 #include "hasp_macro.h"
@@ -215,6 +219,10 @@ IRAM_ATTR void loop()
         /* Runs Every Second */
         haspEverySecond(); // sleep timer & statusupdate
 
+#if HASP_USE_GPIO > 0
+        gpioEverySecond();
+#endif
+
 #if HASP_USE_MQTT > 0
         mqttEverySecond();
 #endif
diff --git a/src/sys/gpio/hasp_gpio.cpp b/src/sys/gpio/hasp_gpio.cpp
index 48bfc496..70886ec9 100644
--- a/src/sys/gpio/hasp_gpio.cpp
+++ b/src/sys/gpio/hasp_gpio.cpp
@@ -329,6 +329,17 @@ static void gpio_setup_pin(uint8_t index)
             break;
         }
 
+        case hasp_gpio_type_t::HASP_ADC:
+            pinMode(gpio->pin, INPUT);
+            gpio->max = 4095; // 12-bit ADC full range (overrides the default 255 set above)
+#if defined(ARDUINO_ARCH_ESP32)
+            analogSetPinAttenuation(gpio->pin, ADC_11db); // full 0-3.3V range
+            gpio->val = analogRead(gpio->pin); // seed the smoothing filter
+#else
+            gpio->val = analogRead(gpio->pin);
+#endif
+            break;
+
         case hasp_gpio_type_t::FREE:
             return;
 
@@ -391,6 +402,33 @@ static inline bool gpio_is_output(hasp_gpio_config_t* gpio)
     return (gpio->type > hasp_gpio_type_t::USED) && (gpio->type < 0x80);
 }
 
+void gpioEverySecond(void)
+{
+#if defined(ARDUINO_ARCH_ESP32)
+    for(uint8_t i = 0; i < HASP_NUM_GPIO_CONFIG; i++) {
+        if(!gpioConfigInUse(i) || gpioConfig[i].type != hasp_gpio_type_t::HASP_ADC) continue;
+
+        // Exponential moving average (alpha = 1/8) to smooth noisy ADC readings
+        uint16_t raw      = analogRead(gpioConfig[i].pin);
+        gpioConfig[i].val = (gpioConfig[i].val * 7 + raw) >> 3;
+
+        // Only adjust backlight when the screen is currently on
+        if(!haspDevice.get_backlight_power()) continue;
+
+        // Map smoothed ADC value (0..ceiling) to backlight level (0-255).
+        // 'max' defaults to 4095 (full 12-bit range) but can be reduced for
+        // in-case installs where the sensor never sees full daylight, so the
+        // full backlight range is still exercised.
+        uint16_t ceiling = gpioConfig[i].max > 0 ? gpioConfig[i].max : 4095;
+        uint8_t level    = (uint8_t)min((uint32_t)255, (uint32_t)gpioConfig[i].val * 255 / ceiling);
+        if(gpioConfig[i].inverted) level = 255 - level;
+        if(level < 10) level = 10; // always keep screen readable in darkness
+
+        haspDevice.set_backlight_level(level);
+    }
+#endif
+}
+
 void gpioEvery5Seconds(void)
 {
     for(uint8_t i = 0; i < HASP_NUM_GPIO_CONFIG; i++) {
@@ -1001,6 +1039,40 @@ bool gpioGetConfig(const JsonObject& settings)
         changed = true;
     }
 
+    /* Save per-slot ADC ceiling values (for ambient-light auto-backlight calibration).
+     * Only written for slots with a non-default max (i.e. user has calibrated for their install).
+     * A value of 0 in the array means "use type default" (4095 for ADC). */
+    bool hasAdcMax = false;
+    for(uint8_t j = 0; j < HASP_NUM_GPIO_CONFIG; j++) {
+        if(gpioConfig[j].type == hasp_gpio_type_t::HASP_ADC && gpioConfig[j].max != 4095 && gpioConfig[j].max != 0) {
+            hasAdcMax = true;
+            break;
+        }
+    }
+    if(hasAdcMax) {
+        /* Compare against what's already in JSON before marking changed */
+        JsonArray existingAdcArr = settings[FPSTR(FP_GPIO_ADC_MAX)].as<JsonArray>();
+        uint8_t k = 0;
+        for(JsonVariant v : existingAdcArr) {
+            if(k < HASP_NUM_GPIO_CONFIG) {
+                uint16_t m = (gpioConfig[k].type == hasp_gpio_type_t::HASP_ADC) ? gpioConfig[k].max : 0;
+                if(v.as<uint16_t>() != m) changed = true;
+            } else {
+                changed = true;
+            }
+            k++;
+        }
+        if(k != HASP_NUM_GPIO_CONFIG) changed = true;
+
+        if(changed) { /* Rebuild only when necessary */
+            JsonArray adcArr = settings[FPSTR(FP_GPIO_ADC_MAX)].to<JsonArray>();
+            for(uint8_t j = 0; j < HASP_NUM_GPIO_CONFIG; j++) {
+                uint16_t m = (gpioConfig[j].type == hasp_gpio_type_t::HASP_ADC) ? gpioConfig[j].max : 0;
+                adcArr.add(m);
+            }
+        }
+    }
+
     if(changed) configOutput(settings, TAG_GPIO);
     return changed;
 }
@@ -1042,6 +1114,22 @@ bool gpioSetConfig(const JsonObject& settings)
         changed |= status;
     }
 
