ble_nus.c
BLE is the nRF52840's reason to exist: this sketch advertises a name, exposes the Nordic UART Service and pushes text frames to the nRF Connect app. The starting template of any low-power connected object.
Hardware
An nRF52840-MDK board (Nordic nRF52840, Cortex-M4F @ 64 MHz, 1 MB flash / 256 KB RAM, BLE 5 + 802.15.4) with onboard debugger, programmed in C with nRF5 SDK v17 and the S140 SoftDevice. nRF52840-MDK + a phone with the free nRF Connect app (Android/iOS).
Wiring
No wiring: the radio is onboard, the MDK carries a ceramic antenna.
How it works
The S140 SoftDevice owns the link layer; the advert carries name + service data, NUS adds RX/TX characteristics, ble_nus_string_send notifies the connected client.
Running it
Open the matching nRF5 SDK v17 example (custom_board target), paste this code into main.c, build with Segger Embedded Studio or the gcc Makefile, then flash through the onboard debugger.
Variants
Move to connectable + pairing, add the Battery Service (SAADC reading), or extend range with the Coded PHY (long-range BLE).
ble_nus.c
// nRF52840-MDK : peripheral BLE avec Nordic UART Service (NUS) sous SoftDevice S140.
// L'app "nRF Connect" voit "MDK-Capteur" et reçoit les notifications.
#include "nrf_sdh.h"
#include "nrf_sdh_ble.h"
#include "ble_advdata.h"
#include "nrf_ble_gatt.h"
#include "ble_nus.h"
#include "app_timer.h"
#define MANIFEST "MDK-Capteur"
NRF_BLE_GATT_DEF(m_gatt);
BLE_NUS_DEF(m_nus, NRF_SDH_BLE_TOTAL_LINK_COUNT);
static uint8_t trame[] = "t=21.5C";
static void conn_handle(ble_evt_t const *p, void *ctx) {
switch (p->header.evt_id) {
case BLE_GAP_EVT_CONNECTED: // un client est connecté
break;
case BLE_GAP_EVT_DISCONNECTED:
(void)ble_advertising_start(); // reprendre la publicité
break;
}
}
int main(void) {
nrf_sdh_enable_request();
app_timer_init();
uint32_t ram = nrf_sdh_ble_default_cfg_set(1, NULL);
nrf_sdh_ble_enable(&ram);
nrf_ble_gatt_init(&m_gatt, NULL);
ble_nus_init(&m_nus, NULL);
ble_radio_notification_init(3, 0, NULL, false);
ble_advdata_t adv = { .name_type = BLE_ADV_DATA_NAME_COMPLETE,
.p_name = MANIFEST };
ble_advdata_service_data_t sd = { .service_uuid = BLE_NUS_UUID,
.data = { .p_data = trame,
.size = sizeof(trame) - 1 } };
adv.p_service_data = &sd; adv.service_count = 1;
ble_advertising_start(BLE_ADV_MODE_FAST);
for (;;) {
app_sleep(); // le SoftDevice gère les connexions
ble_nus_string_send(&m_nus, trame, sizeof(trame) - 1);
}
}