Bluetooth

Enable energy-efficient wireless communication with your Echo using Bluetooth Low Energy (BLE).

BLE Server Library Documentation

Overview

The BLE Server Library provides a simplified interface for creating Bluetooth Low Energy servers on the Echo. BLE is optimized for low power consumption and ideal for wireless control and data exchange in robotics applications.

Method	Description
BLEServerWrapper(name)	Creates a BLE server with the specified device name
begin()	Initializes the BLE subsystem (call once in setup)
connect()	Starts advertising and makes device discoverable
disconnect()	Stops connection and advertising
getStatus()	Returns true if a client is connected, false otherwise
autoReconnect(enable)	Enables or disables automatic reconnection after disconnect
sendData(data)	Sends string data to the connected client
readData()	Retrieves received data from client (clears after reading)
loop()	Handles reconnection and BLE management (call in main loop)

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Quick Start Example

#include <EchoLib.h>

BLEServerWrapper ble("EchoBot");

void setup() {
  Serial.begin(115200);
  ble.begin();
  ble.connect();
}

void loop() {
  ble.loop();
  
  if (ble.getStatus()) {
    String cmd = ble.readData();
    if (cmd == "PING") {
      ble.sendData("PONG");
    }
  }
  
  delay(100);
}

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Method Details

Constructor

BLEServerWrapper(const String& name)

Creates a BLE server with the specified advertised name. This name will be visible when scanning for BLE devices.

BLEServerWrapper ble("EchoRobot");

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Initialization

void begin()

Initializes the BLE communication stack. Must be called once in setup() before any other BLE operations.

void setup() {
  Serial.begin(115200);
  ble.begin();
}

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Connection Management

void connect()

Starts BLE advertising, making the device discoverable to nearby BLE clients.

ble.connect();  // Device is now discoverable

void disconnect()

Stops the current connection and advertising. Useful for low-power modes or resetting connections.

ble.disconnect();

bool getStatus()

Returns the current connection state.

if (ble.getStatus()) {
  Serial.println("Client connected!");
}

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Auto-Reconnection

void autoReconnect(bool enable)

Enables or disables automatic reconnection. When enabled (default), the server automatically resumes advertising after disconnection.

ble.autoReconnect(true);   // Auto-reconnect on (default)
ble.autoReconnect(false);  // Manual control only

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Data Communication

void sendData(const String& data)

Transmits string data to the connected client. Only works when a client is connected.

if (ble.getStatus()) {
  ble.sendData("Some String of data");
}

String readData()

Retrieves the most recent data received from the client. Returns an empty string if no new data. Data is automatically cleared after reading.

String command = ble.readData();
if (command.length() > 0) {
  Serial.println("Received: " + command);
}

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Loop Management

void loop()

Handles automatic reconnection and internal BLE state management. Must be called regularly in the main loop.

void loop() {
  ble.loop();
  // Your code here
}

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Complete Example

This example demonstrates LED control via BLE with status reporting.

#include <EchoLib.h>

BLEServerWrapper ble("EchoRobot");
const int LED = 2;

void setup() {
  Serial.begin(115200);
  pinMode(LED, OUTPUT);
  
  ble.begin();
  ble.autoReconnect(true);
  ble.connect();
  
  Serial.println("BLE Server Ready");
}

void loop() {
  ble.loop();
  
  if (ble.getStatus()) {
    // Read incoming commands
    String cmd = ble.readData();
    
    if (cmd == "ON") {
      digitalWrite(LED, HIGH);
      ble.sendData("LED is ON");
    } 
    else if (cmd == "OFF") {
      digitalWrite(LED, LOW);
      ble.sendData("LED is OFF");
    }
    else if (cmd == "STATUS") {
      ble.sendData("Online");
    }
    
    // Periodic status update
    static unsigned long lastUpdate = 0;
    if (millis() - lastUpdate > 5000) {
      ble.sendData("Uptime: " + String(millis()/1000) + "s");
      lastUpdate = millis();
    }
  }
  
  delay(100);
}

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Testing with nRF Connect

Connection Steps

1. Scan and Connect

   • Open nRF Connect mobile app

   • Scan for devices

   • Find your device name (e.g., "EchoBot")

   • Tap CONNECT

2. Enable Notifications

   • Expand service: 4fafc201-1fb5-459e-8fcc-c5c9c331914b

   • Find TX Characteristic: beb5483e...

   • Tap the notification icon (down arrow)

   • You'll now receive data from the Echo

3. Send Commands

   • Find RX Characteristic: a4488e9d...

   • Tap the write icon

   • Select "Text" format

   • Type your command (e.g., "ON")

   • Tap "Send"

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Important Notes

Connection Management

Always check connection status before sending data:

if (ble.getStatus()) {
  ble.sendData("Data");
} else {
  Serial.println("Not connected");
}

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Data Size

Keep transmitted data concise for optimal performance. BLE has a limited packet size (20-244 bytes depending on MTU negotiation).

Good: "battery:85,temp:42" Avoid: Large multi-line messages or rapid sequential sends

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Loop Delays

Always include delays in your main loop to maintain BLE stability:

void loop() {
  ble.loop();
  // Your code
  delay(100);  // Essential for stable operation
}

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Initialization Order

Always call begin() before connect():

void setup() {
  Serial.begin(115200);
  ble.begin();      // Initialize first
  ble.connect();    // Then start advertising
}

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Data Clearing

readData() clears data after reading. Store the value if needed later:

String cmd = ble.readData();  // Data is cleared after this
if (cmd == "START") {
  // Use cmd here
}

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Power Consumption

BLE is low-power, but consider these typical current draws:

• Advertising: ~15-20 mA

• Connected (idle): ~8-12 mA

• Connected (active): ~12-18 mA

For extended range, consider using an external IPEX-1 antenna.

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Troubleshooting

Device Not Discoverable

• Verify both begin() and connect() are called

• Check Serial Monitor for initialization messages

• Restart the scanning app

• Ensure no other device is using the same name

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Connection Drops

• Enable auto-reconnect: ble.autoReconnect(true)

• Verify stable power supply

• Reduce distance between devices

• Check for motor-induced electrical interference

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No Data Received

• Confirm connection with getStatus()

• Enable notifications in your BLE client app

• Verify correct characteristic (TX for receiving)

• Check data format

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Unexpected Resets

• Add delay(1000) after Serial.begin()

• Monitor power during motor operation

• Verify adequate power supply

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Technical Specifications

UUIDs

• Service: 4fafc201-1fb5-459e-8fcc-c5c9c331914b

• TX Characteristic: beb5483e-36e1-4688-b7f5-ea07361b26a8 (Notify)

• RX Characteristic: a4488e9d-3c11-42fd-89c8-3ae3a57395e6 (Write)

Configuration

• Data Encoding: UTF-8 strings

• MTU Range: 20-244 bytes (negotiated)

• I2C Pins: 17 (SDA), 18 (SCL) at 400kHz