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@pugzo(pugspapa)

NimBLE-ArduinoによるUARTライクなBLE通信

Last updated at Posted at 2025-10-19

概要

以前、M5StampC3UにてUARTライクなBLE通信を試しましがセキュリティ設定が無いことや、
ライブラリが重いという問題がありました。NimBLEという軽量ライブラリがあることを
知りさっそく試してみました。コードについては生成AIの手を借りています。

セキュリティ設定は下記コードで実装し暗号化も行われます。
NimBLEDevice::setSecurityAuth(true, true, true);　// bonding, MITM, secure

引数 有効時の意味（セキュリティ効果）
bond = true ペアリング情報を保存 次回以降の再接続で即暗号通信
mitm = true 中間者攻撃対策（PINや確認あり） PIN一致が必要になる
secure = true LE Secure Connections方式 AES-128強度の暗号通信

また、1回に送信できる文字数については下記で設定しています。
NimBLEDevice::setMTU(247);
247バイト設定ですが、3バイトはATTヘッダに使われるため
実質244バイト（１バイト文字で244文字）となります。
日本語の２バイト文字も問題無く送受信できています。
これでUARTライクなセキュアBLE通信が確立できました。

image.png
接続待機でLED緑点灯、接続確立で青点灯します。
切断後は再度アドバダイズされるので自動で再接続されます。

image.png
COM10がSever（Peripheral）、COM23がClient（Central）になります。
5秒毎にそれぞれが定期送信を行っています。
また、任意の文字列（test 123,test 456）送信しています。

環境など

　エディタ：VisualStudioCode（PlatformIO IDE）
　マイコン：M5Stamp C3U Mate　2台
　フレームワーク：Aruduino

コード（Server側）　

#include <Arduino.h>
#include <NimBLEDevice.h>
#include <Adafruit_NeoPixel.h>

// ==============================
//  BLE UART Configuration
// ==============================
#define SECURITY_PIN 123456
#define DEVICE_NAME "ESP32C3-BLE-UART"

// ==============================
//  BLE UART Service UUIDs
// ==============================
static const char* SERVICE_UUID           = "6E400001-B5A3-F393-E0A9-E50E24DCCA9E";
static const char* CHARACTERISTIC_UUID_RX = "6E400002-B5A3-F393-E0A9-E50E24DCCA9E";
static const char* CHARACTERISTIC_UUID_TX = "6E400003-B5A3-F393-E0A9-E50E24DCCA9E";

// ==============================
//  Global Variables
// ==============================
NimBLECharacteristic* g_tx = nullptr;
bool g_connected = false;

// ==============================
//  LED Configuration
// ==============================
#define LED_PIN 2
Adafruit_NeoPixel pixels(1, LED_PIN, NEO_GRB + NEO_KHZ800);

// ===================================================
//  BLE Server Callbacks
// ===================================================
class ServerCallbacks : public NimBLEServerCallbacks {
    void onConnect(NimBLEServer* pServer, NimBLEConnInfo& connInfo) override {
        (void)pServer; (void)connInfo;
        g_connected = true;
        Serial.println("✅ Central connected!");
        // BLE接続でLED青点灯
        pixels.setPixelColor(0, pixels.Color(0, 0, 50));
        pixels.show();
    }
    void onDisconnect(NimBLEServer* pServer, NimBLEConnInfo& connInfo, int reason) override {
        (void)pServer; (void)connInfo;
        g_connected = false;
        Serial.printf("❌ Central disconnected (reason=%d)\n", reason);
        // BLE切断でLED緑点灯
        pixels.setPixelColor(0, pixels.Color(0, 50, 0));
        pixels.show();
        // 再度アドバタイズ開始
        NimBLEDevice::getAdvertising()->start();
        Serial.println("🔁 Advertising restarted!");
    }
};

// ===================================================
//  RX Characteristic Callback
// ===================================================
class RxCallbacks : public NimBLECharacteristicCallbacks {
    void onWrite(NimBLECharacteristic* ch, NimBLEConnInfo& info) override {
        (void)info;
        std::string v = ch->getValue();
        if (!v.empty()) {
            Serial.print("📩 RX: "); Serial.println(v.c_str());
        }
    }
};

// ===================================================
//  Setup and Loop
void setup() {
    // Initialize NeoPixel
    pixels.begin();
    pixels.setPixelColor(0, pixels.Color(0, 50, 0));// Green color
    pixels.show();// Turn on LED to indicate startup

    // Initialize Serial
    Serial.begin(115200);
    delay(200);
    Serial.println("🚀 Peripheral Advanced (v2.3.x)");

    // Initialize NimBLE
    NimBLEDevice::init(DEVICE_NAME);

    // Transmit Power
    NimBLEDevice::setPowerLevel(ESP_PWR_LVL_P21, ESP_BLE_PWR_TYPE_ADV);

