diff --git a/main/index.html b/main/index.html
index de74eb2..3628eae 100644
--- a/main/index.html
+++ b/main/index.html
@@ -263,7 +263,7 @@
 
                 <div class="control-group">
                     <label>Rate(Hz)</label>
-                    <input type="number" id="sampleRate" value="10000" min="1" max="83333">
+                    <input type="number" id="sampleRate" value="20000" min="20000" max="2000000">
                 </div>
 
                 <div class="control-group" style="display: none;">
@@ -279,10 +279,10 @@
                 <div class="control-group">
                     <label>Atten</label>
                     <select id="atten">
-                        <option value="0">0dB</option>
-                        <option value="1">2.5dB</option>
-                        <option value="2">6dB</option>
-                        <option value="3" selected>11dB</option>
+                        <option value="0">0dB (0–1.0V)</option>
+                        <option value="1">2.5dB (0–1.34V)</option>
+                        <option value="2">6dB (0–2.0V)</option>
+                        <option value="3" selected>11dB (0–3.6V)</option>
                     </select>
                 </div>
 
diff --git a/main/main.c b/main/main.c
index 0ad1fe2..86ce728 100644
--- a/main/main.c
+++ b/main/main.c
@@ -40,8 +40,11 @@ static void start_webserver(void);
 #define ADC_ATTEN ADC_ATTEN_DB_11
 #define ADC_BIT_WIDTH ADC_BITWIDTH_12
 
-#define ADC_OUTPUT_TYPE ADC_DIGI_OUTPUT_FORMAT_TYPE2
-#define ADC_GET_DATA(p_data) ((p_data)->type2.data)
+// TYPE2 is only available on newer chips (S3, C6, etc.). ESP32 (WROOM-32) requires TYPE1.
+// #define ADC_OUTPUT_TYPE ADC_DIGI_OUTPUT_FORMAT_TYPE2
+// #define ADC_GET_DATA(p_data) ((p_data)->type2.data)
+#define ADC_OUTPUT_TYPE ADC_DIGI_OUTPUT_FORMAT_TYPE1
+#define ADC_GET_DATA(p_data) ((p_data)->type1.data)
 
 /*
  * Web Server Configuration
@@ -421,9 +424,15 @@ static esp_err_t params_handler(httpd_req_t* req) {
   cJSON* root = cJSON_Parse(buf);
   if (root) {
     cJSON* sample_rate = cJSON_GetObjectItem(root, "sample_rate");
-    if (sample_rate && s_sample_rate != sample_rate->valueint) {
-      s_reconfig_needed = true;
-      s_sample_rate = sample_rate->valueint;
+    if (sample_rate) {
+      uint32_t requested = (uint32_t)sample_rate->valueint;
+      // ESP32 ADC continuous mode valid range: 20kHz – 2MHz (SOC_ADC_SAMPLE_FREQ_THRES_LOW/HIGH)
+      if (requested < 20000) requested = 20000;
+      if (requested > 2000000) requested = 2000000;
+      if (s_sample_rate != requested) {
+        s_reconfig_needed = true;
+        s_sample_rate = requested;
+      }
     }
     cJSON* atten = cJSON_GetObjectItem(root, "atten");
     if (atten && s_atten != (adc_atten_t)atten->valueint) {