Water Level Indicator and Detection Circuit for Air Cooler & Roof Top Tank

While filling up the cooler or while the water goes below the critical level the only way to understand is the mechanical water indicator of the cooler. If we fill the tank with excess water the tank just overflows which causes a mess inside our home, if the water goes beneath a certain degree pump could suck the dust and dirt from the bottom of the tank of the cooler - I need a water level indicator. The idea I have thought would be executed as follows: A system that senses the water level 'High', sounds an alarm for 10 seconds and when the level goes below critical, it also sounds for 10 sec to notify. This idea solves all the water level problems I have mentioned earlier. If you want then you can even implement this technique in the water tank of your rooftop or wherever it is, to detect the water level.

First of all, Watch the Video.

1 X LM 324 Op-Amp

3 X BC547 Transistor

2 X 33uf Capacitor

2 X Buzzer

5 X 10K Resistor

3 X 4.7K Resistor

1 X 1K Resistor

2 X 470K Resistor

1 X 10K Trimmer

I have used all the op-amps in the voltage comparator configuration. You can visualize from the above diagram that op-amp U1.1 is used to sense the water level 'High' and U1.2 detects 'Low'. U1.3 and U1.4 are used to configure the 7 to 10seconds timers. For detail explanation, you can read this article.

Sensor 1 is 'common' that flows a little bit of current into the water which the rest of the sensors will detect. Sensor 2 or S2 detects water level 'High' and Sensor 3 or S3 detects water level 'Low'.

Sensor 1 aka common terminal should be drowned to the nearest place of the bottom of the tank.

Sensor 3 aka 'Low' water level sensor should be placed a bit above from the pump's suction area.

Sensor 2 which detects the level 'High' could be placed just below the overflow cutout of the cooler body.

After taking the measurements between the cooler's overflow cutout to the bottom of the tank and from the bottom to the pump's suction area, I got respectively around 3.7 inches and 0.85 inches. To keep these values in mind I have used a PVC pipe and drilled holes in suitable locations to fit all the sensors. By the way, I have used stainless steel nuts and bolts as the sensors in this case.

To mount this PVC Pipe inside the body I have designed a holder in fusion 360.

After around 3Hrs of soldering the final product is almost prepared.

As a power supply, I have picked up this 5V 0.7A power adapter of an old mobile phone. By stepping up the voltage at 12V with an MT3608 boost converter I could easily power up the circuit.

Ofcourse using such a naked circuit inside the air water cooler isn't a good idea so I have designed a 3D-printed case with 3 mounting holes so that I can slide zip ties through them to hold the case in the right place. I have also designed another small one for the power supply and the boost converter.

After connecting the power and sensor wires, The Project is almost done.

Setting up all the sensors with a PVC pipe is actually a terrible idea that I have realized after a few days of usage. Just think of it I filled the tank and one by one all the sensors and the PVC pipe is drowned. After a while, when the water level is dropping sensors are exposing to air but the PVC pipe isn't Immediately dried out. It holds the water which leads to current flow through the water and finally through the sensors and circuit and that causes error and malfunctioning. You can understand it better from the video above.

However, that might not be the case for the water 'Full' detection sensor because it is set way above from the common VCC aka Sensor 1. So, it gets the time to release the water but the 'Low' water level detection sensor creates problem. The PVC pipe in that section might not get sufficient time to dry out. so when water goes below the sensor it will not be detected immediately until this section is completely dried out.

The AC wiring is pretty straightforward the circuit is directly powered from the AC mains inside the cooler. No switch and nothing in between. When I plug-in the cooler it will Immediately turn on. This is the simplified diagram. The pump is in the series with the circuit as shown in the scheme.