If you are not familiar with Central Role, it is advised to look at the "Central BLEUART" example first then continue with this afterwards.
This example demonstrates how you can use a Feather nRF52/nRF52840 to connect to two other Bluefruit or BLE devices using the bleuart (AKA 'NUS') service concurrently, with the device running at both a peripheral and a central at the same time.
This dual role example acts as a BLE bridge that sits between a central and a peripheral forwarding bleuart messages back and forth, as shown in the image below:
Server & Client Service Setup
Since the Bluefruit device will act as both a central and a peripheral, we will need to declare both server and client instance of the bleuart helper class:
// Peripheral uart service BLEUart bleuart; // Central uart client BLEClientUart clientUart;
Before we can configure client services, Bluefruit.begin() must be called with at least 1 for the number of concurrent connection for both peripheral and central mode:
// Initialize Bluefruit with max concurrent connections as Peripheral = 1, Central = 1 Bluefruit.begin(1, 1);
After this, client services must be initialized by calling their begin() function, followed by any callbacks that you wish to wire up as well:
// Configure and Start BLE Uart Service bleuart.begin(); bleuart.setRxCallback(prph_bleuart_rx_callback); // Init BLE Central Uart Serivce clientUart.begin(); clientUart.setRxCallback(cent_bleuart_rx_callback);
We are then ready to forward data from central to peripheral and vice versa using callbacks:
void cent_bleuart_rx_callback(BLEClientUart& cent_uart)
{
char str[20+1] = { 0 };
cent_uart.read(str, 20);
Serial.print("[Cent] RX: ");
Serial.println(str);
if ( bleuart.notifyEnabled() )
{
// Forward data from our peripheral to Mobile
bleuart.print( str );
}else
{
// response with no prph message
clientUart.println("[Cent] Peripheral role not connected");
}
}
void prph_bleuart_rx_callback(void)
{
// Forward data from Mobile to our peripheral
char str[20+1] = { 0 };
bleuart.read(str, 20);
Serial.print("[Prph] RX: ");
Serial.println(str);
if ( clientUart.discovered() )
{
clientUart.print(str);
}else
{
bleuart.println("[Prph] Central role not connected");
}
}
Peripheral Role
The first thing to do for the peripheral part of our code is to setup the connect callback, which fires when a connection is established/disconnected with the central. Alternatively you could poll the connection status with connected(), but callbacks helps to simplify the code significantly:
// Callbacks for Peripheral Bluefruit.setConnectCallback(prph_connect_callback); Bluefruit.setDisconnectCallback(prph_disconnect_callback);
Central Role
Next we setup the Central mode connect callback, which fires when a connection is established/disconnected with a peripheral device:
// Callbacks for Central Bluefruit.Central.setConnectCallback(cent_connect_callback); Bluefruit.Central.setDisconnectCallback(cent_disconnect_callback);
Advertising and Scanner
It is possible to start both the scanner and advertising at the same time so that we can discover and be discovered by other BLE devices. For the scanner, we use a filter that only fires the callback if a specific UUID is found in the advertising data of the peer device:
/* Start Central Scanning * - Enable auto scan if disconnected * - Interval = 100 ms, window = 80 ms * - Filter only accept bleuart service * - Don't use active scan * - Start(timeout) with timeout = 0 will scan forever (until connected) */ Bluefruit.Scanner.setRxCallback(scan_callback); Bluefruit.Scanner.restartOnDisconnect(true); Bluefruit.Scanner.setInterval(160, 80); // in unit of 0.625 ms Bluefruit.Scanner.filterUuid(bleuart.uuid); Bluefruit.Scanner.useActiveScan(false); Bluefruit.Scanner.start(0); // 0 = Don't stop scanning after n seconds // Advertising packet Bluefruit.Advertising.addFlags(BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE); Bluefruit.Advertising.addTxPower(); // Include bleuart 128-bit uuid Bluefruit.Advertising.addService(bleuart); // Secondary Scan Response packet (optional) // Since there is no room for 'Name' in Advertising packet Bluefruit.ScanResponse.addName(); /* Start Advertising * - Enable auto advertising if disconnected * - Interval: fast mode = 20 ms, slow mode = 152.5 ms * - Timeout for fast mode is 30 seconds * - Start(timeout) with timeout = 0 will advertise forever (until connected) * * For recommended advertising interval * https://developer.apple.com/library/content/qa/qa1931/_index.html */ Bluefruit.Advertising.restartOnDisconnect(true); Bluefruit.Advertising.setInterval(32, 244); // in unit of 0.625 ms Bluefruit.Advertising.setFastTimeout(30); // number of seconds in fast mode Bluefruit.Advertising.start(0); // 0 = Don't stop advertising after n seconds
/*********************************************************************
This is an example for our nRF52 based Bluefruit LE modules
Pick one up today in the adafruit shop!
Adafruit invests time and resources providing this open source code,
please support Adafruit and open-source hardware by purchasing
products from Adafruit!
MIT license, check LICENSE for more information
All text above, and the splash screen below must be included in
any redistribution
*********************************************************************/
/*
* This sketch demonstrate how to run both Central and Peripheral roles
* at the same time. It will act as a relay between an central (mobile)
* to another peripheral using bleuart service.
