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Raspberry Pi Forum Quick question (hopefully) on PiFace inputs
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Related

Quick question (hopefully) on PiFace inputs

scuffster
scuffster over 11 years ago

I would like to connect an Activ8 PIR sensor (http://www.responseelectronics.com/downloads/13649193548IR110_Activ8_DT_eng.pdf) to my PiFace inputs.

 

I'm powering the PIR sesnor from an externalk 12v supply. This powers the sesnor and the relay coil. The PIR has a normally closed relay, which is opened when motion is sensed. I managed to get this working (without the piFace board) just checking for an input_value on GPIO pin 12 and using the 3v output directly from the Pi to power the circuit. I'd like to move this to the piFace using the inputs on the piFace.

 

How would I do this? I assume this is a similar pattern to this one https://www.element14.com/community/people/ge0rgej/blog/2013/09/08/5--piface-digital-emulator . But it's not clear to me how to power the switched realy circuit ito the sensor and how that circuit should be cxonnected to the input ports inorder to detect when the circuit is open using digital_read(0) in my python code.

 

Any help appreciated.

 

Many thanks

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  • Former Member
    Former Member over 11 years ago

    What is the Vout from the Relay contacts once the PIR has switched??

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  • Former Member
    Former Member over 11 years ago

    Hi!

     

    I know this is an old post.... But I'm trying to do exactly the same as you did/are.  Was wondering if you could share what you found out?

     

    Also how did you connect your Activ8 PIR directly to the PI?

     

    Thanks

    Shyam

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  • Problemchild
    Problemchild over 11 years ago in reply to Former Member

    The Relay function on this PIR is basically the same as a switch  you can connect the PIR relay output across one of the switches and scan for a button press

     

    Check out my teardown for further info:

    http://www.element14.com/community/people/Problemchild/blog/2013/12/25/piface-control-display-tear-down

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  • Former Member
    Former Member over 11 years ago in reply to Problemchild

    Thanks for that John!

     

    Do you know if I can connect this directly to the PI just to play round with it before getting the PIFace?  If so, would you be able to tell me what gpio pins to use?

     

    Thanks

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  • Robert Peter Oakes
    Robert Peter Oakes over 11 years ago in reply to Problemchild

    your link seems to be broken

     

    Peter

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  • Robert Peter Oakes
    Robert Peter Oakes over 11 years ago in reply to Former Member

    the answer to that would be yes, you will need to power the PIR separately and just use the "RELAY" contacts to the PI, one would go to ground and one to the GPIO pin, a pull up resistor to 3v3 of a few K is all the extra you should need.

     

    remember the relay is normally closed meaning it is like the button is always pressed until you sense movement at which point it will open

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  • Former Member
    Former Member over 11 years ago in reply to Robert Peter Oakes

    Thanks a lot peter.  The PIR will be powered by the existing alarm panel.  I assume that the resistor will go between the PIR and the GPIO pin?

    Will the resistor be needed if I was going to use the PiFace?

     

    Fixed link: PIFace Control & Display Tear Down

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  • Robert Peter Oakes
    Robert Peter Oakes over 11 years ago in reply to Former Member

    the resistor will go from the GPIO pin and the PI 3V3 pin also on the GPIO header

     

    connect the relay between the GPIO pin and GND.

     

    then you will read a 0 (Switch Pressed) when no movement detected and when movement is seen the relay will open and the pull up resistor will shift the GPIO pin to 3v3

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  • Problemchild
    Problemchild over 11 years ago in reply to Robert Peter Oakes

    Peter, you can just swap over the resistor and Relay and have the opposite sense so the resistor is connected to ground as a pull down and the RELAY connects the input to Vcc preferably via a small resistor I suppose

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  • Problemchild
    Problemchild over 11 years ago in reply to Robert Peter Oakes

    Link is fixed now

    http://www.element14.com/community/people/Problemchild/blog/2013/12/25/piface-control-display-tear-down

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