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I fixed the pir sensor on the top of servo motor.while the servo motor's rotation the pir was also rotated by servo motor's motion.but the problem I had founded that pir sensor had always indicated motion of human which I realized through a buzzer. When I take of the sensor from servo motor it had worked as well. So my question is that can we use pir sensor while it's moving?

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    \$\begingroup\$ As Einstein already noticed: movement is relative to the observant. There is nothing which can make a PIR sensor differ between a moving object and it's own movement. All you can do is ignore the signals from it whilst you are moving it. \$\endgroup\$ – Oldfart Mar 22 '20 at 8:17
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A PIR sensor on its own is effectively just two Infrared sensors next to each other:

https://www.makerguides.com/hc-sr501-arduino-tutorial/

I assume you are using one with a fresnel lens on it, and a driver/detection circuit already built in. If so, it will be basically impossible to use it while moving, since it relies on detecting a change in temperature between two areas, and it will be detecting this constantly. They are meant for detecting motion, and you are moving all the time.

Even if you created your own driver, I imagine it would still be pretty difficult to do it (maybe impossible).

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    \$\begingroup\$ Where did you get this image from? \$\endgroup\$ – Bruce Abbott Mar 22 '20 at 8:21
  • \$\begingroup\$ Oops, added source to description \$\endgroup\$ – BeB00 Mar 22 '20 at 8:24
  • \$\begingroup\$ The credit doesn't show up in Chrome. I always add them as hyperlinks in the image caption. I think you've misinterpreted the drawing a little. There's only one PIR sensor. The Fresnel (capital for proper name) lens creates zones of sensitivity and only two are shown in the diagram. The artist should probably have made the output signal repeat as the person walks through the second sensing zone. \$\endgroup\$ – Transistor Mar 22 '20 at 8:43
  • \$\begingroup\$ @Transistor So initially I thought I was right, then I thought I was wrong, but it turns out I am actually right :P. PIR sensors do typically have two sensing elements in them, arranged back to back, which is why you get a positive signal and then a negative signal. As I initially said, a fresnel lens on its own would actually act in the way shown in that picture. A PIR lens is multiple fresnel lenses on a curved surface, creating multiple 2-sensor zones. In the picture is just one zone, but the answer to OPs question is the same regardless of whether they have a multi zone lens or not. \$\endgroup\$ – BeB00 Mar 22 '20 at 8:54
  • \$\begingroup\$ Thanks, BeB00. (I wasn't arguing about the relevance to the OP's question which you have answered correctly.) I assumed that the positive / negative pulses in the drawing were the differential signal of passing through one of the lens zones. I'm familiar with the lenses - both striped (outdoor type) and dimpled (ceiling type) ... \$\endgroup\$ – Transistor Mar 22 '20 at 9:15
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To supplement @BeB00's answer:

The illustrations in the linked MakerGuides article is not quite correct.

enter image description here

Figure 1. Modified sensing diagram. A pair of side-by-side PIR sensors in reverse-series connection sense motion while giving high immunity to changes background radiation due to temperature changes.

Here it becomes clear that due to the reverse-series connection that walking into the purple detection zone would generate a positive going pulse and walking into the orange zone would give a negative going pulse.

enter image description here

Figure 2. The type of Fresnel lens shown in the accompanying article.

The type of Fresnel lens shown in the article is used in lighthouse and theater lamps to give high aperture with short focal length. This is not what is required for a PIR motion sensor.

enter image description here

Figure 3. A top view of a typical PIR motion sensor lens.

As shown in Figure 3, the lens used in a PIR motion sensor is not what is commonly known as a Fresnel lens. Instead, it is designed as an array of cylindrical or spherical lenses to give a pattern of weak and strong sensing zones.

So my question is that can we use PIR sensor while it's moving?

Probably not. You would need to stop the motion for long enough to take a reading and check for motion over a specified time period.

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  • \$\begingroup\$ My understanding is that fresnel refers to the technique used to make the lens flat (in this spherical case, coencentric rings) as opposed to curved (this may not be the original meaning, but I think that is common usage now). All the PIR sensors I've seen do use this type of lens, but with multiple centres creating multiple "beams" \$\endgroup\$ – BeB00 Mar 23 '20 at 2:43

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