+    /* Load per-slot ADC ceiling values. These are applied before gpioSetup() calls
+     * gpio_setup_pin(), which preserves any non-zero max already set here. */
+    if(!settings[FPSTR(FP_GPIO_ADC_MAX)].isNull()) {
+        int j = 0;
+        JsonArray adcArr = settings[FPSTR(FP_GPIO_ADC_MAX)].as<JsonArray>();
+        for(JsonVariant v : adcArr) {
+            if(j < HASP_NUM_GPIO_CONFIG) {
+                uint16_t m = v.as<uint16_t>();
+                if(m > 0 && gpioConfig[j].type == hasp_gpio_type_t::HASP_ADC) {
+                    gpioConfig[j].max = m;
+                }
+            }
+            j++;
+        }
+    }
+
     return changed;
 }
 #endif // HASP_USE_CONFIG
diff --git a/src/sys/gpio/hasp_gpio.h b/src/sys/gpio/hasp_gpio.h
index 559bc762..d81ba5e4 100644
--- a/src/sys/gpio/hasp_gpio.h
+++ b/src/sys/gpio/hasp_gpio.h
@@ -35,6 +35,7 @@ extern "C" {
 
 void gpioSetup(void);
 IRAM_ATTR void gpioLoop(void);
+void gpioEverySecond(void);
 void gpioEvery5Seconds(void);
 
 void gpio_set_normalized_group_values(hasp_update_value_t& value);
diff --git a/src/sys/svc/hasp_http.cpp b/src/sys/svc/hasp_http.cpp
index 9a64f47a..02ff9e4e 100644
--- a/src/sys/svc/hasp_http.cpp
+++ b/src/sys/svc/hasp_http.cpp
@@ -1769,10 +1769,12 @@ static void webHandleGpioConfig()
             uint8_t pinfunc = webServer.arg("func").toInt();
             bool inverted   = webServer.arg("state").toInt();
             gpioSavePinConfig(id, pin, type, group, pinfunc, inverted);
+            configWrite(); // persist to config.json
         }
 
         if(webServer.hasArg("del")) {
             gpioSavePinConfig(id, pin, hasp_gpio_type_t::FREE, 0, 0, false);
+            configWrite(); // persist to config.json
         }
     }
 
@@ -1861,6 +1863,9 @@ static void webHandleGpioConfig()
                         case hasp_gpio_type_t::TOUCH:
                             httpMessage += D_GPIO_TOUCH;
                             break;
+                        case hasp_gpio_type_t::HASP_ADC:
+                            httpMessage += D_GPIO_ADC_BACKLIGHT;
+                            break;
                         case hasp_gpio_type_t::LED:
                             httpMessage += D_GPIO_LED;
                             break;
@@ -2068,6 +2073,7 @@ static void webHandleGpioInput()
         httpMessage += getOption(hasp_gpio_type_t::SMOKE, "Smoke", conf.type);
         httpMessage += getOption(hasp_gpio_type_t::VIBRATION, "Vibration", conf.type);
         httpMessage += getOption(hasp_gpio_type_t::WINDOW, "Window", conf.type);
+        httpMessage += getOption(hasp_gpio_type_t::HASP_ADC, D_GPIO_ADC_BACKLIGHT, conf.type);
         httpMessage += F("</select></p>");
 
