delayed 555 timer from a high trigger

Discussion in 'The Projects Forum' started by simon_m74vr, Sep 12, 2019.

  1. simon_m74vr

    Thread Starter New Member

    Sep 12, 2019
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    0
    Hi,
    I need to a circuit to do the following:

    When input is high (power on) wait 3 seconds, then pulse an output to a relay for 5 seconds.

    Its to take a TV out of standby automatically.
    When its powered on, a standby LED is on.
    When the standby button is pressed, the LED flashes a few times then the TV kicks into life.

    The standby button does not work for the first couple of seconds - hence the 3 second delay
    The trigger is going to be high - as fed from an LED
    ouput to drive a relay to `press` the standby button for the duration of the LED flashing - that should be ignored by the input.

    Can anyone help please ?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    First couple of seconds from what?
    Are you turning the main's power on and off to the set?
     
  3. dl324

    AAC Fanatic!

    Mar 30, 2015
    8,656
    2,091
    Welcome to AAC!

    From a Signetics Linear Applications Handbook:
    upload_2019-9-12_16-52-27.png
    You need a base resistor on T1.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    What is the supply voltage?
    What is the trigger voltage?
    Can the supply voltage be used as the trigger voltage?
     
    Last edited: Sep 13, 2019
  5. simon_m74vr

    Thread Starter New Member

    Sep 12, 2019
    2
    0
    Thanks all.
    I`m changing my plan... I`m going to use an arduino.

    The trigger will be from the LED as soon as I turn on the mains to the TV.
    Then I`ll program it to wait, then output to a relay for `x` seconds.

    Thanks tho for the 555 help - although I`ll be not using it.
     
  6. danadak

    Distinguished Member

    Mar 10, 2018
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  7. crutschow

    Expert

    Mar 14, 2008
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    Hooray, you found someone who wants to generate a pulse using a microprocessor instead of a 555. :D
     
  8. danadak

    Distinguished Member

    Mar 10, 2018
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    Enjoy your day. :D
     
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