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TIDA-01069: AND Gate

Part Number: TIDA-01069
Other Parts Discussed in Thread: TIDA-00489, , SN74AUP1G32

Hello, 

Thank you for the TIDA-01069 and TIDA-00489 notes about low power PIR motion detection, that's very interesting.

I just have a question: in the TIDA-01069 you use two outputs from the comparators to the MCU : PIR_OUT_HI and PIR_OUT_LO .
But if you don't need to distinguish between HI and LO (so we don't need to know the movement direction), then I guess we should use an AND gate after the comparators.

Do you have any suggestion about an AND gate that could fit with this design ?

Thank you

Guillaume

  • Guillaume, hello and good morning. I have spoken with a member of our Building Automation team that will be responsible for answering your question.  Name is Brian Dempsey and he should be responding to your query within the next business day. Thank you for your interest in Texas Instruments and our TI Designs! 

    Best Regards,

    John Fullilove

    Manager, TI Designs

    Texas Instsruments

  • Hi Guillaume,

    Thank you for your interest in the PIR designs! To answer your question, the output behavior of the 2-comparators entirely depends on the end-use case,mounting,etc. I think an OR gate may be a better solution than the AND gate. Typically you will see a "high" value on one comparator, followed by a "high" value on the other, not necessarily simultaneously. This assumes the object moves far enough into the IR field to create the signal seen in FIGURE 4 of the TIDA-01069 design guide.

    Now with that being said, there is a period of time in the output where the signal goes back to its original steady state value before the voltage swing to the opposite polarity, also shown in FIGURE 4 of the TIDA-01069 design guide. This means that an AND gate may not provide the desired output in the case of a slower movement across the PIR sensor field. The OR gate on the other hand will alert any time there is a"high" output from either comparator.

    As far as the part recommendation, TI has many great logic parts. What are your system requirements (cost constraint, size, current consumption, etc.)?

    -Brian Dempsey

  • Hello Brian,

    Thanks for your answer.

    Yes, my fault, I looked up a bit too fast at how the comparators were wired and output is high when motion is detected (not low as I thought), so we need an OR Gate.

    Regarding the part choice, we need very low power consumption (to stay in the micro amp range from your PIR design) and an input voltage range starting at 1.8V. I found the SN74AUP1G32 Low-Power Single 2-Input Positive-OR Gate which seems to fit our need. By the way, the logical formula in the sections 3 and 9 of this part datasheet actually describes an AND Gate, there might be an error.
    If you think that an other part would be more fitted to our needs, I'm interested.

    Regards,
    Guillaume
  • Hello Gauillaume,


    Jumping on Bryan's anwser, if you put an AND gate, the ouput will be always 0.

    Indeed, you can not reach in the same time the high and the low threshold of the window comparator.

    So if you want just a binary information that a motion has been detected, you can put an OR gate.

    There is a very interesting application note from Murata on PIR sensor, which might help you to understand much more how it works.

    www.murata.com/.../applinote_pir.ashx


    Thank you,

    Regards,
    Bilal MALIK
  • Hi Bilal,
    Thanks for the sharing the appnote, interesting indeed.

    Regards,
    Guillaume