PIR sensor

Discussion in 'General Electronics Chat' started by ierah honey, Jun 30, 2015.

  1. ierah honey

    Thread Starter New Member

    Jun 30, 2015
    nothing with the old discussion,
    i would like to ask about pir sensor. i am doing a project where im using the sensor to detect motion and will automatically turn on the light and stay high unless there is no people in the room. and im using PIR sensor connected with arduino. the pir sensor seems to be LOW when the things in static condition. my problem is, how can we make its output always high? is it the problem with the coding or we can change its circuit or changing to another type of sensor ? thank you.
  2. Wendy


    Mar 24, 2008
    Welcome to AAC!

    A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own.

    In addition, you have practiced the arcane art of necromancy, the revival of a long dead thread. Likely the OP (Original Poster) has solved his problem in the years that has passed, or thrown it away, or something.

    This was split from PIR sensor
  3. ericgibbs

    Senior Member

    Jan 29, 2010
    The problem is that a 'persons' body IR radiation is close a to constant level, say a DC level.
    To enable the PIR to detector to sense the persons radiated IR, the signal has to be converted from say steady DC signal to an AC signal.

    This is achieved by the design of lens system covering the detector. If you look at the PIR lens its either a honeycomb pattern or a slotted pattern.

    So as the person is moving in front of the PIR, the lens system causes the IR signal falling on the sensor to change in intensity, ie: effectively an AC signal
    This AC signal is amplified and output as a voltage level.

    So basically the person must keep moving within the coverage of the PIR, if the sensor is to continue detecting him/her.
    Last edited: Jul 1, 2015