RSS Feeds
Rainman John Has a Natural Moisturizer and an Excellent Duck
By Design News Staff -- Design News, March 14, 2004
|
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.
