Watchdog timers are commonly used in computer systems to detect if a computer has crashed and is no longer functioning properly. If the computer is indeed locked and cannot provide a reset pulse to the circuit within a defined time range, the timer will time out and activate an alarm. Watchdog timers can also be used by humans. Just like in a computer, if a human does not press the reset button in the circuit below, an alarm buzzer will be activated. This circuit uses two common logic integrated circuits. The CD4060 contains an oscillator and several logic dividers. The output of the first counter is fed to the second timer. Using given component values, the timer is set to time out after 36 hours. It is very easy to change the oscillation frequency or the number of counter stages to program the circuit for longer or shorter times.
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