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Automatic water level controller using 555 timer IC.
Introduction- The automatic water level controller is used to maintain the water level of the tank automatically. These projects mainly control the pump through relays which is used to feed the water to the tank.
The main component of this project is “555 timer IC”. The output signal which is based on the input signal from the tank is used to control the relay which in turn controls the pump motor circuit.
The 555 timer is a monolithic timing circuit that can produce accurate & highly stable time delays or oscillations. This timer basically operates in one of the three following modes:
 Monostable mode.
 Astable mode.
 Bistable mode.
“Technical specification”
• operating range -55o to +125oc
• Operating voltage +5v to +18v
• Adjustable duty cycle
• µs to hours delay in the output
• Source and sink current 200mA (max.)
• Compatible to TTL as well as op-amp & others circuits.
Circuit diagram of 555
Circuit diagram for automatic water level controller
Working:-The working of this project is based on utilizing the bistable mode of the 555 timer IC. In the bistable mode the 555 gives both the positive and negative supply continuously until it is not trigged.
The triggered voltage is provided from the tank as shown in the figure when water reach the upper level it established the connection of the control signal to the threshold pin and hence the relay disconnect the circuit of the motor with the supply. In the similar manner when the water level reaches below the lowest level it provides the trigger signal to the 555 and once again the connection is between the motor and supply is re-established through the relay which is controlled by 555.
Working of the RS Flip flop:-
R S Output
0 0 0
0 1 1
0 0 Previous stage
1 0 0
0 0 Previous stage
SENSOR: The sensor used in the project uses the bouncy of the water in order to connect the various connections used the timer IC. The sensors are the same that is used now days in the automatic tank connected water filters. Each sensors float is suspended from above using an aluminium rod. This arrangements encased in a PVC pipe and fixed vertically on the inside wall of the water tank. Such sensors are more reliable than induction-type sensors. Sensor1 senses the minimum water level, while sensor 2 senses the maximum water level(see the figure).Leaf switches S1 and S2 (used in taperecorders) are fixed at the top of the sensor units such that when the floats are lifted, the attached 5mm dia. (approx.) aluminium rods push the moving contacts (P1 and P2) of leaf switches S1 and S2 from normally closed (N/C) position to normally open (N/O) position. Similarly, when the water level goes down, the moving contacts revert back to their original positions. Normally, N/C contact of switch S1 is connected to ground and N/C contact of switch S2 is connected to 12V power supply. IC 555 is wired such that when its trigger pin 2 is grounded it gets triggered, and when reset pin 4 is grounded it gets reset. Threshold pin 6 and discharge pin 7 are not used in the circuit. When water in the tank goes below the minimum level, moving contacts (P1 and P2) of both leaf switches will be in N/C position. That means trigger pin 2 and reset pin 4 of IC1 are
connected to ground and 12V, respectively. These triggers IC1 and its output go high to energise relay RL1 through driver transistor SL100 (T1). The pump motor is switched on and it starts pumping water into the overhead tank if switch S3 is ‘on.’ As the water level in the tank rises, the float of sensor 1 goes up. This shift the moving contact of switch S1 to N/O position and trigger pin 2 of IC1 gets connected to 12V. This doesn’t have any impact on IC1 and its output remains high to keep the pump motor running. As the water level rises further to reach the maximum level, the float of sensor 2 pushes the moving contact of switch S2 to N/O position and it gets connected to ground. Now IC1 is reset and its output goes low to switch the pump off. As water is consumed, it level in the overhead tank goes down. Accordingly, the float of sensor 2 also goes down. This causes the moving contact of switch S2 to shift back to NC position and reset pin 4 of IC1 is again connected to 12V. But IC1 doesn’t get triggered because its trigger pin 2 is still clamped to 12V by switch S1. So the pump remains switched off. When water level further goes down to reach the minimum level, the moving contact of switch S1 shifts back to N/C position to connect trigger pin 2 of IC1 to ground. This triggers IC1 and the pump is switched on. The float sensor units can be assembled at home. Both the units are identical, except that their length is different. The depth of the water tank from top to the outlet water pipe can be taken as the length of the minimum-level sensing unit. The depth of the water tank from top to the level you want the tank to be filled up to is taken as the length of the maximum-level sensing unit. The leaf switches are fixed at the top of the tank as shown in the figure. Each pipe is closed at both the ends by\using two caps. A 5mm dia. hole is drilled at the centre of the top cap so that the aluminium rod can pass through it easily to select the contact of leaf switches. Similarly, a hole is to be drilled at the bottom cap of the pipe so that water can enter the pipe to lift the float. When water reaches the maximum level, the floats should not go up more than the required distance for pushing the moving contact of the leaf switch to N/O position. Otherwise, the pressure on the float may break the leaf switch itself. The length of the aluminium rod is to be selected accordingly. It should be affixed on the metal/thermocole float using some glue (such as Araldite).