Motor dry Running, Tank Overflow Water Level Controller Circuit

The post explains a very simple water level controller circuit which is able to implement and restrict overhead water overflow as well as dry running of the pump motor. The idea was requested by Mr. S.R. Paranjape.

The Request

Dear Mr.Swagatham Majumdar,

I came across your site while searching for Timer circuit. I am very surprised by seeing how much one individual can do!

I refer to your write up of Friday 20, 2012.

I have a similar problem. I have a designed a circuit, which appears to work on breadboard.I want to start pumping only if there is a need in upper tank and lower tank has enough water. Further if water in lower tank goes below certain level while pumping, the pumping should stop.

I am trying to find a way for satisfying my last condition. 

I want to start this circuit manually and when the circuit stops pumping action, it should also nullify my start action. This will stop the total operation of filling the upper tank.

Somehow I feel that combination of two relays( outside the circuit) in ON/Off part of total project should work. I am unable to figure how so far.
The above drawing may express what I want.Project/circuit is powered by the outer source. The output(that is used to stop umping) from the circuit should open the outer source, which was activated manually.

I hope you will excuse me in taking this root to pose my problem. If you find merit in my problem, you are welcome to put it on your blog.

I am attaching the circuit that I have devised.

As an introduction to myself- I am senior person(age 75 years) and has taken this as hobby to use my time interestingly.I was Professor of Statistics, University of Pune.

I enjoy reading your projects.

Thanking you

S.R.Paranjape

The Design

I appreciate the effort from Mr. S.R. Paranjpe, however the above design may not be correct due to many different reasons.

The correct version is shown below (please click to enlarge), the circuit functioning may be understood with the help of the following points:

The point "L" is positioned at some desired point inside the lower tank, which determines the tanks lower water level at which the motor is in the permitted zone of operation.

 The terminal "O" is fixed at the topmost level of the upper tank or the overhead tank at which the motor should halt and stop filling the upper tank.

The basic switch ON sensing is done by the central NPN transistor whose base is connected to point "L", while the switch OFF action is performed by the lower NPN transistor whose base is connected to point "O".

However the above operations cannot initiate until the water itself is supplied with a positive potential or voltage.

A push-button switch has been included as requested for facilitating the required manual start function.

On pressing the given push button momentarily, allows a positive potential to enter the tank water via the push button contacts.

Assuming the lower tank level to be above the point "L" allows the above voltage to reach the base of the central transistor via the water, which instantly triggers the central transistor into conduction.

This triggering of the central transistor switches ON the relay driver stage along with the the motor, and it also latches the relay driver transistor such that now even if the push button is released sustains the operation of the circuit and the motor.

In the above latched situation, the motor halts under two conditions: either the water level goes below the point "L" or if the water is pumped until the overhead tanks upper limit is reached, that is at point"O"

With the first condition, the voltage from the relay driver collector is inhibited from reaching point "L" breaking the latch and the motor operation.

With the second condition, the lower BC547 gets triggered and breaks the latch by grounding the central transistors base.

Thus the overhead water level controller circuit is allowed to remain operational only as long as the water level is at or above point "L" or is below point "O", and also, the initialization is solely dependent on the pressing of the given push button.

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