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L70, Water Level Indicator Type-9

A simple but very reliable and effective water level controller circuit diagram is shown here. The circuit uses 6 transistors, 1 NE555 timer IC, a relay and few passive components. The circuit is completely automatic which starts the pump motor when the water level in the overhead tank goes below a preset level and switches OFF the pump when the water level in the overhead tank goes above the full level.


  • IC1 = NE555

  • Q1-Q4 = BC547

  • Q5-Q6 = PN2222

  • R1-R3, R8 = 100K

  • R4-R6 = 470R (ohm)

  • R7, R10 = 10K

  • R9 = 1K

  • R11, R12 = 220R (ohm)

  • R13 = 4.7K

  • C1 = 0.01uf, C2 = 100uf 15v

  • C3 = 2.2uf 15v

  • D1 = 1N4007

  • 6v-9v Relay

  • D1-D3 = LEDs

  • S1 = on/off switch

  • Battery 9v

Probe arrangement-

The probes can be arranged as shown in the diagram above. Insulated Aluminum wires can be used as the probes. The probes can be bind 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 maintenance in 1 or 2 month intervals.


  • Use 12Volt DC for operate the 9volt relay.

  • Use 9Volt DC for operate the 6volt relay.

  • The relay I used was a 9V/220ohm relay and that’s why the current limits resistor R12 was added in the circuit. If you use a 12V Relay, then the R12 can be shorted.

  • Do not use a relay that consumes 500mA. Maximum collector current PN2222 can handle is 600mA.

  • The load current, voltage ratings of the relay must be selected according to the ratings of the pump motor.

  • The type number of the transistors used here are not very critical and you can do suitable replacements if any type number is not available.