We already had a good number of water projects and this is not just one more. This circuit gives continuous indication of six levels of water in the tank using ordinary wires as probes. Probe at the highest level can also give an alarm indicating water reached maximum level. The probe at the lowest level gives another alarm indicating low level. All the levels can be individually set and alarm set points also can be changed.
This circuit is built around IC CD 4050 (Hex BUFFER). Pin out of the IC is given in Figure and the circuit in Schematic.
CD4050 has six separate buffers in a single package. In a buffer, if the input level goes high, output also goes high. Similarly if the input level goes low, output also goes low. On the contrary, in an inverter (CD4049) if the input level goes high, output goes low. Similarly if the input level goes low, output goes high.
The five input probes are just wires fixed at appropriate levels in the water tank and the wire from the POWER SUPPLY LINE is fixed at the bottom most position as a reference. All the inputs are kept low through 3.3M resistance (R1-R6) and the output pins will be all low as long as there is no water level at any probe. Hence level indicating LEDs do not glow.
As soon as water touches any probe, corresponding input reaches high level and its output also turns high. This results in glowing of respective level indicating LED in turn. Probe at U1A pin is at the lowest level. When the water level falls below this, corresponding LED 1 will not glow.
Probe of U1B pin is placed at one step above the lowest level so that it gives an advance indication of the impending low level. As long as the water is at this level, green LED 2 glows. If the water level falls below this, this LED no longer glows. As there is now a low level at this output, Q1 goes into conduction and drives Piezo buzzer BZ 1. It continues to ring until water level touches this probe.
Probes of U1F pins are at the highest level. Whenever water touches high level probe here, LED6 glows indicating high-level water. This also triggers the transistor Q2, and buzzer BZ2 .
goes on. It is essential that the tones of both the buzzers are different such as continuous, intermittent or musical tones to give different indications for high and low levels.
This circuit can be operated on 12V power supply, even half wave. Use of batteries is also good. Probes can be simple hook up wires with the ends scratched. You may have to clean them when occasionally they get coated.
It will be a good idea to place a probe at one step above the bottom most level. It gives an advance alarm indicating that the level is just about to drop down. Water tanks go empty just as the guests arrive or when we need water badly. To add to our travails, power also fails at that time as if design. This idea gives time to fill the tank early. Of course there is an LED indication at the bottom most level.
Other ICs like CD4069, 4049, also can be used for this application. Make suitable changes following the appropriate pin-out and application notes.
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