Power button mod ???

Discussion in 'General Electronics Chat' started by SteveDouglas, Jul 16, 2014.

  1. SteveDouglas

    Thread Starter Active Member

    Apr 30, 2009
    42
    2
    I have THESE wireless headphones.

    They have a momentary push power button. I removed the guts from the transmitter and installed them in a small low profile project box so it would fit inside the wall box behind my flat panel HDTV in the bedroom.

    The problem is, lately we've been having some bad storms often and every time the power goes out, even for a moment, I have to swing the tv out and reach in behind it and press and release the power button.


    I'd like to mod it so that when the unit receives power, it turns it self on.

    I program PICs and can solve this with a PIC but I'd like to do it a simpler, quicker way if possible.

    Any ideas ???

    Thanks for any suggestions,

    Steve
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    why not put an electrolytic cap across it to delay the rise in voltage across the switch after power comes back on?
     
  3. john_doe01

    New Member

    Nov 27, 2011
    24
    0
    Would that work?
    with power loss you will be losing the supplies for the entire unit, OP says he needs to press and release the momentary button so doesn't that mean its a soft switch and a cap will do nothing on power up?

    how about a 555 timer monostable circuit giving a pulse to the momentary switch, if you feed it from the main supplies on power up it will give the needed pulse
     
  4. SteveDouglas

    Thread Starter Active Member

    Apr 30, 2009
    42
    2
    Do you know that will work ?

    I don't know if the switch is switching low or high.

    And, I was wondering if the switch was just jumpered, thereby keeping it closed continuously would work or do harm (?)

    EDIT: I was typing while John posted. The 555 will probably work fine, I may do it that way, thanks !
     
  5. john_doe01

    New Member

    Nov 27, 2011
    24
    0
    shorting the switch will have the same result as keeping it pressed in, if the unit can be turned on by holding the switch and not releasing it a jumper will work
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    This is a common problem on small cheap devices, because they use too small a capacitance in the PSU after the bridge rectifier (to save money, big caps cost a lot more). That resets the internal microcontroller in the device.

    If you solder some large caps 2200uF etc inside the device on in the DC power lead (assuming it has a DC plugpack) it will require power outage for a number of seconds to reset.

    You can even get caps in the Farad range. 5v 1F are common enough. They are low voltage and would probably need to go internally on the device's 5v or 3.3v power rail to the micro.
     
  7. SteveDouglas

    Thread Starter Active Member

    Apr 30, 2009
    42
    2
    Thanks Roman, I may try that if jumpering the switch doesn't work.

    BTW: I have your SuperPID on my CNC router and your hall limit sensors, they both are great !

    Thanks again
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Wow, small world! Thanks for the nice words. :D
     
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