https://devzone.nordicsemi.com/f/nordic-q-a/42358/how-can-i-add-h-files-keil-projectHi folks, I want to some changes uart project. So i added nrf_drv_timer.c but i din&#39;t header file and i encountered 3 errors when i compile my project. Here is some screen shut. Finally i should say, i repeated that this link----&gt; https://devzoneen-USTelligent Community 13Thu, 10 Jan 2019 14:05:50 GMThttps://devzone.nordicsemi.com/thread/164946?ContentTypeID=1Thu, 10 Jan 2019 14:05:50 GMT137ad170-7792-4731-bb38-c0d22fbe4515:5b890ab2-50f4-4c5f-8527-26100be01ce2awneil<p>Glad that the issue is solved.</p> <p>Regarding the actual question in the thread Title, &quot;<strong>How Can I Add .h Files Keil Project</strong>&quot;, the&nbsp;answer is that there is no need to add <em>header</em> files to the Project.</p> <p>The compiler finds header files via the Include Paths setting, and the IDE then lists them in the project just for your information.</p> <p>See:&nbsp;<a href="http://www.keil.com/support/man/docs/uv4/uv4_dg_adscc.htm">http://www.keil.com/support/man/docs/uv4/uv4_dg_adscc.htm</a>&nbsp;- near the end of the page.</p> <p>(most) other IDEs are similar.</p> <p></p> <div class="author header thread-starter"> <div class="avatar"></div> </div><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/164924?ContentTypeID=1Thu, 10 Jan 2019 13:09:36 GMT137ad170-7792-4731-bb38-c0d22fbe4515:902a271e-82c1-4f5f-8ac9-9ae4cd0507carraa<p>I solved problem. It is about sdk_config.h.</p> <p>I reliazed when i check timer example,&nbsp;</p> <p>#ifndef TIMER_ENABLED<br />#define TIMER_ENABLED 1<br />#endif</p> <p>#ifndef TIMER1_ENABLED<br />#define TIMER1_ENABLED 1<br />#endif</p> <p>it must be 1 booth together. I missed it. When i change, it is work!</p><div style="clear:both;"></div>