samples: bluetooth: central_uart: status LEDs for nRF54LM20 Dongle

samples/bluetooth/central_uart/CMakeLists.txt

@@ -11,5 +11,6 @@ project(central_uart)
 # NORDIC SDK APP START
 target_sources(app PRIVATE
   src/main.c
+  src/leds.c
 )
 # NORDIC SDK APP END

samples/bluetooth/central_uart/README.rst

@@ -50,6 +50,25 @@ When you plug the dongle into a USB port, the following interfaces are available
      - NUS
      - Nordic UART Service
 
+User interface
+**************
+
+.. tabs::
+
+   .. group-tab:: nRF54LM20 Dongle
+
+      Green LED:
+         Lit when connected over Bluetooth LE.
+         Blinks briefly when data is sent or received over Bluetooth LE.
+
+      Blue LED:
+         Blinks when debug messages are emitted.
+
+   .. group-tab:: Other supported boards
+
+      See the list of supported boards in :ref:`central_uart_requirements`.
+      No buttons and LEDs are used.
+
 .. _central_uart_debug:
 
 Debugging

samples/bluetooth/central_uart/boards/nrf54lm20dongle_nrf54lm20b_cpuapp.conf

@@ -15,3 +15,6 @@ CONFIG_UDC_DRIVER_LOG_LEVEL_WRN=y
 # The sample requires UART async API that is not supported by the USB CDC ACM UART driver yet.
 # Hence we need the UART async adapter as the intermediate layer.
 CONFIG_UART_ASYNC_ADAPTER=y
+
+# Indicate BLE traffic and log activity using LEDs.
+CONFIG_GPIO=y

samples/bluetooth/central_uart/boards/nrf54lm20dongle_nrf54lm20b_cpuapp.overlay

@@ -12,6 +12,8 @@
 / {
 	chosen {
 		zephyr,shell-uart = &nus_cdc_acm_uart;
+		nordic,central-uart-ble-led = &led0_green;
+		nordic,central-uart-log-led = &led0_blue;
 	};
 };
 

samples/bluetooth/central_uart/src/leds.c

@@ -0,0 +1,167 @@
+/*
+ * Copyright (c) 2026 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+#include "leds.h"
+
+#include <zephyr/device.h>
+#include <zephyr/devicetree.h>
+#include <zephyr/drivers/gpio.h>
+#include <zephyr/kernel.h>
+#include <zephyr/logging/log.h>
+#include <zephyr/logging/log_backend.h>
+#include <zephyr/logging/log_msg.h>
+#include <zephyr/sys/__assert.h>
+
+#define LED_BLINK_MS	50
+#define LED_BLINK_COUNT 10
+
+LOG_MODULE_DECLARE(central_uart);
+
+#if DT_HAS_CHOSEN(nordic_central_uart_ble_led)
+
+static const struct gpio_dt_spec ble_led =
+	GPIO_DT_SPEC_GET(DT_CHOSEN(nordic_central_uart_ble_led), gpios);
+static bool ble_connected;
+static uint8_t ble_led_blink_remaining;
+static void ble_led_blink_handler(struct k_timer *timer);
+static K_TIMER_DEFINE(ble_led_blink_timer, ble_led_blink_handler, NULL);
+
+static void ble_led_blink_handler(struct k_timer *timer)
+{
+	int rc;
+
+	if (ble_led_blink_remaining > 0) {
+		ble_led_blink_remaining--;
+		rc = gpio_pin_toggle_dt(&ble_led);
+	} else {
+		k_timer_stop(timer);
+		rc = gpio_pin_set_dt(&ble_led, 1);
+	}
+
+	__ASSERT_NO_MSG(rc == 0);
+}
+
+void leds_init(void)
+{
+	int rc;
+
+	if (!gpio_is_ready_dt(&ble_led)) {
+		LOG_WRN("BLE LED not ready");
+		return;
+	}
+
+	rc = gpio_pin_configure_dt(&ble_led, GPIO_OUTPUT_INACTIVE);
+	__ASSERT_NO_MSG(rc == 0);
+}
+
+void leds_set_ble_connected(bool connected)
+{
+	int rc;
+
+	if (!gpio_is_ready_dt(&ble_led)) {
+		return;
+	}
+
+	k_timer_stop(&ble_led_blink_timer);
+
+	ble_connected = connected;
+	rc = gpio_pin_set_dt(&ble_led, connected ? 1 : 0);
+	__ASSERT_NO_MSG(rc == 0);
+}
+
+void leds_indicate_ble_traffic(void)
+{
+	if (!gpio_is_ready_dt(&ble_led) || !ble_connected) {
+		return;
+	}
+
+	k_timer_stop(&ble_led_blink_timer);
+
+	ble_led_blink_remaining = LED_BLINK_COUNT;
+	k_timer_start(&ble_led_blink_timer, K_MSEC(LED_BLINK_MS), K_MSEC(LED_BLINK_MS));
+}
+
+#else
+
+void leds_init(void)
+{
+	/* LED not configured */
+}
+
+void leds_set_ble_connected(bool connected)
+{
+	/* LED not configured */
+
+	ARG_UNUSED(connected);
+}
+
+void leds_indicate_ble_traffic(void)
+{
+	/* LED not configured */
+}
+
+#endif /* DT_HAS_CHOSEN(nordic_central_uart_ble_led) */
+
+#if DT_HAS_CHOSEN(nordic_central_uart_log_led)
+
+/*
+ * Implement a dummy logging backend that blinks the log LED on log activity.
+ */
+static const struct gpio_dt_spec log_led =
+	GPIO_DT_SPEC_GET(DT_CHOSEN(nordic_central_uart_log_led), gpios);
+static uint8_t log_led_blink_remaining;
+static void log_led_blink_handler(struct k_timer *timer);
+static K_TIMER_DEFINE(log_led_blink_timer, log_led_blink_handler, NULL);
+
+static void log_led_blink_handler(struct k_timer *timer)
+{
+	int rc;
+
+	if (log_led_blink_remaining > 0) {
+		log_led_blink_remaining--;
+		rc = gpio_pin_toggle_dt(&log_led);
+	} else {
+		k_timer_stop(timer);
+		rc = gpio_pin_set_dt(&log_led, 0);
+	}
+
+	__ASSERT_NO_MSG(rc == 0);
+}
+
+static void log_backend_led_process(const struct log_backend *const backend,
+				    union log_msg_generic *msg)
+{
+	ARG_UNUSED(backend);
+	ARG_UNUSED(msg);
+
+	k_timer_stop(&log_led_blink_timer);
+
+	log_led_blink_remaining = LED_BLINK_COUNT;
+	k_timer_start(&log_led_blink_timer, K_NO_WAIT, K_MSEC(LED_BLINK_MS));
+}
+
+static void log_backend_led_init(const struct log_backend *const backend)
+{
+	int rc;
+
+	ARG_UNUSED(backend);
+
+	if (!gpio_is_ready_dt(&log_led)) {
+		LOG_WRN("Log LED not ready");
+		return;
+	}
+
+	rc = gpio_pin_configure_dt(&log_led, GPIO_OUTPUT_INACTIVE);
+	__ASSERT_NO_MSG(rc == 0);
+}
+
+static const struct log_backend_api log_backend_led_api = {
+	.process = log_backend_led_process,
+	.init = log_backend_led_init,
+};
+
+LOG_BACKEND_DEFINE(log_backend_led, log_backend_led_api, true);
+#endif /* DT_HAS_CHOSEN(nordic_central_uart_log_led) */

