DN Staff

March 15, 2004

3 Min Read
Rainman John Has a Natural Moisturizer and an Excellent Duck

Seeing lawn spinklers constantly running in the rain, John thought about how silly and wasteful they are. So he developed a device that monitors the moisture content of the soil and automatically triggers a sprinkler system when required. The sensor is a pair of electrodes (based on bicycle spokes), while the controller for the device is based on a fluid detector powered by the nominal 24V ac most sprinkler systems use.

Water minder parts list

Amt

Part Description

Allied Part #

1

Relay, 24V dc

821-2212

1

Switch, SPDT Toggle

676-3000

1

Box Plastic

736-0063

1

Trim Pot, 50k

754-3212

1

2N3906 Transistor

950-3002

1

LED, Red, T1, .75

749-9819

1

Zener Diode, 24V dc

950-6043

2

Diode, 1N4001

266-0001

1

Cap, Elec, 220 mF/50V

852-7082

1

Resistor, 270V, 1W

296-6508

Additional parts required: Fluid detector, miscellaneous resistors and capacitors, and bicycle spokes


Additional information:

The LM1830 has a built-in oscillator, a comparator and output drive circuitry. When the sensed pin has a higher resistance (drier) than the reference, the output turns on. In this case the output cannot supply sufficient drive current for the signal LED and relay, so a transistor buffer is added. The dryness setpoint is set by the trimpot and a bypass switch is included for testing, etc. The relay specified can handle 10 amps - plenty for a water solenoid.

The sensor is a pair of electrodes that contact the soil at the desired level. They should be stainless steel to resist corrosion. Where's the best (cheapest) place to get these - bicycle spokes! I potted 2 of them in a 35mm film canister and put heatshrink on all but the lowest 1" of the spokes.

Camera ready artwork for the pcb and chassis cover are available from:

Sunspot Svcs,
115 Greenbrier Dr
Simpsonville, SC 29680 $2, check or money order plus S.A.S.E.

PDF diagram

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