In this post we discuss how to make a simple water level indicator circuit using a single IC 4049 and some LEDs, the later section of the articles also discusses how to upgrade the circuit with a relay controller stage.
There are many posts in this blog which essentially explain water level controller circuits, with the specific intentions of switching the involved motor pump when the tank fills up.
However there are folks who just require an indication of the different levels of water in the tank rather than have an automatic shut off facility.
The switching OFF of the motor is preferred to be carried out manually, which is considered more reliable and safe by them.
The proposed water level circuit idea is specifically suited for the above type of readers who are satisfied with the indications only and want to do the shutting part of the motor manually as per the readings of the indicator and as per the desired water levels in the tank.
- The circuit presented here is again super simple to build, involving only a single IC 4049 for the intended applications.
- The IC as we all know have six NOT gates, these gates are simple inverters, meaning they will invert any voltage level at their input pins to exactly the opposite level at their output pin.
- So if a positive is applied to the input, the output would instantly produce a negative and vice versa.
- The high input impedance of CMOS gates makes sure that potential even with very low currents are suitably sensed and interpreted by them.
- The idea is simple, the ground or the negative voltage (point 0 in the figure) is held at the bottom most part of the tank, such that the water reaches this point first up when it starts filling.
- As the water level goes higher, it subsequently comes in contact with the inputs of the NOT gates arranged serially upwards.
- The negative voltage stationed at the bottom of the tank leaks through the water and comes in contact with the relevant inputs of the gates.
- This negative potential applied at the subsequent inputs of the gates means a production of an opposite voltage, that is a positive potential at their outputs, that's what exactly happens.
- The positive voltage thus generated lights up the concerned LEDs, indicating which input of the gate at what level has come in contact with the rising water level.
- The sensor wire terminals from the circuit in the form of the points 0 to 6 may be arranged over a non conducting stick made up of plastic with brass screw heads fitted as the sensor termination.
- The LED illuminations give a direct indication of the water levels, as these are stationed with calibrated positions in the tank (see circuit diagram)
The pin out diagram of the IC 4049 is given below:
Simulation: A rough simulation of the discussed water level indicator circuit is shown below. We can see how the LEDs light up sequentially in response to the increasing water level coming in contact with the respective sensor points inside the water tank
Image credit: https://en.wikipedia.org/wiki/File:CMOS_4049_diagram.svg
All LED resistors are 470 Ohms,
All gate input resistors are 2M2
All capacitors are 0.1 disc ceramic.
All the gates are from the IC 4049
All LEDs are red 5mm, or as preferred by the maker.
Upgrading to an Automatic Water Level Controller
Now let's try to understand how the above water level indicator circuit concept can be enhanced into a water level controller circuit, by adding a relay system which will switch OFF the motor as soon as the water level reaches the tank brim.
The circuit provided below performs a dual function of both, as an over head tank water level indicator circuit as well as an overflow controller. The indications of the rising water are provided by five LEDs, which light up sequentially in response to the rising water level inside the tank.
How the Circuit Functions
As soon as the water reaches the uppermost level of the tank, the last sensor positioned at the relevant point triggers a relay which in turn switches the pump motor for initiating the required water evacuating action.
The circuit is as simple as it could be. Use of just one IC makes the entire configuration very easy to build, install and maintain.
The fact that impure water which happens to be the tap water that we receive in our homes offers a relatively low resistance to electricity has been effectively exploited for implementing the intended purpose.
Here a single CMOS IC 4049 has been employed for the necessary sensing and executing the control function.
Another interesting associated fact that’s associated with CMOS ICs has helped in making the present concept very easy to implement.
It is the high input resistance and sensitivity of the CMOS gates which actually makes the functioning completely straightforward and hassle free.
As shown in the above water level indicator circuit figure, we see that the six NOT gates inside the IC 4049 are arranged in line with their inputs directly introduced inside the tank for the required sensing of the water levels.
The ground or the negative terminal of the power supply is introduced right at the bottom of the tank, so that it becomes the first terminal to come in contact with water inside the tank.
It also means that the preceding sensors placed inside the tank, or rather the inputs of the NOT gates sequentially come in contact or bridges themselves with the negative potential as the water gradually rises inside the tank.
We know that NOT gates are simple potential or logic inverters, meaning their output produces exactly the opposite potential to the one that’s applied to their input.
Here it means as the negative potential from the water bottom comes in contact with the inputs of the NOT gates through the resistance offered by the water, the output of those relevant NOT gates sequentially start producing opposite response, that is their outputs start becoming logic high or become at the positive potential.
This action immediately lights up the LEDs at the outputs of the relevant gates, indicating the proportionate levels of the water inside the tank.
Another point that’s to be noted is, all the inputs of the gates are clamped to the positive supply through a high value resistance.
This is important so that the gates inputs are initially fixed at the high logic level and subsequently their outputs generate a logic low level keeping all the LEDs switched off when there’s no water present inside the tank.
The last gate which is responsible for initiating the motor pump has its input positioned right at the brim of the tank.
It means when the water reaches t the top of the tank and bridges the negative supply to this input, the gate output becomes positive and riggers the transistor T1, which in turn switches the power to the motor pump through the wired relay contacts.
The motor pump stats and begin evacuating or releasing the water from the tank to some other destination.
This helps the water tank from overfilling and spilling, the other relevant LEDs which monitors the level of the water as it climbs also provides important indication and information regarding the instantaneous levels of the rising water inside the tank.
R1 to R6 = 2M2,
R7 to R12 = 1K,
All LEDs = Red 5mm,
D1 = 1N4148,
Relay = 12 V, SPDT,
T1 = BC547B
N1 to N5 = IC 4049
All the sensor points for this LED water level indicator circuit are ordinary brass screw terminals fitted over a plastic stick at the required measured distance apart and connected to the circuit through flexible conducting insulated wires (14/36).
Practical Tested Prototype
The above circuit was successfully built and tested by Mr. E.Rama Murthy who is one of the regular and dedicated readers of this blog. The following pictures of the built prototype were sent by him, let's investigate the results closely.
Upgrading the Relay Circuit
The above discussed water level indicator with relay control circuit has one serious drawback. Here the relay operation might continuously keep switching the motor ON/OFF as soon the water level reaches the overflowing threshold, and also immediately when the upper level reduces slightly below the topmost sensor point.
This action may not be desirable for any user.
The drawback can be eliminated by upgrading the circuit with an SCR and transistor circuit as shown below:
How it Works
The above intelligent modification ensures that the motor is switched ON as soon as the water level touches the point "F", and hereafter the motor keeps running and pumping the water out even while the water level drops below the point "F" .... until it finally reaches below the point "D".
Initially when the water level goes above the point "D" the transistors BC547 and BC557 are turned ON, however the relay is still inhibited from switching ON because the SCR is switched OFF during this time.
AS the tank fills and the water level rises upto the point "F" output of gate N1 turn positive latching ON the SCR, and subsequently the relay and the motor also switch ON.
The water pump begins pumping water out from the tank which results in emptying the tank gradually. The water level now drops below the point "F" switching OFF N1, but the SCR keeps conducting being in the latched situation.
The pump keeps running causing the water level to drop continuously until it reduces below the point "D". This instantly switches OFF the BC547/BC557 network, depriving the positive supply to the relay, and eventually switching OFF the relay, the SCR and the pump motor. The circuit returns to its original situation.