Yongsup Park has created a high-speed Teensy-based pulse counter with reliability down to a pulse width of 20ns or less — performance which typically requires equipment costing hundreds, or even thousands of dollars.

Using the FreqCount function, Yongsup iteratively reduced the pulse width until behavior became erratic. The Teensy 4.1’s 600MHz clock gives a theoretical resolution of 1.67ns, and was observed counting as little as 9ns pulse widths at 50MHz. The Rigol DG912 Pro waveform generator being used to test it has a rise/fall of 3ns, so reducing further would have been hard to measure anyway.

The pulse counter is part of a larger data acquisition app that runs in the browser without the need for a computer, using a Teensy 4.1 as a web server, USB device controller, and pulse counter. Testing results, code, and more can be found in the original forum thread.