Issue 138 January 2002
An RF-Controlled Irrigation System

Start • Controller/Receiver • Encoder/Decoder • The Firmware • Time's Up • Sources & PDF

When I sat down to write this article last fall, the leaves on the trees had not yet turned their autumn colors, but the beauty of the flowers in our garden beds was certainly on the wane. It was a dry summer, particularly punishing for farmers, and our gardens weren’t particularly splendid last year. Not that I didn’t try to keep them well watered, it’s just that it’s hard to beat a steady dose of rainwater.

We’re fortunate to have built a home on a large lake. Twelve years ago, we chose the lot based mainly on recreational concerns—swimming, canoeing, and such. I became seriously interested in gardening about five years back, and decided to install an irrigation system to make use of the unlimited supply of "free" water.

Our lot is about 25¢ above the lake’s level. As any mechanical engineer will tell you, it’s a lot easier to "push" water than it is to "pull" it, so I installed a 0.75-hp jet pump at the water’s edge. I decided against using a pressure tank and switch, as the water would be needed only when the pump was switched on, and the maximum continuous flow rate was desirable.

Because most of the rough landscaping had been done when the house was built, I decided it would be too much effort and expense to bury irrigation lines throughout the 0.75 acre of lawn and gardens that I have. Instead, I ran 1.5” plastic pipe on the surface, along the side border of my property. Six valves/garden hose fittings are spaced along the 400¢ length.

For a number of years, I was content to run down to the electrical panel in the basement to switch on the pump when I wanted to do some watering. Besides being inconvenient, occasionally I’d shut off the water valves when finished and then forget to return to the basement to turn off the pump. One year I damaged the pump by leaving it on for several days! Also I was getting lazy; I didn’t like the trouble of hooking up a hose, unraveling 100¢ of it into the desired position, attaching a sprinkler head, and then having to walk all of the way back to the other end to turn on the water valve.

I decided what I needed was a controller that allows me to program specific watering times and durations. Units like this are commercially available, of course, but I also wanted to be able to control the water using a small keyfob transmitter while I puttered around in the gardens.

In my last article, I described a wireless MP3 player, which used low-cost UHF transmitter/receiver modules from Abacom Technologies ("Listen Everywhere," Circuit Cellar 134). I was pleased with their performance and technical support from Abacom, so I decided to check out Abacom’s products again.

Photo 1—Here’s the actual controller/receiver sitting in my family room. Just visible in the background is a glimpse of the lake—the source of water for the gardens. Not visible is the AC adapter used for power, or the power relay, which is located at the electrical panel in the basement.

I wanted the transmitter to fit in a keyfob, so I chose the AT-MT1-418 AM transmitter module, which is about the size of a penny. I also chose Abacom’s keyfob transmitter case, which comes in various switch cutout configurations.

I decided to use a sensitive receiver because I anticipated a low transmitted signal level given such a small transmitter. The QMR1 Quasi AM/FM superhet receiver module fit my needs. I particularly like this module because its 1-square-inch SIP mounts easily on a circuit board by pins on 0.1” centers. I like one-stop shopping, so of course I was pleased to be able to get Holtek encoder/ decoder chips from Abacom, as well. I’ll describe the chips in more detail later in the article.