    // Security (Static PIN, v2.x API) & MTU
    NimBLEDevice::setSecurityAuth(true, true, true);   // bonding, MITM, secure
    NimBLEDevice::setSecurityPasskey(SECURITY_PIN);
    NimBLEDevice::setSecurityIOCap(BLE_HS_IO_DISPLAY_YESNO);
    NimBLEDevice::setMTU(247);  // 実効244 bytes（安定・実装上限）Payload + 3バイト（ATTヘッダ）

    // Create Server
    NimBLEServer* server = NimBLEDevice::createServer();
    server->setCallbacks(new ServerCallbacks());

    // Create Service and Characteristics
    NimBLEService* svc = server->createService(SERVICE_UUID);
    g_tx = svc->createCharacteristic(CHARACTERISTIC_UUID_TX, NIMBLE_PROPERTY::NOTIFY);
    NimBLECharacteristic* rx = svc->createCharacteristic(CHARACTERISTIC_UUID_RX, NIMBLE_PROPERTY::WRITE | NIMBLE_PROPERTY::WRITE_NR);
    rx->setCallbacks(new RxCallbacks());
    svc->start();

    // Start Advertising
    NimBLEAdvertising* adv = NimBLEDevice::getAdvertising();
    NimBLEAdvertisementData advData; advData.addServiceUUID(SERVICE_UUID);
    adv->setAdvertisementData(advData);
    NimBLEAdvertisementData scanData; scanData.setName(DEVICE_NAME); scanData.addServiceUUID(SERVICE_UUID);
    adv->setScanResponseData(scanData);
    adv->setMinInterval(0x20);
    adv->setMaxInterval(0x40);
    adv->start();
    Serial.println("✅ Advertising started!");
}

void loop() {
    static uint32_t last = 0;
    // 定期送信
    if (g_connected && millis() - last > 5000) {
        last = millis();
        const char* msg = "Hello from Peripheral";
        g_tx->setValue(msg);
        g_tx->notify();
    }

    // USBシリアル受信⇒BLE送信
    if(Serial.available()>0){    
        String rev_str = Serial.readStringUntil('\n'); //終端文字までを取得
        g_tx->setValue(rev_str.c_str());
        g_tx->notify();
    }
}
// ===================================================

plathomeio.ini設定（Server）

[env:m5stampc3u]
platform = espressif32
board = esp32-c3-devkitm-1
framework = arduino
build_flags =
-DARDUINO_USB_CDC_ON_BOOT
-DARDUINO_USB_MODE
lib_deps =
h2zero/NimBLE-Arduino @ ^2.3.6
adafruit/Adafruit NeoPixel@^1.12.2

コード（Client側）

#include <Arduino.h>
#include <NimBLEDevice.h>
#include <Adafruit_NeoPixel.h>

// ==============================
//  BLE UART Configuration
// ==============================
#define SECURITY_PIN 123456
#define TARGET_NAME "ESP32C3-BLE-UART"

// =============================
// UUIDs for Nordic UART Service (NUS)
// =============================
static const char* SERVICE_UUID           = "6E400001-B5A3-F393-E0A9-E50E24DCCA9E";
static const char* CHARACTERISTIC_UUID_RX = "6E400002-B5A3-F393-E0A9-E50E24DCCA9E"; // Peripheral RX (write target)
static const char* CHARACTERISTIC_UUID_TX = "6E400003-B5A3-F393-E0A9-E50E24DCCA9E"; // Peripheral TX (notify source)

// ===================================================
//  Global Variables
// ===================================================
static NimBLEAdvertisedDevice* g_adv = nullptr;
static NimBLEClient* g_client = nullptr;
static NimBLERemoteCharacteristic* g_remoteTx = nullptr; // subscribe
static NimBLERemoteCharacteristic* g_remoteRx = nullptr; // write target
static bool g_connected = false;
static bool g_doConnect = false;
static void startScan();

// ==============================
//  LED Configuration
// ==============================
#define LED_PIN 2
Adafruit_NeoPixel pixels(1, LED_PIN, NEO_GRB + NEO_KHZ800);

// ===================================================
//  Notification Callback
// ===================================================
static void notifyCB(NimBLERemoteCharacteristic* pChar, uint8_t* pData, size_t len, bool isNotify) {
  (void)pChar; (void)isNotify;
  String s; s.reserve(len + 1);
  for (size_t i=0;i<len;i++) s += (char)pData[i];
  //log_json("rx", s.c_str(), (g_client ? g_client->getRssi() : 0));
  Serial.print("📩 RX: "); Serial.println(s);
}


// ===================================================
//  BLE Client Callbacks
// ===================================================
class ClientCallbacks : public NimBLEClientCallbacks {
  void onConnect(NimBLEClient* pClient) override {
    (void)pClient;
    Serial.println("✅ Connected!");
    // BLE接続でLED青点灯
    pixels.setPixelColor(0, pixels.Color(0, 0, 50));
    pixels.show();
  }
  void onDisconnect(NimBLEClient* pClient, int reason) override {
    (void)pClient;
    g_connected = false;
    Serial.printf("❌ Disconnected (reason=%d)\n", reason);
    // BLE切断でLED緑点灯
    pixels.setPixelColor(0, pixels.Color(0, 50, 0));
    pixels.show();
    // 再度スキャン開始
    startScan();
  }
};

