,maybe this one works?

Dependencies:   BLE_API mbed nRF51822

Revision:
0:7a9eb6b6ae60
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ButtonService.h	Sun Oct 28 12:15:46 2018 +0000
@@ -0,0 +1,42 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2006-2013 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __BLE_BUTTON_SERVICE_H__
+#define __BLE_BUTTON_SERVICE_H__
+
+class ButtonService {
+public:
+    const static uint16_t BUTTON_SERVICE_UUID              = 0xA000;
+    const static uint16_t BUTTON_STATE_CHARACTERISTIC_UUID = 0xA001;
+
+    ButtonService(BLE &_ble, bool buttonPressedInitial) :
+        ble(_ble), buttonState(BUTTON_STATE_CHARACTERISTIC_UUID, &buttonPressedInitial, GattCharacteristic::BLE_GATT_CHAR_PROPERTIES_NOTIFY)
+    {
+        GattCharacteristic *charTable[] = {&buttonState};
+        GattService         buttonService(ButtonService::BUTTON_SERVICE_UUID, charTable, sizeof(charTable) / sizeof(GattCharacteristic *));
+        ble.gattServer().addService(buttonService);
+    }
+
+    void updateButtonState(bool newState) {
+        ble.gattServer().write(buttonState.getValueHandle(), (uint8_t *)&newState, sizeof(bool));
+    }
+
+private:
+    BLE                              &ble;
+    ReadOnlyGattCharacteristic<bool>  buttonState;
+};
+
+#endif /* #ifndef __BLE_BUTTON_SERVICE_H__ */