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
Allied Part #
Relay, 24V dc
Switch, SPDT Toggle
Trim Pot, 50k
LED, Red, T1, ¾
Zener Diode, 24V dc
Cap, Elec, 220 mF/50V
Resistor, 270V, 1W
Additional parts required: Fluid detector, miscellaneous resistors and capacitors, and bicycle spokes
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.
Wearable cameras possess the power to alter our work lives, the way industrial enterprises operate, and our personal lives because of the insights they can bring from their unobtrusive, first-person point of view.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.