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8051 reset problem

Discussion in 'Electronic Basics' started by SEB, Jan 25, 2005.

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  1. SEB

    SEB Guest


    I have a circuit for an 8051 type microprocessor which executes a 1 minute
    program and then shuts down completely. I would like to then have a touch
    switch which resets the power supply to begin execution again. I find that
    cutting the power supply and then re-connecting the power supply works, but
    I need to cut the power supply for about 30 seconds before it will reset.

    Since I want the battery to last a long time (e.g. a year or more), I would
    like to take this shutdown approach rather than an interrupt approach. But,
    I would also like to use a touch switch to reset rather than a hard off/on
    toggle switch.

    Any suggestions?

    Many thanks
  2. Andrew Holme

    Andrew Holme Guest

    30 seconds? That's a long recovery time.

    You shouldn't need to interrupt the power supply.

    Doesn't your processor have a reset pin? Can't you wire a push button into
    the power-on reset circuit?

    The reset signal is often taken from the junction of a resistor and
    capacitor, connected in series across the power supply. The manual reset
    button is then connected across the capacitor.
  3. peterken

    peterken Guest

    try using a SR-flipflop of the 4xxx C-mos series (eg 4013)
    these use only uW of power if static
    use the output to control a transistor that switches on the power line
    have the reset controlled by the 8051
    have the set floating or weak-preset towards the touch switch
    (don't forget clamping of the "floating input" to avoid damage! )
  4. SEB

    SEB Guest

    Thank you for the answers, guys! I have enough to proceed.
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