https://devzone.nordicsemi.com/f/nordic-q-a/22789/why-is-ble_cus-c-not-a-header-fileIn this tutorial github.com/.../custom_ble_service_example There are two additional files added to the template project ble_cus.c ble_cus.h I understand that ble_cus.h must be included as a header in both ble_cus.c and main.c Howeveren-USTelligent Community 13Thu, 15 Jun 2017 07:31:59 GMThttps://devzone.nordicsemi.com/thread/89601?ContentTypeID=1Thu, 15 Jun 2017 07:31:59 GMT137ad170-7792-4731-bb38-c0d22fbe4515:354bdc52-5e01-4025-92b1-cf8a8108561eJ&#248;rgen Holmefjord<p>Hi,</p> <p>You should not include source files the same way you include header files. The header files provide the declaration of variables and functions to your main application, while the source code should contain implementation of functions. Source files are included in the project and is compiled separately into object files. The object files are then linked into the complete application, together with main.</p> <p>In Keil, you add source files by right clicking the group you want to the file to, for instance <em>nRF_BLE_Services</em>, and click &quot;Add Existing Files to Group &#39;...&#39;&quot;.</p> <p>Best regards,</p> <p>Jørgen</p><div style="clear:both;"></div>