         httpMessage += F("<p><b>" D_GPIO_GROUP "</b> <select id='group' name='group'>");
@@ -2082,8 +2088,8 @@ static void webHandleGpioInput()
         httpMessage += F("</select></p>");
 
         httpMessage += F("<p><b>Default State</b> <select id='state' name='state'>");
-        httpMessage += getOption(0, "Normally Open", conf.inverted);
-        httpMessage += getOption(1, "Normally Closed", conf.inverted);
+        httpMessage += getOption(0, D_GPIO_STATE_NORMAL, conf.inverted);
+        httpMessage += getOption(1, D_GPIO_STATE_INVERTED, conf.inverted);
         httpMessage += F("</select></p>");
 
         httpMessage += F("<p><b>Resistor</b> <select id='func' name='func'>");
diff --git a/src/sys/svc/hasp_http_async.cpp b/src/sys/svc/hasp_http_async.cpp
index 45c4e0f6..4edda146 100644
--- a/src/sys/svc/hasp_http_async.cpp
+++ b/src/sys/svc/hasp_http_async.cpp
@@ -1534,6 +1534,9 @@ void webHandleGpioConfig(AsyncWebServerRequest* request)
                         case hasp_gpio_type_t::TOUCH:
                             httpMessage += F(D_GPIO_TOUCH);
                             break;
+                        case hasp_gpio_type_t::HASP_ADC:
+                            httpMessage += F(D_GPIO_ADC_BACKLIGHT);
+                            break;
                         case hasp_gpio_type_t::LED:
                             httpMessage += F(D_GPIO_LED);
                             break;
@@ -1808,6 +1811,9 @@ void webHandleGpioInput(AsyncWebServerRequest* request)
         selected = (conf.type == hasp_gpio_type_t::WINDOW);
         httpMessage += getOption(hasp_gpio_type_t::WINDOW, F("Window"), selected);
 
+        selected = (conf.type == hasp_gpio_type_t::HASP_ADC);
+        httpMessage += getOption(hasp_gpio_type_t::HASP_ADC, F(D_GPIO_ADC_BACKLIGHT), selected);
+
         httpMessage += F("</select></p>");
 
         httpMessage += F("<p><b>" D_GPIO_GROUP "</b> <select id='group' name='group'>");
diff --git a/user_setups/esp32/esp32-2432s024.ini b/user_setups/esp32/esp32-2432s024.ini
index 0e737480..0578f4c9 100644
--- a/user_setups/esp32/esp32-2432s024.ini
+++ b/user_setups/esp32/esp32-2432s024.ini
@@ -38,6 +38,29 @@ build_flags =
     -D LED_BLUE=16
 ;endregion
 
+;region -- Ambient light sensor (GT36516) ----------------
+; Light-dependent resistor on IO34.
+; IO34 is input-only on ESP32 (ADC1 channel 6, no internal pull resistors).
+;
+; PCB HARDWARE BUG: The published schematic shows a 1M/1M voltage divider
+; (1MΩ to 3.3V, 1MΩ to GND) with the LDR between the divider mid-point and IO34.
+; In practice the LDR measures 470Ω (bright) to 4kΩ (dark), which with a 1MΩ
+; pull-up produces only 1–13mV at IO34 — well below the ESP32 ADC floor (~150mV).
+; analogRead() returns 0 across all light conditions with the stock resistor.
+;
+; REQUIRED HARDWARE FIX: Replace the 1MΩ pull-up resistor (3.3V side) with 1.5kΩ.
+; 1.5kΩ is the geometric mean of the LDR's resistance range (√(470×4000) ≈ 1.4kΩ)
+; and centres the dynamic range across the full ADC scale:
+;   Bright (470Ω LDR)  : ~0.79V → ADC ≈  981
+;   Desk   (1.2kΩ LDR) : ~1.47V → ADC ≈ 1825
+;   Dark   (4kΩ LDR)   : ~2.40V → ADC ≈ 2979
+; The 1MΩ resistor to GND can be left in place; it has negligible effect.
+;
+; Configure via web UI: GPIO Settings → Add New Pin (Input) → IO34
+;   Type: Ambient Light (Auto Backlight)
+;   Default State: Inverted  ← required: bright light lowers voltage on this circuit
+;endregion
+
 ;region -- TFT_eSPI build options ------------------------
     ${esp32.hspi}        ; Use HSPI hardware SPI bus
     ;-D USER_SETUP_LOADED=1