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Water Level Sensing and Control
by Tony van Roon, CET
This is a simple but reliable circuit for your sump-pump, aquarium, boat, or whatever. Please be careful when working with 115Volt line voltage!

Water level sensing schematic

Parts List
R1 = 10 ohm, 10 watt, wirewound
R2 = 100 ohm, potentiometer, wirewound
R3 = 1 Mega-ohm potentiometer
T1 = Transformer, 12.6volt, 1.2amp (min)
SCR1 = Silicon Controlled Rectifier, C106Y1, or equivalent
TR1 = TRIAC, SC141D, rated 6 to 10 amp at 200 to 400 volt. Case TO-220

A Couple Notes
Triac TR1 enegizes a load which might control a valve, indicator light, audible alarm, relais, etc. The SC141D can be substituted with NTE5635, or Radio Shack 276-1001 model.
When the water-level is "low", the probe is out of the water and SCR1 (C106Y1) is triggered "on". It conducts and imposes a heavy load on Transformer T1's secundary winding. That load is reflected back into the primary, gating TR1 on which energizes the load. The C106Y1 can be substituted with a NTE5452 or Radio Shack (or Tandy) 276-1352
Applications of the circuit are limited only by one's imagination.
The load may vary from a watervalve, a relay controlling a pump, etc. Lots of possibilities.
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Copyright © Tony van Roon, CET