diff --git a/README.md b/README.md
new file mode 100644
index 0000000..810d518
--- /dev/null
+++ b/README.md
@@ -0,0 +1,10 @@
+# Gateway & sensors
+
+## Branches
+Each sensor has a dedicated branch. E.g.:
+* temp_sensor
+* oil_sensor
+
+The gateway uses `master` as the main branch. Other sensors' branches get merged once they are ready for production.
+
+## Release flow
diff --git a/gateway/include/Protocol_Doorbell.h b/gateway/include/Protocol_Doorbell.h
index 21609d3..2ad6b76 100644
--- a/gateway/include/Protocol_Doorbell.h
+++ b/gateway/include/Protocol_Doorbell.h
@@ -60,8 +60,12 @@ private:
     void preamble() {
         noInterrupts();
         for (int i = 0; i < 370; i++) {
-            transmitBit(HIGH);
-            transmitBit(LOW);
+            // transmitBit(HIGH);
+            // transmitBit(LOW);
+            PORTB |= _BV(PORT_BIT);   // HIGH
+            _delay_us(BIT_LENGTH);
+            PORTB &= ~_BV(PORT_BIT);  // LOW
+            _delay_us(BIT_LENGTH);
         }
         interrupts();
     }