Communicate two microcontrollers via BLE

[msu7xi]

Hello,

I'm using a nRF52 DK to test BLE communication with another microcontroller. What I need to test is the nRF52 pairing with another brand microcontroller, send a data stream and close the connection.

Could you please tell me which example from the Bluetooth samples list I can use for starting?

Thanks for your attention.

Regards,

[haakonsh]

The Bluetooth: Central / Heart-rate Monitor sample should be a good start.

[msu7xi]

Hello haakonsh,

Thank you very much. I've reviewed this example and it is supposed to connect with the first device with an strong signal. Is there a way to force the board to connect with the device with a given MAC address?

[msu7xi]

I have not implemented NUS GATT server on the ESP32. The ESP32 already has a 128-bit UUID (0000-FFFF-0000-1000-8000-00805f9b34fb) which allows sending/receiving data strings. This works with a mobile application and what I'm trying to do is to make work the nRF52 the same way the mobile application works on the smartphone.

[haakonsh]

Unknown said:

The ESP32 already has a 128-bit UUID (0000-FFFF-0000-1000-8000-00805f9b34fb) which allows sending/receiving data strings.

The Nordic Uart Service uses two characteristics though, rx and tx. If you're only going to use one characteristic for both sending and receiving data then the NUS is not really suited for this task. You should rather implement the service you're already using on the ESP32 in on the nRF52, or modify the service running on the ESP32 to fit the NUS. You can change the UUID's of the NUS to whatever you want btw.

[msu7xi]

Unknown said:

What exactly have you done? I configured the NUS service on the 'central' example and added a call to the 'bt_nus_client_send' function to permanently send data after the device has been connected to the ESP32. I have also modified the NUS 128-bit UUID to the UUID already set in the ESP32 device (0000-FFFF-0000-1000-8000-00805f9b34fb)

I have already modified the UUID of the NUS but I get the error message:

haakonsh said:

-128 = ENOTCONN  "Socket is not connected".

Could it be that there is something else that needs to be configured in the 'prj.conf' file?

[haakonsh]

Unknown said:

Could it be that there is something else that needs to be configured in the 'prj.conf' file?

I don't know. 

Can you share your code, relevant to the bt_nus_client_send error?

[msu7xi]

I have modified the "central_uart" project as follows:

-In the function 'scan_init' (main.c file) the filtering is done by MAC (ESP32's MAC is 60:55:F9:F5:29:D2):

static int scan_init(void)
{
	int err;
	struct bt_scan_init_param scan_init = {
		.connect_if_match = 1,
	};

	uint8_t esp_add[BT_ADDR_SIZE] = {0x60, 0x55, 0xF9, 0xF5, 0x29, 0xD2};
	bt_addr_le_t esp32_address = {
		.type = BT_ADDR_LE_PUBLIC,
		.a = esp_add,
	};

	printk("scan_init\n");
	bt_scan_init(&scan_init);
	bt_scan_cb_register(&scan_cb);

	//err = bt_scan_filter_add(BT_SCAN_FILTER_TYPE_UUID, BT_UUID_NUS_SERVICE);
	//err = bt_scan_filter_add(BT_SCAN_FILTER_TYPE_ADDR, esp32_address);
	err = bt_scan_filter_add(BT_SCAN_FILTER_TYPE_ADDR, /*(const void*)*/esp_add);
	if (err) {
		LOG_ERR("Scanning filters cannot be set (err %d)", err);
		printk("Scanning filters cannot be set (err %d)\n", err);
		return err;
	}

	//err = bt_scan_filter_enable(BT_SCAN_UUID_FILTER, false);
	err = bt_scan_filter_enable(BT_SCAN_ADDR_FILTER, true);
	
	if (err) {
		LOG_ERR("Filters cannot be turned on (err %d)", err);
		printk("Filters cannot be turned on (err %d)\n", err);
		return err;
	}

	LOG_INF("Scan module initialized");
	printk("Scan module initialized\n");
	return err;
}

