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By using a capacitor as a timer. While the pushbutton isn't pressed, the capacitor is in charge. When you press the button, a CMOS inverter disable the charge and a transistor discharge the capacitor slowly using a 2,5 K resistor. During this second of discharge, the capacitor turn on a load using an nMOS, but when it is discharged (1 second later) the LED will be turned off. If you release the button, the transistors charge the capacitor again and you can press another time the button.
To increase this second you can change the 2,4 K resistor or the capacitor. If the resistor is smaller than 2,4 K, you can have less than a second of pulse, if it's bigger, you can have more than 1 second.
The 555 IC is in monostable mode and run to transform the wave to a pulse of 1 second (square wave).
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