diff --git a/mozc-piropiro/README.md b/mozc-piropiro/README.md
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+Copyright 2015 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+
+ Summary
+=====================================
+
+Mechanical design, circuit diagram and firmware of Google Japanese Input
+piropiro version.
+
+
+ Files
+=====================================
+
+* stl/*  -- 3D shape data of mechanical parts
+* README.txt  -- this file
+* circuit.png -- Circuit diagram
+* assembly.png -- Mechanical assembly instruction
+* arduino/piropiro/piropiro.ino -- Firmware source code (Arduino sketch)
+
+
+ Building your device
+=====================================
+
+## Mechanical parts
+
+Output all mechanical parts under stl/ directory with a 3D printer.
+Additionally, you need these parts.
+
+* M2x4 scerws  x7
+* M2 washer (inside diameter=2.2mm, outside diameter=5.8mm)  x1
+* A party horn  x1
+
+## Electronic parts
+
+* Arduino Nano
+    Some other models of Arduino (e.g. Arduino Uno) can be used
+    if required function is available.
+* RN-42-EK or a compatible evaluation kit
+    RN-42 can be used instead if wired appropriately.
+* GP2Y0E02A distance sensor
+* 1/8W Resistors
+    * 1k
+    * 470
+* Breadboard and jump wires
+
+## Assembly
+
+See the circuit diagram and mechanical assembly instruction images.
+
+## RN42 module configuration
+
+This step is required for the first time, or when changing the device's name.
+Note that you should not connect Arduino Nano when you configure RN-42-EK via
+USB, because signal from Arduino Nano overrides the TxD signal on RN-42-EK.
+See Microchip's documents for detail.
+
+1. Connect RN-42-EK to your PC by USB.
+2. Run a terminal emulator and open the serial port for RN-42-EK.
+3. Type '$$$'. Make sure 'CMD' is returned from RN-42-EK and the green LED on
+   RN-42-EK blinks fast.
+4. Configure the module by these commands:
+
+* * * * * *
+    SU,115k
+    SM,6
+    SA,2
+    S~,6
+    SH,0000
+    SN,MY_PIROPIRO_KEYBOARD
+    R,1
+* * * * * *
+MY\_PIROPIRO\_KEYBOARD is a device name that will appear when you scan Bluetooth
+devices, and can be replaced by your preferred name.
+
+The commands will configure the module as follows:
+
+* 115200bps
+* Pairing mode
+* SSP "just works" mode
+* SPP profile
+* HID flag register = 0 (keyboard)
+
+
+## Electronic Circuit Assembly
+
+See the circuit diagram for detail.
+When operating the device, supply power by USB cables to both RN-42-EK and
+Arduino Nano. You can alternatively supply 3.3V power to RN-42-EK from Arduino's
+3.3V pin, but this requires a modification on RN-42-EK to disconnect the
+regulator's output pin on it from the circuit.
+
+
+ Using piropiro input
+=====================================
+
+## Sensor adjustment
+
+1. Attach the device to your party horn. The sensor should be positioned about
+40mm apart from the rolled paper tube.
+2. Turn on Arduino Nano and adjust the optical axis of the sensor. The LED on
+Arduino board is lit while the sensor is collectly sensing the tip of the
+paper tube between 50mm -- 350mm.
+
+
+## Bluetooth pairing
+
+Using your device (e.g. Android phone), scan Bluetooth devices and you will
+find MY\_PIROPIRO\_KEYBOARD (or the name you set up) in the available device
+list.
+
+## How to input
+
+Switch the Japanese IME on the paired device to romaji input mode.
+Characters will be input as you blow the horn.
+The length of the horn chooses the vowel.
+In order to switch to the next column (consonant), quickly shrink the horn and blow it again.
diff --git a/mozc-piropiro/arduino/piropiro/piropiro.ino b/mozc-piropiro/arduino/piropiro/piropiro.ino
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+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * Firmware of piropiro (party horn) Bluetooth keyboard.
+ */
+
+#define V_REF 5.0
+#define PIN_LED 13
+#define N_AD_SAMPLES 10
+
+#define INTERVAL_MSEC 20
+#define COMMIT_TIME (600 / INTERVAL_MSEC)
+
+#define ROWS 5
+#define COLS 9
+
+const char* characters[ROWS * COLS] = {
+  "a", "i", "u", "e", "o",
+  "ka", "ki", "ku", "ke", "ko",
+  "sa", "si", "su", "se", "so",
+  "ta", "ti", "tu", "te", "to",
+  "na", "ni", "nu", "ne", "no",
+  "ha", "hi", "hu", "he", "ho",
+  "ma", "mi", "mu", "me", "mo",
+  "ya", "ya", "yu", "yu", "yo",
+  "wa", "wo", "nn", ",", "."
+};
+
+int column = 0;
+int vowel = 0;
+int release_duration = 0;
+
+void setup() {
+  Serial.begin(115200);
+  pinMode(PIN_LED, OUTPUT);
+  column = 0;
+  vowel = 0;
+}
+
+float getVoltage(int ch) {
+  return analogRead(ch) * V_REF / 1023;
+}
+
+float getAverageVoltage(int ch) {
+  float sum = 0.0;
+  for (int i = 0; i < N_AD_SAMPLES; i++) {
+    sum += getVoltage(ch);
+  }
+  return sum / N_AD_SAMPLES;
+}
+
+float voltageToLength(float voltage) {
+  return 648 - voltage * 268;
+}
+
+void loop() {
+  float length = voltageToLength(getAverageVoltage(0));
+  if (length > 350) {
+    digitalWrite(PIN_LED, LOW);
+  } else {
+    digitalWrite(PIN_LED, HIGH);
+    if (length < 50) {
+      if (vowel > 0) {
+        vowel = 0;
+        column ++;
+        if (column >= COLS) {
+          column = 0;
+        }
+        release_duration = 0;
+      } else if (release_duration > COMMIT_TIME) {
+        vowel = 0;
+        column = 0;
+      } else if (column > 0) {
+        release_duration ++;
+      }
+    } else {
+      int target_vowel = (length - 80) / 40 + 1;
+      if (target_vowel > 5) target_vowel = 5;
+      if (vowel < target_vowel) {
+        if (column > 0 || vowel > 0) {
+          Serial.print("\b");
+        }
+        vowel ++;
+        int current_character = vowel - 1 + column * 5;
+        Serial.print(characters[current_character]);
+      }
+    }
+  }
+  delay(INTERVAL_MSEC);
+}
+
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