PDITEC student community: Water level controller using 555 timer

Water level controller using 555 timer

Components Required

1. Power supply (12v)

2. NE 555 timer IC

3. Resistors (100Ox2, 10kO,1kO)

4. Relay (12V, 30A)

5. SL 100 transistor

6. 1N4007 Diode

Working of Automatic water tank level controller

• We know the property of 555 timer IC, i.e. its output goes HIGH when voltage at the

second pin(trigger pin) is less than 1/3 Vcc.

• Also we can reset back the IC by applying a LOW voltage at the 4th pin (Reset pin).

• In this project 3 wires are dipped in water tank. Let us define two water levels- Bottom (L) level and Top (H) level. One of the wire or probe is from Vcc, which can be called as middle level (M).

The probe from bottom level is connected to the trigger (2nd) pin of 555 IC. So the

voltage at 2nd pin is Vcc when it is covered by water.

• When water level goes down, the 2nd pin gets disconnected(untouched) from water

i.e. voltage at the trigger pin becomes less than Vcc. Then the output of 555 becomes

high.

• The output of 555 is fed to a SL 100 transistor, it energizes the relay coil and the

water pump set is turned ON.

Fig.7: SL 100 transistor

• While the water level rises, the top level probe is

covered by water and the transistor becomes ON. Its

collector voltage goes to Vce(sat) =0.2V.

• The low voltage at the 4th pin resets the IC. So the output of 555 becomes 0V. Hence

the motor will turn OFF automatically.

• For practical implementation, you must use a relay. Rating of relay is chosen

according to the load (Motor). 32 Ampere relay is best suited for domestic

applications.

Probe/Sensor arrangement diagram

The probes can be arranged as shown in the diagram above. Insulated Aluminium wires can be used as the probes. The probes can be binded on a plastic rod and should be erected vertically inside the tank. The length of the probes wires and the supporting plastic rod must be chosen according to the depth of the tank. Since DC is used in the level sensing section electrolysis will occur in the probes and so the probes require small maintenances in 6 or 7 month intervals.