diff --git a/common/keyboard.c b/common/keyboard.c
index 9a809ff4..dde91a29 100644
--- a/common/keyboard.c
+++ b/common/keyboard.c
@@ -15,6 +15,8 @@ You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 #include <stdint.h>
+#include <util/delay.h>
+#include <avr/wdt.h>
 #include "keyboard.h"
 #include "matrix.h"
 #include "keymap.h"
@@ -30,12 +32,14 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "bootmagic.h"
 #include "eeconfig.h"
 #include "backlight.h"
+#include "suspend.h"
 #ifdef MOUSEKEY_ENABLE
 #   include "mousekey.h"
 #endif
 #ifdef PS2_MOUSE_ENABLE
 #   include "ps2_mouse.h"
 #endif
+#include "lufa.h"
 
 
 #ifdef MATRIX_HAS_GHOST
@@ -83,7 +87,25 @@ void keyboard_task(void)
     static uint8_t led_status = 0;
     matrix_row_t matrix_row = 0;
     matrix_row_t matrix_change = 0;
+    static uint32_t last_key_time = 0;
 
+/*
+#define SLEEP_TIME_MS 10000
+    // (USB_DeviceState == DEVICE_STATE_Suspended) {
+    //if (timer_elapsed32(last_key_time) > SLEEP_TIME_MS) {
+    // TODO: remove LUFA dependent code
+    if (!USB_IsInitialized && timer_elapsed32(last_key_time) > SLEEP_TIME_MS) {
+        matrix_power_down();
+        // TODO: power down only when no USB connection
+        // Or it makes USB connection lost or suspended
+        suspend_power_down(WDTO_15MS);
+        matrix_power_up();
+    }
+    else {
+        matrix_power_down();
+        matrix_power_up();
+    }
+*/
     matrix_scan();
     for (uint8_t r = 0; r < MATRIX_ROWS; r++) {
         matrix_row = matrix_get_row(r);
@@ -105,6 +127,7 @@ void keyboard_task(void)
                     });
                     // record a processed key
                     matrix_prev[r] ^= ((matrix_row_t)1<<c);
+                    last_key_time = timer_read32();
                     // process a key per task call
                     goto MATRIX_LOOP_END;
                 }
diff --git a/common/keyboard.h b/common/keyboard.h
index 60f8a89d..6442716f 100644
--- a/common/keyboard.h
+++ b/common/keyboard.h
@@ -62,6 +62,9 @@ void keyboard_init(void);
 void keyboard_task(void);
 void keyboard_set_leds(uint8_t leds);
 
+__attribute__ ((weak)) void matrix_power_up(void) {}
+__attribute__ ((weak)) void matrix_power_down(void) {}
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/common/matrix.h b/common/matrix.h
index d1d14a6e..23fef78f 100644
--- a/common/matrix.h
+++ b/common/matrix.h
@@ -53,4 +53,9 @@ matrix_row_t  matrix_get_row(uint8_t row);
 void matrix_print(void);
 
 
+/* power control */
+void matrix_power_up(void);
+void matrix_power_down(void);
+
+
 #endif
diff --git a/keyboard/hhkb_rn42/hhkb_avr.h b/keyboard/hhkb_rn42/hhkb_avr.h
index 313effed..f007d766 100644
--- a/keyboard/hhkb_rn42/hhkb_avr.h
+++ b/keyboard/hhkb_rn42/hhkb_avr.h
@@ -43,11 +43,10 @@ static inline void KEY_PREV_ON(void) { (PORTB |=  (1<<7)); }
 static inline void KEY_PREV_OFF(void) { (PORTB &= ~(1<<7)); }
 #ifdef HHKB_POWER_SAVING
 static inline void KEY_POWER_ON(void) {
-    _delay_ms(10);                      // TODO: sleep to save power
     DDRB = 0xFF; PORTB = 0x40;          // change pins output
     DDRD |= (1<<4); PORTD |= (1<<4);    // MOS FET switch on
     /* Without this wait you will miss or get false key events. */
-    _delay_ms(1);                       // wait for powering up
+    _delay_ms(5);                       // wait for powering up
 }
 static inline void KEY_POWER_OFF(void) {
     /* input with pull-up consumes less than without it when pin is open. */
@@ -74,7 +73,7 @@ static inline void KEY_INIT(void)
     KEY_UNABLE();
     KEY_PREV_OFF();
 
-    KEY_POWER_OFF();
+    KEY_POWER_ON();
 }
 static inline void KEY_SELECT(uint8_t ROW, uint8_t COL)
 {
diff --git a/keyboard/hhkb_rn42/matrix.c b/keyboard/hhkb_rn42/matrix.c
index b0af4baa..c6c444ff 100644
--- a/keyboard/hhkb_rn42/matrix.c
+++ b/keyboard/hhkb_rn42/matrix.c
@@ -27,8 +27,16 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "timer.h"
 #include "matrix.h"
 #include "hhkb_avr.h"
+#include <avr/wdt.h>
+#include "suspend.h"
+#include "lufa.h"
 
 
+// matrix power saving
+#define MATRIX_POWER_SAVE       10000
+static uint32_t matrix_last_modified = 0;
+static bool matrix_power = true;
+
 // matrix state buffer(1:on, 0:off)
 static matrix_row_t *matrix;
 static matrix_row_t *matrix_prev;
@@ -72,7 +80,7 @@ uint8_t matrix_scan(void)
     matrix_prev = matrix;
     matrix = tmp;
 
-    KEY_POWER_ON();
+    matrix_power_up();
     for (uint8_t row = 0; row < MATRIX_ROWS; row++) {
         for (uint8_t col = 0; col < MATRIX_COLS; col++) {
             KEY_SELECT(row, col);
@@ -126,8 +134,9 @@ uint8_t matrix_scan(void)
             // This takes 25us or more to make sure KEY_STATE returns to idle state.
             _delay_us(75);
         }
+        if (matrix[row] ^ matrix_prev[row]) matrix_last_modified = timer_read32();
     }
-    KEY_POWER_OFF();
+    matrix_power_down();
     return 1;
 }
 
@@ -165,3 +174,18 @@ void matrix_print(void)
         xprintf("%02X: %08b\n", row, bitrev(matrix_get_row(row)));
     }
 }
+
+void matrix_power_up(void) {
+    if (matrix_power) return;
+    KEY_POWER_ON();
+    matrix_power = true;
+}
+void matrix_power_down(void) {
+    if (!matrix_power) return;
+    // doesn't power save while USB connection is active
+    if (USB_DeviceState == DEVICE_STATE_Configured) return;
+    if (timer_elapsed32(matrix_last_modified) <= MATRIX_POWER_SAVE) return;
+    KEY_POWER_OFF();
+    suspend_power_down(WDTO_15MS);
+    matrix_power = false;
+}
diff --git a/keyboard/hhkb_rn42/rn42/main.c b/keyboard/hhkb_rn42/rn42/main.c
index a3a37c07..43d88706 100644
--- a/keyboard/hhkb_rn42/rn42/main.c
+++ b/keyboard/hhkb_rn42/rn42/main.c
@@ -85,7 +85,7 @@ int main(void)
     print("Keyboard start.\n");
     while (1) {
         while (USB_DeviceState == DEVICE_STATE_Suspended) {
-            suspend_power_down();
+            suspend_power_down(WDTO_120MS);
             if (USB_Device_RemoteWakeupEnabled && suspend_wakeup_condition()) {
                     USB_Device_SendRemoteWakeup();
             }