// ===================================================
//  BLE Scan Callbacks
// ===================================================
class MyScanCallbacks : public NimBLEScanCallbacks {
  void onResult(const NimBLEAdvertisedDevice* dev) override {
    bool matchUuid = dev->haveServiceUUID() && dev->isAdvertisingService(NimBLEUUID(SERVICE_UUID));
    bool matchName = !std::string(TARGET_NAME).empty() && (dev->getName() == std::string(TARGET_NAME));
    Serial.printf("🔎 Found: %s RSSI=%d UUIDmatch=%d Namematch=%d\n",
                  dev->getName().c_str(), dev->getRSSI(), matchUuid, matchName);
    if (matchUuid || matchName) {
      Serial.println("🎯 Target found, stopping scan...");
      NimBLEDevice::getScan()->stop();
      g_adv = (NimBLEAdvertisedDevice*)dev;
      g_doConnect = true;
    }
  }
};

// ===================================================
//  Connect to Server
// ===================================================
static bool connectToServer() {
  if (!g_adv) return false;
  g_client = NimBLEDevice::createClient();
  g_client->setClientCallbacks(new ClientCallbacks(), false);

  NimBLEDevice::setSecurityAuth(true, true, true);
  NimBLEDevice::setSecurityPasskey(SECURITY_PIN);
  NimBLEDevice::setSecurityIOCap(BLE_HS_IO_DISPLAY_YESNO);

  Serial.printf("🔗 Connecting to %s\n", g_adv->getName().c_str());
  if (!g_client->connect(g_adv)) {
    Serial.println("❌ Connection failed.");
    return false;
  }

  NimBLERemoteService* svc = g_client->getService(SERVICE_UUID);
  if (!svc) {
    Serial.println("❌ Service not found!");
    g_client->disconnect();
    return false;
  }

  g_remoteTx = svc->getCharacteristic(CHARACTERISTIC_UUID_TX);
  if (g_remoteTx && g_remoteTx->canNotify()) g_remoteTx->subscribe(true, notifyCB);

  g_remoteRx = svc->getCharacteristic(CHARACTERISTIC_UUID_RX);
  if (!g_remoteRx || !g_remoteRx->canWrite()) {
    g_client->disconnect();
    return false;
  }

  g_connected = true;
  Serial.println("✅ Ready!");
  return true;
}

// ===================================================
//  Start Scan
// ===================================================
static void startScan() {
  NimBLEScan* scan = NimBLEDevice::getScan();
  scan->setScanCallbacks(new MyScanCallbacks(), false);
  scan->setActiveScan(true);
  scan->start(0, false);
  Serial.println("🔍 Scanning...");
}

// ===================================================
//  Setup and Loop
void setup() {
  // Initialize NeoPixel
  pixels.begin();
  pixels.setPixelColor(0, pixels.Color(0, 50, 0));// Green color
  pixels.show();// Turn on LED to indicate startup
  Serial.begin(115200);
  delay(200);
  Serial.println("🚀 Central Advanced (Renamed)");
  NimBLEDevice::init("ESP32C3-Central-Adv");
  // Transmit Power
  NimBLEDevice::setPowerLevel(ESP_PWR_LVL_P21, ESP_BLE_PWR_TYPE_ADV);
  NimBLEDevice::setMTU(247);  // 実効244 bytes（安定・実装上限）Payload + 3バイト（ATTヘッダ）
  startScan();
}

void loop() {
  // Handle Connection
  if (g_doConnect) {
    g_doConnect = false;
    if (!connectToServer()) {
      delay(500);// Wait before retrying
      startScan();
    }
  }

  // 定期送信処理
  if (g_connected && g_remoteRx) {
    static uint32_t lastTx = 0;
    if (millis() - lastTx > 5000) {
      lastTx = millis();
      const char* msg = "Hello from Central";
      g_remoteRx->writeValue((uint8_t*)msg, strlen(msg), false);
    }
  }

  // USBシリアル受信⇒BLE送信処理
  if(Serial.available()>0){    
    String rev_str = Serial.readStringUntil('\n'); //終端文字までを取得
    g_remoteRx->writeValue((uint8_t*)rev_str.c_str(), strlen(rev_str.c_str()), false);
  }
  delay(20);
}
// ===================================================

plathomeio.ini設定（Client）

[env:m5stampc3u]
platform = espressif32
board = esp32-c3-devkitm-1
framework = arduino
build_flags =
-DARDUINO_USB_CDC_ON_BOOT
-DARDUINO_USB_MODE
lib_deps =
h2zero/NimBLE-Arduino @ ^2.3.6
adafruit/Adafruit NeoPixel@^1.12.2

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