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, ¾
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.
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