diff --git a/main.py b/main.py
index 7a7db8e..8646cd3 100644
--- a/main.py
+++ b/main.py
@@ -32,8 +32,10 @@ DIN_PINS = (25, 26, 27, 32)
 DOUT_PINS = (18, 19)
 
 digital_inputs = [Pin(pin, Pin.IN, Pin.PULL_UP) for pin in DIN_PINS]
-digital_outputs = [Pin(pin, Pin.OUT, value=0) for pin in DOUT_PINS]
-
+# Low-level trigger relay:
+# GPIO HIGH = relay OFF
+# GPIO LOW  = relay ON
+digital_outputs = [Pin(pin, Pin.OUT, value=1) for pin in DOUT_PINS]
 
 # ---------------- SERIAL CONFIG ----------------
 
@@ -102,15 +104,18 @@ poller.register(sys.stdin, select.POLLIN)
 # ============================================================
 # DOUT / gripper
 # ============================================================
-
 def clear_douts():
     global dout_shadow
 
+    # Logical DOUT state reported to PC.
+    # 0 means no gripper command active.
     dout_shadow = 0
 
+    # Low-level trigger relay:
+    # HIGH = relay OFF
+    # LOW  = relay ON
     for pin in digital_outputs:
-        pin.value(0)
-
+        pin.value(1)
 
 def set_gripper(mode):
     global dout_shadow
@@ -120,39 +125,47 @@ def set_gripper(mode):
     #   1 = OPEN
     #   2 = CLOSE
     #
-    # DOUT[0] = GPIO18
-    # DOUT[1] = GPIO19
+    # DOUT[0] = GPIO18 -> relay IN1
+    # DOUT[1] = GPIO19 -> relay IN2
+    #
+    # Low-level trigger relay:
+    #   GPIO HIGH = relay OFF
+    #   GPIO LOW  = relay ON
+    #
+    # Tested hardware behavior:
+    #   IN1 = LOW, IN2 = HIGH -> CLOSE
+    #   IN1 = HIGH, IN2 = LOW -> OPEN
 
     if mode == 1:
-        # OPEN -> DOUT=[0, 1]
+        # OPEN -> logical DOUT=[0, 1]
         dout_shadow = 0b10
 
     elif mode == 2:
-        # CLOSE -> DOUT=[1, 0]
+        # CLOSE -> logical DOUT=[1, 0]
         dout_shadow = 0b01
 
     else:
-        # STOP -> DOUT=[0, 0]
+        # STOP -> logical DOUT=[0, 0]
         dout_shadow = 0b00
 
     # Shadow test mode: do not touch real GPIO pins.
     if not USE_REAL_DOUT:
         return
 
-    # Real output mode.
-    digital_outputs[0].value(0)
-    digital_outputs[1].value(0)
+    # First turn both relays OFF.
+    digital_outputs[0].value(1)  # GPIO18 / IN1 OFF
+    digital_outputs[1].value(1)  # GPIO19 / IN2 OFF
     time.sleep_ms(20)
 
     if mode == 1:
-        # OPEN
-        digital_outputs[1].value(1)
+        # OPEN -> trigger IN2 / GPIO19
+        digital_outputs[1].value(0)
 
     elif mode == 2:
-        # CLOSE
-        digital_outputs[0].value(1)
+        # CLOSE -> trigger IN1 / GPIO18
+        digital_outputs[0].value(0)
 
-    # mode 0 keeps both LOW
+    # mode 0 keeps both HIGH/OFF
 
 
 # ============================================================
@@ -256,12 +269,12 @@ def make_packet():
     for index, pin in enumerate(digital_inputs):
         din_mask |= pin.value() << index
 
-    if USE_REAL_DOUT:
-        dout_mask = 0
-        for index, pin in enumerate(digital_outputs):
-            dout_mask |= pin.value() << index
-    else:
-        dout_mask = dout_shadow
+    # if USE_REAL_DOUT:
+    #     dout_mask = 0
+    #     for index, pin in enumerate(digital_outputs):
+    #         dout_mask |= pin.value() << index
+    # else:
+    dout_mask = dout_shadow
 
     # Packet layout:
     # A5 5A | version | DIN | DOUT | ticks_ms | 10 signed int16 | checksum
diff --git a/pc_reader.py b/pc_reader.py
index e1bc093..94b761b 100644
--- a/pc_reader.py
+++ b/pc_reader.py
@@ -119,3 +119,4 @@ def main():
 
 if __name__ == "__main__":
     main()
+# python3 /home/shun/esp/pc_reader.py /dev/ttyUSB0 --baud 115200
\ No newline at end of file