Description
Notes
By means of a Relay, employed to drive a water pump, this circuit
provides automatic level control of a water reservoir or well. The
shorter steel rod is the "water high" sensor, whereas the longer is the
"water low" sensor. When the water level is below both sensors, IC1C
output (pin #10) is low; if the water becomes in contact with the longer
sensor the output remains low until the shorter sensor is reached. At
this point IC1C output goes high, Q1 conducts, the Relay is energized
and the pump starts operating.
Now, the water level begins to decrease and the shorter sensor will
be no longer in contact with the water, but IC1C output will be hold
high by the signal return to pin #5 of IC1B, so the pump will continue
its operation. But when the water level falls below the longer sensor,
IC1C output goes low and the pump will stop. SW1 is optional and was
added to provide reverse operation. Switching SW1 in order to connect R3
to pin #11 of IC1D, the pump will operate when the reservoir is nearly
empty and will stop when the reservoir is full. In this case, the pump
will be used to fill the reservoir and not to empty it as in the default
operating mode.
Circuit Diagram:
Parts:Circuit Diagram:
- R1 = 15K - 1/4W Resistors
- R2 = 15K - 1/4W Resistors
- R3 = 10K - 1/4W Resistor
- R4 = 1K - 1/4W Resistor
- D1 = LED - any type and color
- D2 = 1N4148 - 75V 150mA Diode
- Q1 = BC337 - 45V 800mA NPN Transistor
- IC1 = 4001 Quad 2 Input NOR Gate CMos IC
- SW = SPDT Toggle or Slide Switch (Optional)
- RL1 = Relay with SPDT 2A @ 230V switch
- Coil Voltage 12V - Coil resistance 200-300 Ohm
- Two steel rods of appropriate length
- The two steel rods must be supported by a small insulated (wooden or plastic) board.
- The circuit can be used also with non-metal tanks, provided a third steel rod having about the same height of the tank will be added and connected to the circuit's negative ground.
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