The water level controller circuit is built around IC 555 (IC2) to monitor the water level in the overhead tank and ‘on’/‘off’ status of the motor through the inverter and driver circuits. The transistor switch circuitry monitors the flow of water and raises an alarm if the pump runs dry.
Water level controller circuit
Power supply is obtained through step-down transformer X1, diodes D1 through D4, capacitor C1, series current-limiting resistor R1, regulator IC1, and noise-filtering capacitors C2 and C3. The set-up for the water-level sensing electrodes is shown in Fig. 2. Electrodes are suspended into the tank such that they don’t touch each other. Points B, L and U of the water level controller circuit are connected to the respective points of the sensor electrodes assembly.
When water in the tank is below the lowest level L1, all the electrodes are electrically separated and hence points L and U (pins 6 and 2 of IC2, respectively) are pulled up to the supply voltage through resistors R2 and R3, respectively. Therefore, to reset IC2 the output of IC2 at pin 3 goes low. As a result, transistor T1 stops conducting to drive transistor T2 and relay RL1 energises. The motor pump now starts running to fill the tank with water. Freewheeling diode D5 prevents chattering of the relay due to the back emf produced by the relay coil.
When the water level rises to bridge the electrodes, because of the conductivity of water, pin 6 (E1) is pulled down to ground (E2). This does not alter the output state of IC2, which maintains its previous state, and the motor keeps running. When water rises to the overflow level L2 and touches electrode E3, point U (pin 2 of IC2) is connected to already sunken ground electrode E2, thereby triggering it. IC2 resets to give a high output at pin 3. This is inverted by transistor T1 to cut off transistor T2 and de-energise relay RL1. The motor pump now stops to prevent water overflow.
Water level falling below level
As water is consumed, the water level comes down leaving electrode E3 isolated from ground electrode E2. Now point U (pin 2 of IC2) is pulled up to the supply voltage. This does not change the output state of IC2 and the motor remains switched off.
When water level again falls below electrode E2, IC2 resets to cut off transistor T1. Transistor T2 conducts to energise relay RL1 and the motor is powered to run. This is how the process continues. LED1 glows whenever the relay energises, indicating that the motor pump is running.
As the values of resistors R2 and R3 are very high, corrosion of electrodes is very little. Capacitors C2 through C7 filter out unwanted noise. Switches S2 and S3 can be used to manually switch on and off the motor pump, respectively, when water is in between the upper and lower levels. Switch S1 is used to disable the unit during dry pump run or while flushing the tank.
Water level controller: In-tank setup
For the sensor electrodes, use a moulded-type AC chord (used for tape recorders) with its pair of wires sleeved at the end and connected together to form the electrode. Other electrodes can be made similarly. These three AC chords are suspended inside the tank from a longitudinally cut PVC pipe (used for electrical wiring).
The arrangement for the dry pump sensor is shown in Fig. 3. A moulded-type AC chord with its pair of wires sleeved at the end can be attached firmly to the delivery pipe such that water falls onto the plug leads. The sleeved ends are connected to points A and B of the water-level controller circuit.