The PIR sold at Adafruit has a few adjustable components: retriggering, time and sensitivity.
No idea. Even the Adafruit page is cryptic about what this setting does…
The sensitivity potentiometer can’t really be quantified, but it reacts intuitively. The higher the potentiometer, the more sensitive the sensor will be. Adjust depending on your application. I have mine cranked to 11 ;-)
The time potentiometer sets the amount of time the sensor will stay “ON” after a trigger by mouvement. This is designed to go from 2.5 seconds to 4 minutes, but my PIR can only go as low as 6 seconds.
I have previously implied that there was a frequency adjustment possible on the PIR, but that is not exactly the case. You can adjust the length of time the trigger stays ON (as explained above), and you can adjust the length of time the trigged will stay OFF after that but for this you need to change a resistor that is soldered on the sensor’s board.