When the switch is closed, the CD4010 up/down counter is preset to 9 and the 555 timer is disabled with the output held high.
When the switch is opened, the timer produces an approximate 1 second clock signal, decrementing the counter until the 0 count is reached.
When the zero count is reached, the ‘carry out’ signal at pin 7 of the counter moves low, energizing the 12 volt relay and stopping the clock with a low signal on the reset line (pin 4).
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