samples/bluetooth/central_uart/src/leds.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2026 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+#ifndef LEDS_H_
+#define LEDS_H_
+
+#include <stdbool.h>
+
+/**
+ * @brief Initialize status LEDs (if configured).
+ *
+ * The status LEDs may be enabled by setting the following devicetree chosen properties:
+ * - nordic,central-uart-ble-led: BLE activity LED
+ * - nordic,central-uart-log-led: Log activity LED
+ */
+void leds_init(void);
+
+/**
+ * @brief Drive BLE LED on when connected, off when disconnected.
+ */
+void leds_set_ble_connected(bool connected);
+
+/**
+ * @brief Indicate BLE traffic (RX or TX).
+ *
+ * While connected, briefly blinks the BLE LED to indicate traffic.
+ */
+void leds_indicate_ble_traffic(void);
+
+#endif /* LEDS_H_ */

samples/bluetooth/central_uart/src/main.c

@@ -34,6 +34,8 @@
 
 #include <zephyr/logging/log.h>
 
+#include "leds.h"
+
 #define LOG_MODULE_NAME central_uart
 LOG_MODULE_REGISTER(LOG_MODULE_NAME);
 
@@ -85,6 +87,8 @@ static void ble_data_sent(struct bt_nus_client *nus, uint8_t err,
 	ARG_UNUSED(data);
 	ARG_UNUSED(len);
 
+	leds_indicate_ble_traffic();
+
 	k_sem_give(&nus_write_sem);
 
 	if (err) {
@@ -99,6 +103,8 @@ static uint8_t ble_data_received(struct bt_nus_client *nus,
 
 	int err;
 
+	leds_indicate_ble_traffic();
+
 	for (uint16_t pos = 0; pos != len;) {
 		struct uart_data_t *tx = k_malloc(sizeof(*tx));
 
@@ -390,6 +396,8 @@ static void connected(struct bt_conn *conn, uint8_t conn_err)
 
 	LOG_INF("Connected: %s", addr);
 
+	leds_set_ble_connected(true);
+
 	static struct bt_gatt_exchange_params exchange_params;
 
 	exchange_params.func = exchange_func;
@@ -423,6 +431,7 @@ static void disconnected(struct bt_conn *conn, uint8_t reason)
 		return;
 	}
 
+	leds_set_ble_connected(false);
 	bt_conn_unref(default_conn);
 	default_conn = NULL;
 
@@ -624,6 +633,8 @@ int main(void)
 {
 	int err;
 
+	leds_init();
+
 	err = bt_conn_auth_cb_register(&conn_auth_callbacks);
 	if (err) {
 		LOG_ERR("Failed to register authorization callbacks.");