<div class="entry-content">
    <div class="jetpack-video-wrapper"><span class="embed-youtube" style="text-align:center; display: block;"><iframe src="https://www.youtube.com/embed/rMoTqSC9wrY" class="youtube-player" width="740" height="416.418" frameborder="0" allowfullscreen></iframe></span>
    </div>
    <div class="blog-content">
In this tutorial you will design and build your own keyboard. You will also learn all the essentials to design and build any electronics. Enjoy!
    </div>
    
    <div class="blog-content-links">
        <div>
            Links:
        </div>
        <ul class="links-list">
            <li class="links-list-item"><a href="https://github.com/FEDEVEL/custom-keyboard">Github (HW + 3D + SW)</a></li>
            <li class="links-list-item"><a href="https://fedevel.com/courses">FEDEVEL Online courses</a></li>
        </ul>
    </div>  
</div>

Tutorial - Custom DIY Keyboard Design and Build | Part 2: Keyboard Schematic

<div class="entry-content">
    <div class="jetpack-video-wrapper"><span class="embed-youtube" style="text-align:center; display: block;"><iframe src="https://www.youtube.com/embed/N4cLFE0FF2U" class="youtube-player" width="740" height="416.418" frameborder="0" allowfullscreen></iframe></span>
    </div>
    <div class="blog-content">
        In this tutorial you will design and build your own keyboard. You will also learn all the essentials to design and build any electronics. Enjoy!
    </div>

    <div class="blog-content-chapters">
        <div>
            Chapters:
        </div>
        <ul class="chapters-list">
            <li class="chapters-list-item"><span class="chapters-time">00:00</span><span class="chapters-text">What is this tutorial about</span></li>
            <li class="chapters-list-item"><span class="chapters-time">03:34</span><span class="chapters-text">Starting a new project</span></li>
            <li class="chapters-list-item"><span class="chapters-time">08:42</span><span class="chapters-text">Adding RP2040</span></li>
            <li class="chapters-list-item"><span class="chapters-time">14:43</span><span class="chapters-text">Adding 100nF</span></li>
            <li class="chapters-list-item"><span class="chapters-time">20:12</span><span class="chapters-text">Adding 2.2uF</span></li>
            <li class="chapters-list-item"><span class="chapters-time">23:14</span><span class="chapters-text">Adding 200R</span></li>
            <li class="chapters-list-item"><span class="chapters-time">25:43</span><span class="chapters-text">Adding 27R</span></li>
            <li class="chapters-list-item"><span class="chapters-time">27:40</span><span class="chapters-text">Adding USB-C connector</span></li>
            <li class="chapters-list-item"><span class="chapters-time">31:25</span><span class="chapters-text">Adding ESD protection</span></li>
            <li class="chapters-list-item"><span class="chapters-time">34:03</span><span class="chapters-text">Adding 1uF</span></li>
            <li class="chapters-list-item"><span class="chapters-time">36:10</span><span class="chapters-text">Connecting USB CC pins</span></li>
            <li class="chapters-list-item"><span class="chapters-time">36:46</span><span class="chapters-text">Adding 5.1k</span></li>
            <li class="chapters-list-item"><span class="chapters-time">38:21</span><span class="chapters-text">Voltage regulator 5V to 3V3</span></li>
            <li class="chapters-list-item"><span class="chapters-time">42:27</span><span class="chapters-text">Adding 47uF</span></li>
            <li class="chapters-list-item"><span class="chapters-time">45:49</span><span class="chapters-text">Crystal ABM8-272-T3</span></li>
            <li class="chapters-list-item"><span class="chapters-time">47:22</span><span class="chapters-text">Adding 1k</span></li>
            <li class="chapters-list-item"><span class="chapters-time">48:32</span><span class="chapters-text">Adding 15pF</span></li>
            <li class="chapters-list-item"><span class="chapters-time">49:48</span><span class="chapters-text">Adding 1M</span></li>
            <li class="chapters-list-item"><span class="chapters-time">52:52</span><span class="chapters-text">Flash W25Q128JVS</span></li>
            <li class="chapters-list-item"><span class="chapters-time">58:20</span><span class="chapters-text">Boot Select Button</span></li>
            <li class="chapters-list-item"><span class="chapters-time">1:01:09</span><span class="chapters-text">Adding 100k</span></li>
            <li class="chapters-list-item"><span class="chapters-time">1:03:10</span><span class="chapters-text">Reset Button</span></li>
            <li class="chapters-list-item"><span class="chapters-time">1:04:28</span><span class="chapters-text">Adding 10k</span></li>
            <li class="chapters-list-item"><span class="chapters-time">1:08:23</span><span class="chapters-text">Adding 1x3 Header</span></li>
            <li class="chapters-list-item"><span class="chapters-time">1:11:50</span><span class="chapters-text">User LED</span></li>
            <li class="chapters-list-item"><span class="chapters-time">1:15:06</span><span class="chapters-text">Power LED</span></li>
            <li class="chapters-list-item"><span class="chapters-time">1:16:38</span><span class="chapters-text">Thank you for watching</span></li>
    </div>
    
