Automatic turn off water pump on desired level + water level indicator/sensor

This kit is used to learn how we can use simple cmos 4049 inverter to create latch circuit for turning ON and OFF water pump, sensor and indicator. Also this device uses two different voltage levels for his work. Firstly we use linear regulator to step down 12V DC to 9V DC, that woltage level is used as supply for IC 4049 and LEDs. Second voltage level is 5V and it is obtained with second linear regulator which will step down 9V from first regulator to 5V, those 5V are used as supply for relay module. This two levels are needed because cmos 4049 for his work needs voltage in range from 5V to 16V.

This project is designed around single CMOS Logic Inverting 4049 chip, water pump is turned ON and OFF with relay module while water level in tank is shown with 4 LEDs.

Firstly as sensors for this circuit simple copper wires which are placed on different levels in tank could be used, ground wire is placed at the bottom of tank.

Inputs of logic NOT gates are connected in series with resistors of big value and with positive terminal of power supply, sensor wire is connected between resistor and NOT gate input.

Output of inverting gate is connected with LED and appropriate resistor. So if we put positive voltage on imput of NOT gate we will get negative output so LED diode will not glow.

When water in tank starts to rise it will get in contact with sensor and will ground input of NOT gate and that means that output of NOT gate will change from negative to positive and LED will glow and indicate water level. LED diode and resistor are connected with ground.

Those positive outputs are also used to fed transistor base which then brake latch circuit and turn OFF water pump.

Latch circuit is created with two NOT gates in series and resistor in parallel with them.

Latch is turned ON by getting positive impuls on input of first NOT gate and that positive imput at the output of second NOT gate will activate transistor which will then activate relay module and water pump.

Latch will be broken by grounding imputs of NOT gates with transistor which will be turned on like LED diodes.

If user wants to turn OFF water pump on different level (shown by LED) he can do that by activating DIP switch. To turn OFF pump on first level user needs to slide first switch part ON to turn OFF pump on second level second part should be turned ON and to turn OFF water pump on third level third part of dip switch shold be turned ON (only one part of switch must be turned ON at the same time). To turn OFF water pump on last level all parts of dip switch must be OFF.

Device is connected with relay module using jumper wires. Device gives +5V when water pump should work, those 5V are used to turn ON relay module.

Relay module is used because it is much safer then user side soldered relay on PCB, but still all safety measures should be done!! Incorrect wiring can cause damage to appliances or more importantly, yourself!


zcnabj (Jan 23, 2015)
Hello Bojan,

I tried doing this circuit with all components the same with yours. I am just wondering why sometimes the Relay does not turn on when all DIP switches are set to OFF. When I press the tact switch "ON", the relay turn ON just about 1-2 seconds and then suddenly turned OFF itself

Bojan (Aug 20, 2015)
I have accidentaly deleted previous comment where I described in details what problem occured. I just wanted to ask whether suggestion solved problem.

But this design should work, if it does not work and if someone else have same problem one 10k resistor can be soldered, its one pin on the node between LED4 and R8 and another to ground.