diff --git a/ch32v-insert-coin/src/app.rs b/ch32v-insert-coin/src/app.rs
index da8b9ca..54a2768 100644
--- a/ch32v-insert-coin/src/app.rs
+++ b/ch32v-insert-coin/src/app.rs
@@ -11,7 +11,7 @@ pub enum State {
 
 mod settings {
 
-    #[derive(Default, Clone, Copy)]
+    #[derive(Debug, Default, Clone, Copy)]
     pub enum Level {
         Off,
         Low,
@@ -33,6 +33,19 @@ mod settings {
         }
     }
 
+    // volume control
+    impl Level {
+        pub fn as_volume_divisor(&self) -> u8 {
+            match self {
+                Self::Off => u8::MAX,
+                Self::Low => 4,
+                Self::Medium => 3,
+                Self::High => 2,
+                Self::Maximum => 1,
+            }
+        }
+    }
+
     #[derive(Clone, Copy)]
     pub struct Settings {
         pub brightness: Level,
@@ -285,8 +298,8 @@ impl App {
             self.services
                 .led0
                 .set_amplitude(self.sequences.led0.get_value());
-            #[cfg(feature = "enable_print")]
-            println!("led0 sevice {}", self.sequences.led0.get_value());
+            // #[cfg(feature = "enable_print")]
+            // println!("led0 sevice {}", self.sequences.led0.get_value());
         }
         if self.timers.led1_timer.need_service() {
             self.timers.led1_timer.service();
@@ -294,8 +307,8 @@ impl App {
             self.services
                 .led1
                 .set_amplitude(self.sequences.led1.get_value());
-            #[cfg(feature = "enable_print")]
-            println!("led1 service");
+            // #[cfg(feature = "enable_print")]
+            // println!("led1 service");
         }
         if self.timers.led2_timer.need_service() {
             self.timers.led2_timer.service();
@@ -303,8 +316,8 @@ impl App {
             self.services
                 .led2
                 .set_amplitude(self.sequences.led2.get_value());
-            #[cfg(feature = "enable_print")]
-            println!("led2 service");
+            // #[cfg(feature = "enable_print")]
+            // println!("led2 service");
         }
 
         // services
@@ -328,7 +341,7 @@ impl App {
         }
 
         if self.services.synth0.need_service() {
-            let out = self.services.synth0.service();
+            let out = self.services.synth0.service() / self.settings.volume.as_volume_divisor();
             self.interfaces
                 .pwm_core
                 .write_amplitude(ch32_hal::timer::Channel::Ch4, out);
@@ -336,11 +349,31 @@ impl App {
     }
 }
 
+// interfaces to the app (for buttons, etc.)
+impl App {
+    pub fn volume_button(&mut self) {
+        self.settings.volume.next();
+        #[cfg(feature = "enable_print")]
+        println!("new volume: {:?}", self.settings.volume);
+    }
+    pub fn brightness_button(&mut self) {
+        #[cfg(feature = "enable_print")]
+        println!("brightness button app handler");
+        // TODO
+    }
+    pub fn main_button(&mut self) {
+        // TODO
+    }
+    pub fn coin_detect(&mut self) {
+        // TODO
+    }
+}
+
 // TODO LIST
 //
 // AUDIO:
-// 1. volume control
 // 2. dac switching
+// 3. amp_en control
 //
 // LED:
 // 1. brightness control
@@ -355,3 +388,6 @@ impl App {
 // 1. deep sleep
 // 2. battery voltage monitoring
 // 3. battery voltage cutoff
+//
+// STRETCH TODO LIST
+// 1. clean up edge detector
diff --git a/ch32v-insert-coin/src/main.rs b/ch32v-insert-coin/src/main.rs
index 9ddeb15..9990634 100644
--- a/ch32v-insert-coin/src/main.rs
+++ b/ch32v-insert-coin/src/main.rs
@@ -329,6 +329,25 @@ fn app_main(mut p: hal::Peripherals) -> ! {
     app.init();
     loop {
         // system servicing
+        //
+        // edge detector
+        if !volume_btn_input.active() {
+            let volume_btn_curr = volume_btn_input.is_high_immediate();
+            if volume_btn_prev != volume_btn_curr {
+                volume_btn_input.begin();
+                volume_btn_prev = volume_btn_curr;
+            }
+        }
+
+        volume_btn_input.service();
+        if volume_btn_input.ready() {
+            #[cfg(feature = "enable_print")]
+            println!("volume btn value: {}", volume_btn_input.value());
+            if !volume_btn_input.value() {
+                app.volume_button();
+            }
+            volume_btn_input.reset();
+        }
 
         // systick tick
         if unsafe {
@@ -347,17 +366,6 @@ fn app_main(mut p: hal::Peripherals) -> ! {
         // interfaces.service();
     }
 
-    //         // edge detector
-    //         if !volume_btn_input.active() {
-    //             let volume_btn_curr = volume_btn_input.is_high_immediate();
-    //             if volume_btn_prev != volume_btn_curr {
-    //                 volume_btn_prev = volume_btn_curr;
-    //                 unsafe {
-    //                     INPUT_FLAGS.volume_btn_flag = true;
-    //                 }
-    //             }
-    //         }
-
     //         if !light_ctrl_btn_input.active() {
     //             let light_ctrl_btn_curr = light_ctrl_btn_input.is_high_immediate();
     //             if light_ctrl_btn_prev != light_ctrl_btn_curr {