    <div class="blog-content-links">
        <div>
            Links:
        </div>
        <ul class="links-list">
            <li class="links-list-item"><a href="https://oshwlab.com/robertferanec/custom-keyboard">Finished project (EasyEDA)</a></li>
            <li class="links-list-item"><a href="https://github.com/FEDEVEL/custom-keyboard">Github (HW + 3D + SW)</a></li>
            <li class="links-list-item"><a href="https://www.thingiverse.com/thing:6784228">Thingiverse (3D)</a></li>
            <li class="links-list-item"><a href="https://www.youtube.com/playlist?list=PLXvLToQzgzdftro2qK5In8p6ExsDFdpzw">Link to the complete playlist</a></li>
            <li class="links-list-item"><a href="https://fedevel.com/courses">FEDEVEL Online courses</a></li>
        </ul>
    </div>  
</div>

Tutorial - Custom DIY Keyboard Design and Build: Schematic + PCB + Case | Part 1 - RP2040

<div class="entry-content">
    <div class="jetpack-video-wrapper"><span class="embed-youtube" style="text-align:center; display: block;"><iframe src="https://www.youtube.com/embed/Lqc1jmbSxnE" class="youtube-player" width="740" height="416.418" frameborder="0" allowfullscreen></iframe></span>
    </div>
    <div class="blog-content">
Why is the thickness of PCB layers important? Explained.
    </div>

    <div class="blog-content-chapters">
        <div>
            Chapters:
        </div>
        <ul class="chapters-list">
            <li class="chapters-list-item"><span class="chapters-time">00:00</span><span class="chapters-text">What is this video about</span></li>
            <li class="chapters-list-item"><span class="chapters-time">00:36</span><span class="chapters-text">What is PCB stackup</span></li>
            <li class="chapters-list-item"><span class="chapters-time">01:08</span><span class="chapters-text">Is stackup important?</span></li>
            <li class="chapters-list-item"><span class="chapters-time">01:37</span><span class="chapters-text">Layer thickness vs. crosstalk</span></li>
            <li class="chapters-list-item"><span class="chapters-time">03:37</span><span class="chapters-text">Layer thickness vs. track width</span></li>
            <li class="chapters-list-item"><span class="chapters-time">05:11</span><span class="chapters-text">Layer count and order</span></li>
            <li class="chapters-list-item"><span class="chapters-time">07:44</span><span class="chapters-text">Conclusion</span></li>
    </div>
    
    <div class="blog-content-links">
        <div>
            Links:
        </div>
        <ul class="links-list">
            <li class="links-list-item"><a href="https://fedevel.com/courses">FEDEVEL Online courses</a></li>
        </ul>
    </div>  
</div>

How to choose PCB?

<div class="entry-content">
    <div class="blog-content-img-wrapper">
        <img src="https://assets.fedevel.com/blog/2019/10/ac6c6-running-memory-tests.jpg" alt="running memory tests" />
    </div>
    <div class="blog-content">
        Every hardware design engineer wants to be sure that the DDR3 memory interface is working correctly. Here are some real examples of DDR3 memory testing from our open source <a href="http://www.imx6rex.com/">iMX6 Rex project</a>.
    </div>
    <div class="blog-content">
        <h2 class="blog-content-heading">Which of the memory tests?</h2>
        There are a lot of memory tests available. For this project I used three:
        <ul class="content-list">
            <li class="content-list-item"><span class="content-text">the standard ubuntu <a href="http://manpages.ubuntu.com/manpages/hardy/man8/memtester.8.html">memtester</a></span></li>
            <li class="content-list-item"><span class="content-text"><a href="https://code.google.com/p/stressapptest/">stressapptest</a> (according to the website “… It has been used at Google for some time …”)</span></li>
            <li class="content-list-item"><span class="content-text">the Freescale memory test included in the <a href="https://community.freescale.com/docs/DOC-96412">i.MX6 DDR Stress Test Tool</a> (the same tool which is used also for calibration)</span></li>
        </ul><br>
        I recommend the stressapptest.
    </div>
    
