Motion Sensor/555 Timer Project

Discussion in 'The Projects Forum' started by iONic, Nov 17, 2013.

  1. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    For a while I had a battery operated motion sensor/alarm device outside on my deck. I did a great job detecting the presence of my dog when he wanted to come back inside. This allowed me to keep the door shut, keeping the flies out and the cold out. I rewired the pizo output to sound inside the house so I could hear it.

    But two things were issues...

    1) the alarm was constant as the dog continued to move
    (Ideally, I'd like it to sound for a couple seconds every 20 sec)

    2) the device was cheap and decided not to function well if the humidity was
    too high.
    (Ideally, this time I want just a water tight sensor outside and the remaining
    electronics inside powered by a 5V wall supply)

    So my objectives are as followed.

    Detect the dog at the door.
    Alarm sounds for a couple seconds
    Alarm is silent for 15 sec
    If motion is still present repeat the cycle

    The specs on the PIR are:
    Working voltage: DC 4.5-20V
    Static current: <55uA
    Electronic level output: High 3.3V/Low 0V
    Trigger mode: Repeated triggering
    BLockade time: 2.5S
    Detective angle: <100°
    Induction distance: less than 3m
    Working temperature: -20---+80

    I will need multiple 555's and be able to trigger with a +3.3V

    I have no starting circuit yet, but will be working on it today.

    The output will be a Pizo(i think) from a old smoke detector.

    Thanks

    i
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Do you need something like this ebay
     
  3. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    Yes, that is sort of what I need. BUT!!! That's what I had....cheap Chinese junk, and it didn't last in the harsh Vermont winters, covered from the elements.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    OK the if you use a pir module like this, and connect your 555 timer with a transistor buffer to trigger it to your desired time, you will need to put it in a weatherproof container.



    555 how to use
     
    Last edited: Nov 18, 2013
  5. elec_mech

    Senior Member

    Nov 12, 2008
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    There are a number of ways to approach this. I've come up with a rather simple one to make things easy. The schematic below is for a 555 in astable mode with a low duty cycle. When motion is detected, pin 4 goes high turning the 555 on. The 555 will output ~2.3 second pulse, wait ~15.4 seconds, then repeat for as long as motion is detected. I've shown a 6VDC buzzer attached to the output. If you prefer to use a piezo, we'll need to add another 555 to generate a ~3kHz signal to drive the piezo.

    Note I reference a Parallax PIR sensor, Rev. B. RadioShack used to sell this, but now carries their own brand which is designed to work at 3.3V or 5VDC. If you decide to use a PIR other than the one I call out, but mindful you may need to step down the voltage from your power supply. Since PIR sensors do not require much in the way of current, this can be accomplished with a Zener diode and a resistor.

    If the buzzer you decide on requires more than ~100mA, you'll want to use a transistor between the 555 and the buzzer.

    Hope this helps and let us know if you have any questions.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Is the specified "Blockade Time" the time the PIR stays triggered, or the minimum interval between successive triggerings?
     
  7. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    Thanks Dodgydave, this is the kind of PIR I already have and do intend on making it water-PROOF.


    elec_mech,
    Very nice. I thought I'd need two 555's for the timing aspects alone. I do have 556's also and can
    use one to generate 3Khz signal.



    Alec_t,
    Honestly, I do not know the answer....didn't even know what "Blockade Time" was...


    Update:
    I was in the process of disassembling the existing "faulty" motion sensor device so as to isolate just the PIR sensor section and place it alone outside.

    The PIR was on a separate 1-by-1in board but contains seems to require 5 wires to interface (Vcc, Gnd, and three outputs). Don't know if all three outputs are being used or not. I was going to use a flexible telephone line (phone to wall type) for wire, but the one I have has only 4 wires in it.

    Seems to me that building it will be simple enough.
     
  8. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    Elec_Mech,

    Thanks for the circuit. Oddly enough, this is pretty much exactly the same circuit I used to build a "mole chaser" that I buried in the back yard. See what happens when you don't use the knowledge you have.......gone!
     
  9. elec_mech

    Senior Member

    Nov 12, 2008
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    Tell me about it - I'm now keeping a binder of all the really useful things I learn here so I can quickly refer to them later. :)
     
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