Push-Button switch with delay to Turn On/Off Raspberry PI

Discussion in 'Analog & Mixed-Signal Design' started by Kevin Pilgrim, Sep 14, 2018.

  1. Kevin Pilgrim

    Thread Starter New Member

    Sep 14, 2018
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    Dear Forum,
    For a mobile project I need a circut to turn on/off a raspberry pi with delay. Idealy with a 2-3 second delay to prevent that a user accidentally powers on or off. Since the PI also has a HDMI Display attached the maxmimum current is 1A. I tried this here http://www.mosaic-industries.com/em...n-switch-turn-on/latching-toggle-power-switch but I did not get it to work.

    I would like to implement it with SMD ic/components.

    Thanks for any helP!
     
  2. Kevin Pilgrim

    Thread Starter New Member

    Sep 14, 2018
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  3. crutschow

    Expert

    Mar 14, 2008
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    Below is a toggle delay circuit that should do what you want.

    U1 and U2 can be any inverting gates, such as a CD4001 NOR gate, or a CD4049 buffer.

    The LTspice simulation shows a delay of about a 2.6 seconds for both turn on and turn off.

    M1 can be just about any logic-level (max Vgs threshold of ≤2V) P-MOSFET with an on-resistance of ≤100mΩ.

    upload_2018-9-14_14-31-21.png
     
    Last edited: Sep 14, 2018
  4. Kevin Pilgrim

    Thread Starter New Member

    Sep 14, 2018
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    Does this look about right ;-)?
     
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    It appears that all the circuits that use logic gates must remain powered even when the switched load is off. Or am I wrong?\

    Ken
     
  6. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    1. Do you want the circuit to wait 2-3 seconds after a brief momentary button push and then switch the power?

    -or-

    2. Do you want the user to have to hold down the button for 2-3 seconds before the circuit switches the power?

    ak
     
  7. crutschow

    Expert

    Mar 14, 2008
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    That will work but you only need one chip, not two.
    There are are 4 gates in each package, and you can use two of them for the circuit.
    Due to C2 and C3, the circuit I posted should come up in the power-off state when the power is applied.
    And it takes only leakage current when energized in the static state.
    Since he stated
    I would think it's number 2.
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    KMoffett said:

    It appears that all the circuits that use logic gates must remain powered even when the switched load is off.

    Due to C2 and C3, the circuit I posted should come up in the power-off state when the power is applied.
    And it takes only leakage current when energized in the static state.


    But you don't show any power for U1/U2. When Vdd is supplied, but the output to the load is OFF, doesn't U1/U2 still have to be connected to Vdd, drawing a small current?

    Ken

     
  9. crutschow

    Expert

    Mar 14, 2008
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    Yes.
    But the CD4011 data sheet states that the quiescent current is less than a microamp, which will be insignificant for all but the smallest battery source.
     
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