Generally, water stored in overhead tank is wasted due to over flow ,when the tank is full. Water level alarm using micro-controllers like 8051 and AVR are shown in previous articles.This article shows simple circuits of water level indicator with alarm.
Three circuits were shown here are simple and built using transistors, 555 timer and ULN2003 IC. First let us build a water level alarm using simple transistors.
Water Level Indicator Using Simple Transistors
- BC548 transistors-Q1,Q2,Q3,Q4
- Resistors R1,R2,R3,R4-2.2kohms
- R5, R6 ,R7 – 100 ohm
- Led – Red(LED3) , Green(LED1) , Yellow(LED2)
- Metal Contacts – M1,M2,M3,M4.
- The circuit is designed to indicate three levels of water stored in the tank: low but not empty, half and full but not overflowing.
- When there is no water in the tank, all the LEDs are off as an indication that the tank is completely empty.
- When water level increases and reaches M2, the contacts M1 and M2 get shorted as water acts as a conducting medium between M1 and M2.
- This will turn on the transistor Q1 and the Green LED starts to glow. As the water level continues to rise and reaches half the tank, M3 will come into contact with water and receives a small voltage from M1.
- As a result, Q2 is turned on and Yellow LED will glow. When the water in the tank rises to full tank, M4 is also shorted with M1 and both Q3 and Q4 will turn on.
- The Red LED glows and also an alarm is made by the buzzer as an indication that the tank is full and the water pump or motor can be turned off.
Note:This circuit does not show a buzzer.Connect a Buzzer,resistor and transistor in series and connect this in parallel to the last LED.
Water Level Alarm Using 555 Timer
Here is the circuit using 555 timer IC.
- NE555 Timer
- R3-570 Ohm
- Capacitor- 1UF
- Connecting wires
The two probes which are shown in the circuit should be kept at the high level for the water. The distance between the probes should be less than a few centimetres to ensure that the conduction between the probes will take place when water is touched to these probes.
When the water level rises to the height of the probes, then the 555 circuit will get enabled and the output of the 555 timer produces a square wave output with a frequency of about 62 Hz. This output is given to the buzzer.
The logic Implemented in this circuit is, 555 timer is enabled when its reset pin is connected to logic high. But initially it is connected to ground. When the water level is maximum this pin is enabled and this drives the 555 timer into astable mode.
Water Level Indicator and Alarm Using ULN2003
One can implement this circuit using simple ULN2003 IC.IC ULN2003 consists of an array of seven Darlington transistor pairs.
- R1-R3-1k ohm
- M1-M7-Metal Contacts
- ULN2003 IC
- This circuit can be used to indicate three levels of water in tanks.
- When metal contact is reached ,each Led starts glowing.
- When the tank is full buzzer starts ringing along with this all LEDs are ON.