Auto Shut Off timer
Auto Shut Off timer using 555 timer and 4017 counter
This is another easy to build project. You can use this device to switch off any AC load in a fixed duration of time. This approach is very useful in case of overhead tanks. These tanks usually take 10 minutes to get full of water. After 10 to 12 minutes the tank gets overflow result in wastage of water. I was facing the same problem in my home so I decided to solve the problem electronically. It was little difficult to make a water level indicator in my case as the distance between the tank and pump is about four floors of height. So the auto shut off of pump in 10-12 minutes solve the problem in a more cheap and efficient way.
Working
555 timer is wired as astable multivibrator, working as clock source for CD4017 divide by 10 counter. The time period of the clock generated by 555 timer is adjusted through two 470K resistance and capacitor of 100uF/25V, so that it can generate total delay of 10-12 minutes at the output of 4017. As long as the output of 4017 is between D0 to D6 or D7 the transistor is saturated and the relay is energized. As the output goes beyond D7 the transistor goes to cutoff and relay switches to N/C terminal and the load get cut from mains and switch off in 10 minutes.
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