Cheap frequency counter kit "1Hz-50MHz Digital LED DIY Kits Crystal Oscillator Frequency Counter Tester"

original design

https://www.qsl.net/dl4yhf/freq_counter/freq_counter.html

modifications

• A PIC based frequency counter kit - part 1:building and modifying https://www.youtube.com/watch?v=0BxpMm6SLoE
• A PIC based frequency counter kit - part 2:changing the firmware https://www.youtube.com/watch?v=8rOCmhPWLWw
• Frequency Counter Kit revisited: higher resolution and RPM mode https://www.youtube.com/watch?v=0D6EcgTQtNw&t=313s