9 Second Countdown Power-On Relay Circuit
This circuit provides a 9 second delay using a 7 segment display. 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). The relay will remain energized until the switch is again closed, resetting the counter to 9. The 1 second clock signal from the 555 timer can be adjusted slightly longer or shorter by increasing or decreasing the resistor value at pin 3 of the timer.
Note:
- The circuit can be powered from a 9V PP3 battery or 12V DC power supply.
- The time delay can be varied by replace the resistor value at pin 3 IC555.
- The push button switch is for starting the timer.
- The appliance can be connected via contacts relay.
Source: bowdenshobbycircuits.info
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