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Monday, April 6, 2009

Water Detector With Sump/Bilge Pump Controller

This moisture detector with pump controller is built around the special purpose LM1830 IC. The LM1830 is designed to detect moisture by passing an AC current through a set of probes. An internal comparator compares the resistance of the probes to an internal reference. When the resistance between the probes is low (indicating the presence of water or other conductive liquid) then the IC triggers it's output. An AC signal avoids electroplating and corrosion problems that are common when DC is used. To provide an adjustable delay hysteresis to avoid cycling the pump, a timer based around the 555 is used a range of about 5 seconds to two minutes. In this way the pump will stay active for a set amount of time even if the fluid level is below that of the probes.


  • R1 ------ 1 470 Ohm 1/4 W Resistor
  • R2, R4 ---- 1 10K 1/4 W Resistor
  • R3 ------- 1 6.8K 1/4 W Resistor
  • R5 ------- 1 1 Meg Linear Taper Pot
  • R6 ------- 1 51K 1/4 W Resistor
  • C1 ------- 1 470uF 35V Electrolytic Capacitor
  • C2 ------- 1 0.001uF Ceramic Disc Capacitor
  • C3 ------- 1 0.05 uF Ceramic Disc Capacitor
  • C4 ------- 1 20uF 35V Electrolytic Capacitor
  • C5 ------- 1 6.8uF 35V Electrolytic Capacitor
  • C6, C8 ---- 2 0.01uF Ceramic Disc Capacitor
  • C7 ------- 1 100uF 35V Electrolytic Capacitor
  • U1 ------- 1 LM1830 Fluid Detection IC
  • U2 ------- 1 555 Timer
  • Q1 ------- 1 2N5305 NPN Power Transistor
  • D1, D2 ---- 2 1N4148 Signal Diode
  • D3 ------ 1 1N4002 Rectifier Diode
  • K1 ------- 1 Relay With 12V Coil (See Notes)
  • S1 ------- 1 SPST Switch
  • PROBES ---- 1 Stainless Steel Probes (See Notes)
  • MISC ----- 1 Case, Knob, Board, Wire, Sockets For U1 and U2


  • The probes should be made of stainless steel and mounted in a non-conductive fixture. Stainless steel nails, bolts or welding rod will make ideal probes. Good non-conductive materials are Lexan, plexiglass or plastic. The probes are to be placed at the liquid level at which you wish the pump to turn on.
  • K1 should be chosen according to the requirements of the pump. If you are running a 12V pump then common automotive relays will work fine. If you are running a mains powered pump then you will need to make sure the contacts are rated accordingly.
  • S1 provides a manual pump switch.
  • R5 adjusts the on-time of the pump once moisture has been detected. It is adjustable from approximately 5 seconds to approximately 2 minutes.
  • The probes should be cleaned periodically to assure reliable operation.

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