Recently I have been kicking myself for forgetting to turn off the motor that pumps water from a sump to an overhead tank at home. Every time I turn on the motor, I try to remember to turn it off in 30 minutes (about the time it takes to fill up the overhead tank from empty to full), but I keep forgetting to turn it off most of the time, wasting a lot of water before I realize it. Then I got an idea. Why not just make a simple, cost effective timer circuit that will turn off the motor after say 30 minutes? So I started thinking about it. All I need is a 555 timer and the correct resistors and capacitors that will delay the timer for the exact time I want the motor to stay on. Next I need a relay to control the motor. First the timer has to run in monostable mode. We just need a one-shot pulse. The pulse should be long enough to keep running the motor. Next we use t = 1.1RC to get the approximate time (in seconds) the output of 555 timer will be high based on the R (in ohms) and C ...
Life is complex, it has a real part and an imaginary part.