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Have a question about Sensors? Ask our expert Jane Awittor

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Jane's Expertise:image Sensors.

 

About Jane:

Jane is a technical specialist for Panasonic, supporting a broad line of sensors such as pressure, passive infrared, active and infrared array sensors.  Whether it’s a new design or an upgrade to existing design, Jane has the technical expertise to support customers with their various sensor requests.

 

She is an electrical engineer with 5 years of experience specializing in Passive Infrared (PIR), Infrared Array and Pressure Sensors. Focused on technical sales support and interface to research and development teams in Japan. Developed proposals for new product enhancements, competitive product studies and SWOT analysis.

 

 

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  • Hi Jane,

     

    I am hoping you can help me with a problem.  I am using an AMN31111 PIR sensor from Panasonic.  I have it connect to a 5V source, with the output connected to an LED (via a resistor) to light when the sensor detects movement.

     

    When I wire it up this way, the LED flashes in a repeating pattern over and over.  If I stand in front of the sensor, the LED does stay on (mostly), but still flickers a little. 

     

    I am wondering whether I have misunderstood the design of the sensor.  I was planning to wire it into a GPIO port of a raspberry pi (via a resistor to bring the voltage down to around 3V when high).  However, this repeating pattern of high/low has me stumped.  According to the data sheet, the sensor should only make the output go high on movement and should be open line when there is no detection of movement.

     

    I have tried repositioning the sensor pointing across the room, and even outdoors at night time with nothing in front of it of course.  It doesn't change the repeating pattern.

     

    Could you possibly advise of what I might have done incorrect?  I purchased two of these sensors and they both behave the same way.

     

    Thanks.

     

    Damien.

Reply

  • Hi Jane,

     

    I am hoping you can help me with a problem.  I am using an AMN31111 PIR sensor from Panasonic.  I have it connect to a 5V source, with the output connected to an LED (via a resistor) to light when the sensor detects movement.

     

    When I wire it up this way, the LED flashes in a repeating pattern over and over.  If I stand in front of the sensor, the LED does stay on (mostly), but still flickers a little. 

     

    I am wondering whether I have misunderstood the design of the sensor.  I was planning to wire it into a GPIO port of a raspberry pi (via a resistor to bring the voltage down to around 3V when high).  However, this repeating pattern of high/low has me stumped.  According to the data sheet, the sensor should only make the output go high on movement and should be open line when there is no detection of movement.

     

    I have tried repositioning the sensor pointing across the room, and even outdoors at night time with nothing in front of it of course.  It doesn't change the repeating pattern.

     

    Could you possibly advise of what I might have done incorrect?  I purchased two of these sensors and they both behave the same way.

     

    Thanks.

     

    Damien.

Children
  • in reply to Former Member

    The sensor specification states that the maximum output current is 100uA so it isn't really capable of driving an LED - if your resistor is at least 60k the sensor would be OK but I'm not sure that you'll be able to see the LED at all. If you buffer the output with a mosfet or transistor for LED driving it would be better. You may also need a decoupling capacitor across the sensor power supply.

     

    MK

  • in reply to michaelkellett

    Hi Michael,

     

    Thanks for your reply.

     

    The PIR is getting its power from the 5V0 pin of a raspberry pi, and grounding through the same device.  It is not otherwise attached to the rpi in any way. 

     

    I am using a 120 Ohm resister between the output of the AMN31111 to the LED.  The LED is quite visible.

     

    But I'm only using the LED to test that the PIR works as I envisaged it would.  The plan is to wire the output of the PIR to a GPIO pin on a Raspberry Pi.  But first, I am trying to understand why the PIR keeps flashing the LED when there is no motion in front of the sensor.  I have tried pointing it into the back yard at night time where I know there is nothing in front of it within its detection range, and yet it still flashes the LED in a repeating pattern as described in my original post.

     

    Any ideas?

     

    Thanks


    Damien.

  • in reply to Former Member

    Hi, In case you would stumble over the same problem and end up here after deep google searches typing "AMN31111 always high" like the above thread initiated by Damien: here's how I worked around the problem: The reason I got always 1 is that there's a need for a pull-down resistor which I hadn't, and you probably neither. One easy way (at least if you are on an arduino, or esp8266, is to use the analogue pin: as soon as I switched to the A1 pin on my esp8266, I could clearly distinguish a "preson in range" signal =1024 from a "no person in range" signal around 5 or more ... I guess the digital input translated the later one into high without the pull-down resistor.