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||Trim Pot, 50k||754-3212|
|1||LED, Red, T1, .75||749-9819|
|1||Zener Diode, 24V dc||950-6043|
|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|
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:
115 Greenbrier Dr
Simpsonville, SC 29680 $2, check or money order plus S.A.S.E.