I have an IR sensor that has an output pin that goes low when you put your hand over the sensor. I have a motor that I would like to turn on when you put your hand over the sensor. Currently I am using a mosfet to do that but the motor keeps running while my hand is over the sensor. This is not what I want. I want the motor to turn only for few seconds after the sensor is triggered, meaning I want the falling edge of the output signal to be a trigger. I do not want to do it with microcontroller. How do I do it. Thanks!!

 

Welcome to AAC!

How do I do it.

You could use a 555 timer.

From your description, it sounds like the sensor output remains low while it's blocked. In that case, you'd need to AC couple the trigger to the timer.

 

A resistor and a capacitor may do what you want.

Post a schematic of your circuit.

 

it may turn out to be not a reliable method to trigger anything as the iR backround may vary -- such as the reflections from moving doors , men animal bugs (fly sitting next to sensor and blinking eyes ... actually they can't do such ... well cleaning it's head . . . they always crawl up where they shouldn't ...) . . . room/outside light change