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Circuits designed by David Johnson, P.E.
Last Updated on:
Saturday, December 23, 2017 03:21 PM
List of Dave's Circuit Designs
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More
Timer Circuits
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36 Hour Watchdog Timer
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| A watchdog timer is often
used in computer systems to detect when a computer is hung up and is no longer running
properly. If it does become locked up and is not able to supply a reset pulse to the
circuit within a defined time frame the timer times out and activates some kind of
alarm. Watchdog timers can also be used for humans. As in the computer, if
the human fails to press the reset button in the circuit below, an alarm buzzer is
activated. The circuit uses two common logic ICs. The CD4060 contains an
oscillator and a number of logic dividers. The output of the first counter is
fed to the second timer. With the component values given, the timer is set for a
timeout after 36 hours. It is very easy to change the oscillator frequency or
the number of counter stages to program the circuit for longer or shorter times.
I have supplied the formulas for determining the component values. |
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Click
on Drawing Below to view PDF version of Schematic |
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