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want short pulse on switching circuit on

Discussion in 'Electronic Basics' started by roy davidson, Jul 16, 2005.

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  1. roy davidson

    roy davidson Guest

    I'd like a short high pulse on powering a circuit up, the pulse will reset a
    counter. Something 555 based or simpler would be good.

    thanks roy
     
  2. A simple series RC circuit would surely do the job? Choose R and C
    values to suit duration required. For example:


    5V
    |
    o
    \
    Switch \
    o \
    |
    |
    100 nF ---
    ---
    |
    |
    o------------o Output pulse
    |
    ' approx 1 ms
    |
    .-.
    | |
    10k | |
    '-'
    |
    |
    ===
    GND

    (created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)
     
  3. john jardine

    john jardine Guest

    Main gotcha is that the reset circuit powers up along with everything else.
    Hence must have a clean response from 0V upwards.
    First inverter o/p drops low about 1 sec after power on. Second inverter
    then gives a 10ms high pulse. (times are just offhand values).

    VCC VCC VCC
    | | |
    | .-. .-.
    IN4148 - | |100k | |100k
    ^ | | | |
    | '-' '-'
    | | |\ || | ___ |\
    '---+--| >O----||--+--|___|--| >O---Reset pulse out
    | |/ || 100k |/
    --- 100n
    ---
    | 10u CD40106 hex schmitt inverter
    ===
    GND

    (created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)
     
  4. Terry

    Terry Guest

    On Sat, 16 Jul 2005 09:20:34 +0100, "roy davidson"

    =>I'd like a short high pulse on powering a circuit up, the pulse will
    reset a
    =>counter. Something 555 based or simpler would be good.

    Try a 555 configured as a "power-up one-shot."

    The 555 data sheet should have the schematic. If not, I'll post for
    you.

    I'm using that circuit as part of an interface circuit to an X10 mini
    controller. Works flawlessly.

    Cheers--
    Terry--WB4FXD
    Edenton, NC
     
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