Controlling an electric water pump, to keep a container full of water. Just as in a washing machine, the depth of the water can be sensed from a hose connected to the base of the container.The advantage over a float switch is that the level is easily adjustable. Providing a low water level warning eg, the switch could be used to activate a buzzer or light if the liquid level in a tank drops below an adjustable point.
The master timer is realised with monostable IC 555 (IC1) and its ‘on’ time is decided by the resistance of 1-mega-ohm potmeter VR. A 47-kilo-ohm resistor is added in series so that even when the VR knob is in zero resistance position, the net series resistance is not zero.