Float Switch Water Level Controller Circuit

The post narrates a simple water level controller circuit using a float switch mechanism. The idea was requested by Mr. tpraveenraj.
The Request

Hello Swagatam,

I'm a electronic hobbyist from software field. So I try with the things in the weekend. I saw your blog recently and really admired to test this circuit, and when I went to the market I saw the float switch there.

Can I connect that to this circuit, or else will you please suggest me the way to use that, since we don't have to worry about the corrosion & passing currents to water by using this switch.

Thanks for your great works, they are really helpful for the people like us to learn.

The Design

The proposed water level controller circuit using a float switch is basically a semi-automatic system where the pump is started manually by press of a button, once the water level reaches the brim of the tank, the operation is switched of automatically by means of a float switch.

Referring to the diagram shown below, the various stages and functions may be understood with the help of the following points:

The left side of the image a shows the tank half filled with water along with the associated float and switch mechanism.

The float mechanism basically consists of a smooth cylindrical water sealed plastic pipe, clamped erect inside the water tank inner base.

A plastic water-tight float surrounds this pipe and is able to slide up/down freely in response to the water level inside the tank. The float being made up of plastic floats at the water surface and is consequently pushed upwards or downwards across the plastic pipe depending upon whether the water is being filled or consumed from the tank.

The float also has an embedded permanent magnet at its upper surface.

The plastic pipe has an in-built reed switch assembly at the top located just near brim of the tank.

The above two counterparts are intended to interact with each other when the water reaches the upper edge of the tank.

When this happens, the magnet inside the float reaches at a close proximity to the reed switch, closing its contacts and thereby causing the wire terminals to get shorted across these contacts.

The right hand side of the diagram is a transistorized latch circuit.

When the tank is empty and is required to be filed, the push button is pressed manually.

Pressing the push button latches the base of T3 and activates the relay which switches ON the motor and holds it in that position until the water in the tank is filled upto the tank brim wherein the float switch triggers the reed relay as discussed above.

The reed switch shorts the connection between the base and ground of T3, rendering the latch inactive which breaks the whole operation.

The relay and the pump motor are thus switched OFF until the push button is pressed yet again for the next cycle.

C2, C3 make sure that the circuit does not get activated by false or spurious electrical disturbances.

Parts list for the float switch water level controller circuit

R2, R3 = 10k

R4 = 100k

C2, C3 = 100uF/25V

D1 = 1N4007

T3 = BC547

T4 = 2N2907

RL1 = 12V relay, 30 amps

switch = any push-to-ON switch, bell switch type

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