-In the 'main' function (main.c) I have modified the loop as follows:

for (;;) {
		/* Wait indefinitely for data to be sent over Bluetooth */
		//struct uart_data_t *buf = k_fifo_get(&fifo_uart_rx_data,
		//				     K_FOREVER);

		struct uart_data_t *buf;
		buf->data[0] = 0;
		buf->data[1] = 1;
		buf->data[2] = 2;
		buf->len = 3;

		err = bt_nus_client_send(&nus_client, buf->data, buf->len);
		if (err) {
			LOG_WRN("Failed to send data over BLE connection"
				"(err %d)", err);
			//printk("Failed to send data over BLE connection"
			//	"(err %d)\n", err);
		}

		err = k_sem_take(&nus_write_sem, NUS_WRITE_TIMEOUT);
		if (err) {
			LOG_WRN("NUS send timeout");
			//printk("NUS send timeout\n");
		}
	}

This time the 'bt_nus_client_send' function returns the -128 error as the nRF52 cannot connect to the ESP32. is there something missing in how I have configured the filtering function?

-In the nus.h file I have modified the UUID as follows:

/** @brief UUID of the NUS Service. **/
#define BT_UUID_NUS_VAL \
	BT_UUID_128_ENCODE(0x0000FFFF, 0x0000, 0x1000, 0x8000, 0x00805F9B34FB)

/** @brief UUID of the TX Characteristic. **/
#define BT_UUID_NUS_TX_VAL \
	BT_UUID_128_ENCODE(0x0000FF01, 0x0000, 0x1000, 0x8000, 0x00805F9B34FB)

/** @brief UUID of the RX Characteristic. **/
#define BT_UUID_NUS_RX_VAL \
	BT_UUID_128_ENCODE(0x0000FF02, 0x0000, 0x1000, 0x8000, 0x00805F9B34FB)

[haakonsh]

Where do you set 'nus_client.conn' to point to the connection object of the ESP32 connection?

[msu7xi]

I am not sure which function should set 'nus_client.conn'. Where is this set in the "central_uart" example? I am using this example as template to modify.

[haakonsh]

This is explained in https://academy.nordicsemi.com/lessons/lesson-3-bluetooth-le-connections/ 

[msu7xi]

Excuse me but this is not clear to me. There is no use of NUS library in lesson 3.

haakonsh said:

Where do you set 'nus_client.conn' to point to the connection object of the ESP32 connection?

Do you mean implementing the callback functions?

/* STEP 2.2 - Implement the callback functions */
void on_connected(struct bt_conn *conn, uint8_t err)
{
    if (err) {
        LOG_ERR("Connection error %d", err);
        return;
    }
    LOG_INF("Connected");
    my_conn = bt_conn_ref(conn);

	/* STEP 3.2  Turn the connection status LED on */
    dk_set_led(CONNECTION_STATUS_LED, 1);
}

void on_disconnected(struct bt_conn *conn, uint8_t reason)
{
    LOG_INF("Disconnected. Reason %d", reason);
    bt_conn_unref(my_conn);

	/* STEP 3.3  Turn the connection status LED off */
    dk_set_led(CONNECTION_STATUS_LED, 0);
}

/* STEP 2.1 - Declare the connection_callback structure */
struct bt_conn_cb connection_callbacks = {
    .connected              = on_connected,
    .disconnected           = on_disconnected,
};

[haakonsh]

I made a mistake, I forgot you are operating as the central and the process is a bit different. 

The connection instance object is set in the function 'bt_nus_handles_assign' in nrf\subsys\bluetooth\services\nus_client.c:168

	/* Assign connection instance. */
	nus_c->conn = bt_gatt_dm_conn_get(dm);

The GATT Discovery Manager is run after a connection has been established in order to read a connected peripheral's GATT services and characteristics. In the NUS client sample this library is used to identify whether the connected peripheral has a NUS service, and to store a given connection instance object if it does.