This video is about a further improvements in the firmware of a PIC micro controller based frequency counter and crystal tester in kit form sold on the internet under many names, for example "1Hz-50MHz Digital LED DIY Kits Crystal Oscillator Frequency Counter Tester".<br /><br />This video came about while I played around measuring revolutions per minute (RPM) of various objects, like fans or propellers. <br /><br />In previous videos, I described modifying the hardware to change the horrible "crystal oscillator tester" part into a pre-amp for the counter and how to improve readout resolution in the Khz range. These videos are<br />Changing the hardware: <a href="https://youtu.be/0BxpMm6SLoE" target="_blank" rel="nofollow">https://youtu.be/0BxpMm6SLoE</a><br />Changing the firmware: <a href="https://youtu.be/8rOCmhPWLWw" target="_blank" rel="nofollow">https://youtu.be/8rOCmhPWLWw</a><br />Improving resulution and adding RPM mode: <a href="https://youtu.be/0D6EcgTQtNw" target="_blank" rel="nofollow">https://youtu.be/0D6EcgTQtNw</a><br /><br />The firmware (previous and latest version) as source or HEX file can be downloaded here:<br /><a href="https://github.com/TheHWcave/PIC-freq.counter-modification/" target="_blank" rel="nofollow">https://github.com/TheHWcave/PIC-freq.counter-modification/</a><br />...<br /><a href="https://www.youtube.com/watch?v=QlIv1DEAvQw" target="_blank" rel="nofollow">https://www.youtube.com/watch?v=QlIv1DEAvQw</a>