How can I make a motor stop when the output of a PIR sensor is below a threshold?
Here is an outline of one of the ways of meeting the requirement. The motor can be connected through the contact leads of the relay.







simulate this circuit &ndash; Schematic created using CircuitLab

As the question does not indicate a specific problem arrived at after due research, this schematic is merely a pointer to start off a direction of study. Do not take any component values or choices as final.