Water level automatic control system circuit based on NE555

For beginners in microcontroller development , it is undoubtedly a sense of accomplishment to create a simple circuit to realize the function. In this article, engineers put together a simple automatic controller for water tank water level.

In this microcontroller learning case, it turns the water pump motor on or off when the water level in the water tank is below the minimum level or above the maximum water level . Two floats are used in this scheme to sense the water level to operate the switch used to control the water pump.

1. Water level automatic control system circuit

Each sensor float is suspended from above using hollow stainless steel tubes. This arrangement is wrapped in PVC pipe and fixed vertically to the inner wall of the tank. Such sensors are more reliable than inductive sensors. Sensor 1 senses the minimum water level, while sensor 2 senses the maximum water level (see picture below).

The leaf switches S1 and S2 (used in the recorder) are fixed on top of the sensor unit so that when the float is raised the diameter is 5mm. The (approximately) hollow stainless steel tube pushes the moving contacts (P1 and P2) of switches S1 and S2 from the normally closed (N/C) position to the normally open (N/O) position. Likewise, when the water level drops, the active contacts return to their original positions.

Normally, the N/C contact of switch S1 is connected to ground, and the N/C contact of switch S2 is connected to the 12V power supply . The IC 555 is wired like this: when its trigger pin 2 is connected to ground it is triggered and when its reset pin 4 is connected to ground it is reset. Threshold pin 6 and discharge pin 7 are not used in the circuit.

2. Circuit principle of automatic water level control system

When the water in the tank drops below the minimum water level, the movable contacts of the two blade switches (P1 and P2) will be in the N/C position. This means that the trigger pin 2 and reset pin 4 of the NE555 chip are connected to ground and 12V respectively. This flip-flop NE555 chip is connected to ground and 12V respectively. This will trigger the NE555 chip and its output will go high to power relay RL1 through driver transistor SL100 (T1) . If switch S3 is "on", the pump motor is turned on and begins pumping water into the overhead tank.

As the water level in the tank rises, the float of sensor 1 also rises. This moves the moving contact of switch S1 to the N/O position and the trigger pin 2 of the NE555 chip is connected to 12V. Don't worry, this won't have any effect on the NE555 chip and its output will still be high enough to keep the pump motor running.

As the water level further rises to the maximum level, the float of sensor 2 pushes the movable contact of S2 to the N/O position and is grounded. Now, the NE555 chip resets and its output goes low to turn off the pump.

As it is consumed, its level in the overhead tank drops. Therefore, as it is consumed, its level in the top tank drops. Therefore, the float of sensor 2 also falls. This will move the moving contact of switch S2 back to the NC position and reset pin 4 of the NE555 chip is connected to 12V again. But the NE555 chip will not be triggered because its trigger pin 2 is still clamped to 12V by switch S1. Therefore, the water pump remains off.

When the water level further drops to the lowest level, the movable contact of switch S1 moves back to the N/C position to ground the trigger pin 2 of the NE555 chip. This will trigger the NE555 chip and turn on the water pump.

3. How to build an automatic water level control system

The float sensor unit can be assembled at home. Both units are identical except for the length. The depth of the water tank from the top to the outlet pipe can be used as the length of the lowest water level sensing unit. The depth of the tank from the top to the water level at which the tank is to be filled is considered the length of the maximum water level sensing unit. As shown in the picture above, the blade switch is fixed to the top of the tank.

Each pipe is closed at both ends using two caps. A hole 5 mm in diameter is drilled in the center of the top cover so that a hollow stainless steel tube can be easily passed through it to select the contacts of the blade switch. Likewise, drill a hole in the bottom cover of the pipe so water can enter the pipe to lift the float.

When the water reaches its maximum level, the float should not rise more than the distance required to push the moving contact of the vane plate switch to the N/O position. Otherwise, the pressure on the float could damage the door leaf switch itself. The length of the hollow stainless steel pipe should be selected accordingly. Some glue should be used to secure it to the float.