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I was going through the data sheet of the PIR motion sensor when i saw this:a labeled PIR motion sensor

So what i couldn't understand was the H and L trigger and how to change from H to L or L to H (like to do we have to provide HIGH to the H trigger to activate it or something else). I found a little bit of description here but i'm not fully able to grasp this:

a table showing what H and L triggers are

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  • \$\begingroup\$ This seems to be a jumper. So you can remove it and place it in the other position. \$\endgroup\$ Dec 30, 2015 at 19:13

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If you move the jumper to L position the sensor will 'toggle' (change state) every time motion is detected - probably providing the on-board timer has timed out. This is unlikely to be of much use in a practical application. (Watch the comments for corrections!)

Moving the jumper to the H position will result in the more usual sensor logic. The sensor will turn on when motion is detected and turn off some time after the last motion is detected. This sensor will reset the timer (which would otherwise turn the output off) every time motion is detected and would be suitable, for example, for room occupancy lighting control where you don't want the lights to blink off while the unit resets.

Select the mode you want using the jumper and connect the output of the module (and ground and power) to your other circuitry to use the detector.

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  • \$\begingroup\$ I don't read 'L' as 'toggling' (i.e. changing state back and forth, with each change of state corresponding to an input event). I read it as 'pulsing' or 'triggering' for a short period with each event, i.e. event0 -> high...low, event1 -> high...low, event2 -> high...low, and not event0 -> high, event1 -> low, event2 -> high, etc. Small point. Otherwise your answer seems complete, accurate, and what was asked for. Perfect :-) \$\endgroup\$
    – gbulmer
    Dec 31, 2015 at 0:17
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It uses a 3 pin header with a jumper. The middle pin is common, going to the IC pin to set the mode you select. When the jumper is on pins 1 (top) and 2 the common pin is pulled high. When it's on 2 and 3 (Bottom), it's pulled low. You don't need to inject power or anything. You just move the jumper/shunt (the yellow block). See this:

enter image description here

As to how the sensor works in that mode, from https://learn.adafruit.com/pir-passive-infrared-proximity-motion-sensor/testing-a-pir:

Normal Mode: enter image description here

Retrigger Mode: enter image description here

Once you have the LED blinking, look on the back of the PIR sensor and make sure that the jumper is placed in the L position as shown below.

Now set up the testing board again. You may notice that when connecting up the PIR sensor as above, the LED does not stay on when moving in front of it but actually turns on and off every second or so. That is called "non-retriggering".

Now change the jumper so that it is in the H position. If you set up the test, you will notice that now the LED does stay on the entire time that something is moving. That is called "retriggering"

For most applications, "retriggering" (jumper in H position) mode is a little nicer. If you need to connect the sensor to something edge-triggered, you'll want to set it to "non-retriggering" (jumper in L position).

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  • \$\begingroup\$ Whats the difference between 1-2 jumped and 2-3 jumped? \$\endgroup\$ Dec 30, 2015 at 19:07
  • \$\begingroup\$ @Newbie_Programmer When the jumper is on pins 1 (top) and 2 the common pin is pulled high. When it's on 2 and 3 (Bottom), it's pulled low. \$\endgroup\$
    – Passerby
    Dec 30, 2015 at 19:08
  • \$\begingroup\$ What i meant is what happens to the PIR sensor when its pulled high or low \$\endgroup\$ Dec 30, 2015 at 19:10
  • \$\begingroup\$ @Newbie_Programmer exactly what it says in the data sheet table you posted. When the jumper is set high, it's in retrigger mode, the output pin will stay high/on as long as motion is sensed. When the jumper is set low, In Normal mode, the output pin will toggle on and off when motion is sensed. \$\endgroup\$
    – Passerby
    Dec 30, 2015 at 19:14

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