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Pir Sensor (human Targeting)

Discussion in 'Robotics & Mechatronics' started by johnjohn, Nov 30, 2007.

  1. johnjohn

    johnjohn New Member

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    I have been working on a robot using ultrasonic range detectors to patrol around my house next to the wall, and have recently thought of making it pray upon nighly wanderers and attack them with my electronic airsoft gun using a darlington pair transistor to trigger the gun. I belive the best way is to use the infrared frequency accociated with the human body tempeture which I believe to be aroun 2-20:mu:m. I have just now received 10 Heimann LH1878 PIR sensors in the mail which are supposed to get the job of sensing humans quite well. I quickly noticed the 3 pin package. I experimented for a while to conclude that they were polarized. I was hoping to use two of these sensors at the front of my robot to, when triggered, to center and balance the target between equal values of the pir sensor, then attack.

    Problem: I am not familiar with the PIR sensor pin setup

    ( I hope the directional detecting involved with the sensor is adequate)
    Anyway, Much help is appreciated
    Last edited: Dec 1, 2007
  2. johnjohn

    johnjohn New Member

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    Here are some of the PIR specifications,

    MANUFACTURER PART NUMBER:
    LHI878/3902 (PERKINELMER OPTOELECTRONICS)

    DATA SHEET: http://www.electro-tech-online.com/custompdfs/2007/12/Perkinelmer_Actives-and-Passives_9800026.pdf


    I believe I have wired this sensor properly but still I have not seen any resistance, voltage or current change on the device. I made the ground pin negitive, the positive pin positive, and I changed the output from ground, and then later to positive. I saw no electrical changes from the output pin to either the positive or negitive supply when I covered the PIR from light, moved my hand over it, or turn a lighter on right over it. The PIR does not appear to work. Please help....:)
  3. HarveyH42

    HarveyH42 Banned

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    First, suggest you get a datasheet. Got a hunch you aren't familar with the raw sensors. You need a bunch of other support to use them, but fortunately you can get most of that on a single chip.

    I've got a similar project in the works, but for scaring off the neighbor's cats. I've got two modules from Futurlec, $6.90 each.
    http://www.futurlec.com/PIR_Sensors.shtml

    I could be wrong, but get the impression that if the sensor is moving, you'll get a lot of false readings. So mine are stationary, a servo motor will sweep right or left while the gun fires. Was all set to stuff the gun in a piece of 4" PVC, but couldn't cut it down small enough. Guessing I'll need to cut a big hole in the side of the PVC, or find some bigger pipe.

    Find and read the datasheet for your sensors, as you will need to know what kind of signal to expect, timing, pinout, and power requirements. Sounds worse then it probably is. My modules are tiny, and not a lot of parts. You'll need to find out which chip will work best, but you probably want your own circuit for what you want to do. The modules I have need 5 seconds between triggering.
  4. johnjohn

    johnjohn New Member

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    Looked through somemore datasheets but none say the delay time or other special facts like that. Are we speaking of the same item? The cheap $1.50 PyroElectric sensor things with 3 pins?
  5. HarveyH42

    HarveyH42 Banned

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  6. johnjohn

    johnjohn New Member

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    Thanks! The link really helped (along with some personal research). I found that I had no apparent results because:
    a) The output was microscopic and needed amplification, and
    b) It's a differental sensor
    With 2 sensors in the 1 screen package, the PIR is triggered by one side of the sensor being "more different" than the other. I had to put an Infrared opaque material inbetween the two sensors(guessing where halfway was) so that if a human was to the left of the sensor, the right side wouldn't "see" the human on the left side, causing the two sensor sides to be equalant in output. Since the sensor's internal transistor (FET) is a differencial transistor, there is no differance to amplify resulting in no signal. So after I applied the 2ndary amplifyer and "signal sheild", it worked. I think a fresnel lens would do better than a sketchy homemade divider though.

    :) :) Anyway thanks for the lots of help :) :)
    Last edited: Dec 1, 2007

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