*
* Mobile <--> DualRole <--> peripheral Ble Uart
*/
#include <bluefruit.h>
// OTA DFU service
BLEDfu bledfu;
// Peripheral uart service
BLEUart bleuart;
// Central uart client
BLEClientUart clientUart;
void setup()
{
Serial.begin(115200);
while ( !Serial ) delay(10); // for nrf52840 with native usb
Serial.println("Bluefruit52 Dual Role BLEUART Example");
Serial.println("-------------------------------------\n");
// Initialize Bluefruit with max concurrent connections as Peripheral = 1, Central = 1
// SRAM usage required by SoftDevice will increase with number of connections
Bluefruit.begin(1, 1);
Bluefruit.setTxPower(4); // Check bluefruit.h for supported values
// Callbacks for Peripheral
Bluefruit.Periph.setConnectCallback(prph_connect_callback);
Bluefruit.Periph.setDisconnectCallback(prph_disconnect_callback);
// Callbacks for Central
Bluefruit.Central.setConnectCallback(cent_connect_callback);
Bluefruit.Central.setDisconnectCallback(cent_disconnect_callback);
// To be consistent OTA DFU should be added first if it exists
bledfu.begin();
// Configure and Start BLE Uart Service
bleuart.begin();
bleuart.setRxCallback(prph_bleuart_rx_callback);
// Init BLE Central Uart Serivce
clientUart.begin();
clientUart.setRxCallback(cent_bleuart_rx_callback);
/* Start Central Scanning
* - Enable auto scan if disconnected
* - Interval = 100 ms, window = 80 ms
* - Filter only accept bleuart service
* - Don't use active scan
* - Start(timeout) with timeout = 0 will scan forever (until connected)
*/
Bluefruit.Scanner.setRxCallback(scan_callback);
Bluefruit.Scanner.restartOnDisconnect(true);
Bluefruit.Scanner.setInterval(160, 80); // in unit of 0.625 ms
Bluefruit.Scanner.filterUuid(bleuart.uuid);
Bluefruit.Scanner.useActiveScan(false);
Bluefruit.Scanner.start(0); // 0 = Don't stop scanning after n seconds
// Set up and start advertising
startAdv();
}
void startAdv(void)
{
// Advertising packet
Bluefruit.Advertising.addFlags(BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE);
Bluefruit.Advertising.addTxPower();
// Include bleuart 128-bit uuid
Bluefruit.Advertising.addService(bleuart);
// Secondary Scan Response packet (optional)
// Since there is no room for 'Name' in Advertising packet
Bluefruit.ScanResponse.addName();
/* Start Advertising
* - Enable auto advertising if disconnected
* - Interval: fast mode = 20 ms, slow mode = 152.5 ms
* - Timeout for fast mode is 30 seconds
* - Start(timeout) with timeout = 0 will advertise forever (until connected)
*
* For recommended advertising interval
* https://developer.apple.com/library/content/qa/qa1931/_index.html
*/
Bluefruit.Advertising.restartOnDisconnect(true);
Bluefruit.Advertising.setInterval(32, 244); // in unit of 0.625 ms
Bluefruit.Advertising.setFastTimeout(30); // number of seconds in fast mode
Bluefruit.Advertising.start(0); // 0 = Don't stop advertising after n seconds
}
void loop()
{
// do nothing, all the work is done in callback
}
/*------------------------------------------------------------------*/
/* Peripheral
*------------------------------------------------------------------*/
void prph_connect_callback(uint16_t conn_handle)
{
// Get the reference to current connection
BLEConnection* connection = Bluefruit.Connection(conn_handle);
char peer_name[32] = { 0 };
connection->getPeerName(peer_name, sizeof(peer_name));
Serial.print("[Prph] Connected to ");
Serial.println(peer_name);
}
void prph_disconnect_callback(uint16_t conn_handle, uint8_t reason)
{
(void) conn_handle;
(void) reason;
Serial.println();
Serial.println("[Prph] Disconnected");
}
void prph_bleuart_rx_callback(uint16_t conn_handle)
{
(void) conn_handle;
// Forward data from Mobile to our peripheral
char str[20+1] = { 0 };
bleuart.read(str, 20);
Serial.print("[Prph] RX: ");
Serial.println(str);
if ( clientUart.discovered() )
{
clientUart.print(str);
}else
{
bleuart.println("[Prph] Central role not connected");
}
}
/*------------------------------------------------------------------*/
/* Central
*------------------------------------------------------------------*/
void scan_callback(ble_gap_evt_adv_report_t* report)
{
// Since we configure the scanner with filterUuid()
// Scan callback only invoked for device with bleuart service advertised
// Connect to the device with bleuart service in advertising packet
Bluefruit.Central.connect(report);
}
void cent_connect_callback(uint16_t conn_handle)
{
// Get the reference to current connection
BLEConnection* connection = Bluefruit.Connection(conn_handle);
char peer_name[32] = { 0 };
connection->getPeerName(peer_name, sizeof(peer_name));
Serial.print("[Cent] Connected to ");
Serial.println(peer_name);;
if ( clientUart.discover(conn_handle) )
{
// Enable TXD's notify
clientUart.enableTXD();
}else
{
// disconnect since we couldn't find bleuart service
Bluefruit.disconnect(conn_handle);
}
}
void cent_disconnect_callback(uint16_t conn_handle, uint8_t reason)
{
(void) conn_handle;
(void) reason;
Serial.println("[Cent] Disconnected");
}
/**
* Callback invoked when uart received data
* @param cent_uart Reference object to the service where the data
* arrived. In this example it is clientUart
*/
void cent_bleuart_rx_callback(BLEClientUart& cent_uart)
{
char str[20+1] = { 0 };
cent_uart.read(str, 20);
Serial.print("[Cent] RX: ");
Serial.println(str);
if ( bleuart.notifyEnabled() )
{
// Forward data from our peripheral to Mobile
bleuart.print( str );
}else
{
// response with no prph message
clientUart.println("[Cent] Peripheral role not connected");
}
}
Page last edited January 22, 2025
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