https://devzone.nordicsemi.com/f/nordic-q-a/5244/question-about-nrf51-dk-board-led-problem-not-blinkHello, I&#39;ve started bluetooth development with nRF51 DK since yesterday. My devlopment platform is KEIL-MDK(v5) Yesterday, I just tested my board, download the blink example and check the LED1 is blinking which period is 0.5sec. Today, I trieden-USTelligent Community 13Thu, 22 Jan 2015 04:15:23 GMThttps://devzone.nordicsemi.com/thread/18369?ContentTypeID=1Thu, 22 Jan 2015 04:15:23 GMT137ad170-7792-4731-bb38-c0d22fbe4515:388303b1-85a0-4dfa-abb9-517886e3f868Nguyen Hoan Hoang<p>The softdevice (S110, S120, ...) is required to run BLE app. You need to flash it in first. There is a hex file that comes with it. Download it form nordicsemi.com.</p><div style="clear:both;"></div>