Software self shut down

Discussion in 'Embedded Systems and Microcontrollers' started by rakeshm55, Dec 22, 2010.

  1. rakeshm55

    Thread Starter Member

    Oct 19, 2010
    68
    0
    Hi,
    I want to implement a circuit so that I could initiate self shut down.

    refer to diagram.

    Dc to Dc converter I use for the system has a shut down pin ... but once i turn off (by driving shutdown pin) the system , there wont be any active circuit to drive the shutdown pin as microcontroller switches off. Then the circuit would wake up again and this turns out to be a recurring loop.How to sort the issue?? Wat module I should place b/w uC and Shutdown pin.

    How is shutdown initiated in desktop computers.


    which will be an appropriate IC for this function.....or a standard circuit schematics will do.

    Please help me out.
     
  2. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    A 10k resistor would probably do the trick from the shutdown pin to either ground or 3.7V (whichever shuts down the converter). The micro then also connects to the pin to keep the shutdown pin in the enable state until shutdown is required.
    <ed>Of course this creates more problems because when the battery is first connected the micro won't be able to start. You could add a momentary action push button to briefly enable the shutdown pin to start the micro running. </ed>
     
    Last edited: Dec 22, 2010
    rakeshm55 likes this.
  3. rakeshm55

    Thread Starter Member

    Oct 19, 2010
    68
    0
    Hi,
    Wat will happen if watch dog times out ?
    Wont the microcontroller enter into reset mode where the shutdown would be asserted thus entering a dead loop of self killing??
    Or is that a soft reset would bypass the trouble for me , I am using internal watch dog timer and Power on reset ......

    Even if it is hard reset cant I avoid such spurious cases with appropriate logic ??

    please help
     
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    what is your startup method?

    I would think that a selfholding latch circiut for startup, which, when broken, can only be restarted by your startup method.
     
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  5. rakeshm55

    Thread Starter Member

    Oct 19, 2010
    68
    0
    Hi,
    Is self holding latch circuit a relay?? ... or are there IC's available for this function. .. sorry for my naivity but please do help me.....
    As of now I followed the scheme suggested by "Markd77".... by using a push button switch and pull down resistor preset shut down mode to DC to DC converter......

    my reference is all to how laptop wakes up using power on switch, its s/w shutdown feature and power off by pressing the same power on switch...

    I want to implement the same scheme in my module.... one power on switch for shutdown, s/w shutdown and POWER off.....
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    You need to implement that in software with sampled pictures of the button state and timing loops that tell the micro what function to perform.

    Outside the micro, in discrete component land, you would need a timing circuit(555 most likely) and logic gates to select the appropriate function if you don't do it in the software.

    Google might give you some ideas "multi function power button" or something like that.
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Often, laptops and the such, put the system into a "sleep" or "hibernate" mode rather than a complete power off.

    I am not sure if there is a register you can hit to kill the power (Like the "poke something" command in the old VIC20 would power off)

    May be worth checking.

    Other than that, I would try to trigger a transistor that would kill the power to the chip.

    A logical '0' to VCC should kill the power. A button to charge the gate of a mosfet could "re-power" the uC.
     
  8. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    How about;

    You depress your ON/OFF button which applies power to the Uc which in turn starts up, queries it's start up status, enables the main power, and updates it's startup status. This all happens while you are depressing the ON/OFF.

    On the shutdown cycle, when you depress the ON/OFF for a specified time, the Uc queries its startup status, recognizes it's on going to off, does it's shutdown housework, then releases the main power latch. It will idle until your release the ON/OFF button.
     
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