    <div class="blog-content">
        <h2 class="blog-content-heading">What did I test?</h2>
        I was curious, so I have done tests of “uncalibrated” and “calibrated” board. “Uncalibrated” board was using the unchanged settings of DDR3 memory registers (the same values as used on the reference board), “calibrated” board was using the proper register values which I have got after the DDR3 calibration.
    </div>

    <div class="blog-content">
        <h2 class="blog-content-heading">The results</h2>
        Initially, I was running the “uncalibrated” board. The <b>memtester</b> software was running on this board for a week with <b>no errors.</b> When I used the <b>stressapptest</b> – the board always <b>failed within one hour</b>. This is how the failing looked: <br><br>

        <i>“Uncalibrated DDR3” – Examples of failing memory test</i>
    </div>
    <div class="blog-content-code">
        <code>Log: Seconds remaining: 4350<br>
        Report Error: miscompare : DIMM Unknown : 1 : 1658s<br>
        Hardware Error: miscompare on CPU 0(0xF) at 0x2be72978(0x4ca1997a:DIMM Unknown): read:0xff7fffffffffffff, reread:0xff7fffffffffffff expected:0xff7fffffff7fffff<br><br>
        
        Log: Seconds remaining: 4840<br>
        Report Error: miscompare : DIMM Unknown : 1 : 1169s<br>
        Hardware Error: miscompare on CPU 0(0xF) at 0x2bd89a78(0x4e3c7a7a:DIMM Unknown): read:0xff7fffffffffffff, reread:0xff7fffffffffffff expected:0xff7fffffff7fffff<br><br>
          
        Log: Seconds remaining: 3100<br>
        Report Error: miscompare : DIMM Unknown : 1 : 2904s<br>
        Hardware Error: miscompare on CPU 0(0xF) at 0x38171e78(0x27dcbe7a:DIMM Unknown): read:0xff7fffffffffffff, reread:0xff7fffffffffffff expected:0xff7fffffff7fffff<br><br>
        
        Log: Seconds remaining: 5550<br>
        Report Error: miscompare : DIMM Unknown : 1 : 455s<br>
        Hardware Error: miscompare on CPU 0(0xF) at 0x2fced578(0x200f157a:DIMM Unknown): read:0xff7fffffffffffff, reread:0xff7fffffffffffff expected:0xff7fffffff7fffff</code>
    </div> 
    <div class="blog-content-text">
        After applying the correct DDR3 settings from the DDR3 calibration (adding the correct register settings into uBoot), the same board was running perfectly.<br><br>

        <i>“Calibrated DDR3” – running perfectly over night (the same board was failing before)</i>
    </div>
    <div class="blog-content-code">
        <code>Stats: Found 0 hardware incidents<br>
        Stats: Completed: 32146856.00M in 0.00s infMB/s, with 0 hardware incidents, 0 errors<br>
        Stats: Memory Copy: 32146856.00M at -24559.40MB/s<br>
        Stats: File Copy: 0.00M at 0.00MB/s<br>
        Stats: Net Copy: 0.00M at 0.00MB/s<br>
        Stats: Data Check: 0.00M at 0.00MB/s<br>
        Stats: Invert Data: 0.00M at 0.00MB/s<br> Stats: Disk: 0.00M at 0.00MB/s<br><br>
        
        Status: PASS - please verify no corrected errors</code>
    </div> 
    <div class="blog-content-text">
        Here is the command line I used for the basic testing:
    </div>
    <div class="blog-content-code">
        <code># stressapptest -s 3600 -M 256 -m 4 -C 4 -W</code>
    </div> 
    <div class="blog-content-text">
        If you would like to install the strassapptest on your own ARM board, <a href="http://www.imx6rex.com/software/stress-testing-stressapptest/">check out here.</a>
    </div>

    <div class="blog-content">
        <h2 class="blog-content-heading">Be aware</h2>
        Be aware, that you need to test more boards. I have tested couple of “uncalibrated” boards and not all of them failed the stressapptest. When you are happy with the results (all your boards must always pass the test), take couple of boards (at least 5) and run the same tests in an environmental chamber (from -40C up to the maximum temperature … 60/70/80C ..). All the “calibrated” boards must pass your testing.<br><br>

        Happy testing!
    </div>
    
    <div class="blog-content-links">
        <div>
            Links:
        </div>
        <ul class="links-list">
            <li class="links-list-item"><a href="http://www.imx6rex.com/">iMX6 Rex project</a></li>
            <li class="links-list-item"><a href="http://manpages.ubuntu.com/manpages/hardy/man8/memtester.8.html">Memtester</a></li>
            <li class="links-list-item"><a href="https://code.google.com/p/stressapptest/">Stressapptest</a></li>
            <li class="links-list-item"><a href="https://community.freescale.com/docs/DOC-96412">i.MX6 DDR Stress Test Tool</a></li>
            <li class="links-list-item"><a href="http://www.imx6rex.com/software/stress-testing-stressapptest/">iMX6 Rex - Stress tests</a></li>
        </ul>
    </div>
</div>


ARM DDR3 Memory testing

<div class="entry-content">
    <div class="blog-content-img-wrapper">
        <img src="https://assets.fedevel.com/blog/2019/10/4bf6f-imx6-rex-infra-red-comparision-image.jpg" alt="iMX6 Rex Infra-red comparision image" />
    </div>
    <div class="blog-content">
        Here are some pictures of the same PCB, but running different software applications:
        <ul class="content-list">
            <li class="content-list-item"><span class="content-text">Notice the CPU temperature difference when nothing is running (49.9°C) and when a test is running (76.4) – compare the first and third picture.</span></li>
            <li class="content-list-item"><span class="content-text">Have a look at the picture in the middle. Memories become more visible when running a memory test.</span></li>
            <li class="content-list-item"><span class="content-text">See the huge difference in Ethernet temperature when Ethernet cable is connected (the middle picture, bottom right corner) and disconnected.</span></li>
            <li class="content-list-item"><span class="content-text">It’s interesting to see, how the whole PCB will warm up from a few hot components – the module PCB is much warmer than the Baseboard PCB (in background).</span></li>
        </ul>
    </div>

    <div class="blog-content-text">
        <i>Picture: Uboot only (Ethernet unplugged).</i>
    </div>
    <div class="blog-content-img-wrapper">
        <img src="https://assets.fedevel.com/blog/2019/10/05f18-01-uboot-without-eth-module.jpg" alt="01 uboot without eth module" />
    </div>

    <div class="blog-content-text">
        <i>Picture: Memory test (Ethernet connected)</i>
    </div>
    <div class="blog-content-img-wrapper">
        <img src="https://assets.fedevel.com/blog/2019/10/f9e30-03-stresstest-mem-module.jpg" alt="03 stresstest mem module" />
    </div>

    <div class="blog-content-text">
        <i>Picture: CPU test + Memory test (Ethernet unplugged)</i>
    </div>
    <div class="blog-content-img-wrapper">
        <img src="https://assets.fedevel.com/blog/2019/10/32526-05-stresstest-cpumem-eth-unplugged-module.jpg" alt="05 stresstest cpu+mem eth unplugged module" />
    </div>

    <div class="blog-content">
        <h2 class="blog-content-heading">If you use a hot air gun, how the heat will spread on PCB?</h2>
        This was also an interesting experiment, we used a hot air gun (you can see it on the right picture) to heat up a small PCB. Notice, how the middle GND exposed pad is much colder then the area without copper <i>(note: the result may be affected by the shiny surface of golden areas).</i>
    </div>

    <div class="blog-content-img-wrapper">
        <img src="https://assets.fedevel.com/blog/2019/10/30c3e-sps-bottom-gun-rear1-180c2b0c-comparision.jpg" alt="SPS bottom gun rear1 180°C comparision" />
    </div>
</div>

A different look at your PCB – Infrared

<div class="entry-content">
    <div class="jetpack-video-wrapper"><span class="embed-youtube" style="text-align:center; display: block;"><iframe src="https://www.youtube.com/embed/67WhV0EDqCA" class="youtube-player" width="740" height="416.418" frameborder="0" allowfullscreen></iframe></span>
    </div>
    <div class="blog-content">
        This video will show you how the layers of a multi-layer PCB are put together. Thank you very much to our PCB manufacturer SQP International, where I could make this video.
    </div>
    <div class="blog-content-chapters">
        <div>
            Chapters:
        </div>
        <ul class="chapters-list">
            <li class="chapters-list-item">
                <span class="chapters-time">00:00</span><span class="chapters-text">Intro</span>
            </li>
            <li class="chapters-list-item">
                <span class="chapters-time">00:15</span><span class="chapters-text">Ingredients</span>
            </li>
            <li class="chapters-list-item">
                <span class="chapters-time">05:25</span><span class="chapters-text">Techniques</span>
            </li>
            <li class="chapters-list-item">
                <span class="chapters-time">06:11</span><span class="chapters-text">Plating</span>
            </li>
            <li class="chapters-list-item">
                <span class="chapters-time">08:09</span><span class="chapters-text">Drilling</span>
            </li>
        </ul>
    </div> 
    <div class="blog-content-links">
        <div>
            Links:
        </div>
        <ul class="links-list">
            <li class="links-list-item"><a href="http://www.PCBone.com/">PCB manufacturer SQP International</a></li>
        </ul>
    </div> 
</div>


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