Finding a buried wire

Dave Hein

I have been trying for months·to locate a lawn sprinkler valve buried somewhere in my front yard.· I have spent a lot of time poking around the front yard with a metal rod to try to hit the valve cover, but I was unable to find it using this method.· I knew about the technique of sending an RF signal on the wire that runs from the control box to the valve, so I tried a transmitter I have that operates at around 403 MHz.· However, this frequency is way to high to get through the ground, so that attempt didn't work.

After doing some internet research, I realized I needed a transmitter that operates in the AM band.· I thought of running out to Radio Shack or Frys to see what they had, but then I realized that the AM band is well within the capabilites of the SX.· I programmed an SX28 in an SX Tech board to generate a signal within the AM band frequency range.··The RF signal is modulated by a square wave at 1/500th the RF frequency to produce a tone.· Basically, I send out 250 cycles of the RF signal, and then zeros for the next 250 cycles.

I was able to receive the signal on an AM radio at around 850 KHz, which would make the modulated tone around 1.7 KHz.· I connected the output pin of the SX to one end of the controller wire, and I listened for the signal in my front yard using a small AM radio.· I followed the direction where the signal was the strongest, and I found the sprinkler valve in a matter of minutes!

To me, this demonstrates the versatility of the SX chip.· I've used the SX to do timers and other simple cirucits, but I've also used it to read a gyro chip and control the direction of a rocket.

The code for the AM radio tone generator is attached below.

Dave

Shawn Lowe

Wow dave, that is freakin cool! Thanks for sharing. I would have never thought you could do this with an SX.

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Shawn Lowe


When all else fails.....procrastinate!

Leon

A former colleague of mine used a 555 timer to create a signal for a perimeter wire for a robotic lawn mower he was designing. I think the frequency was 500 kHz. He didn't have any problems detecting the signal with some simple hardware connected to a PIC.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Dave Hein

I found from my internet search that this is the technique used for invisible fences for dogs.· It was pretty cool following the signal in the ground.· I was wearing a pair of headphones that pick up AM/FM radio.· As I walked around my front yard it was almost as if I was hearing the sound coming directly out of the ground.· If I got down on my hands and knees I could hear the sound become much louder and clearer as I got closer to the buried wire.

I didn't want to crawl all over my front yard, so I switched to a small AM radio hanging down from the earbud wires.· It worked very well.

It was kind of funny when my wife saw me working on the computer while I was programming the·SX.· She asked me why I wasn't working on the sprinkler system.· I told her I was working on the sprinkler system.· She left with a disbelieving look on her face.

Dave

Shawn Lowe

That's great! I'll have to remeber this so I can look like a "super tech" to my friends and family if we need to do something similar.

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Shawn Lowe


When all else fails.....procrastinate!

Post Edited (Shawn Lowe) : 7/29/2009 9:25:26 PM GMT

RickB

An unbelievably complex version of this concept is in the newest issue of Circuit Cellar. Would you believe 2 DSPICS to do the same thing? I must be blind, because I fail to see why the complexity is needed.

Dave Hein

I suspect the more complex implementation in the Circuit Cellar does lots of filtering to reduce harmonics.· In my quick and dirty implementation I produced lots of harmonics.· I was able to pick up the signal at the fundamental frequency of 850 KHz, but I also picked it up at the high end of the AM band at 1700 KHz.· Not only that, but I picked it up some of the upper harmonics on the FM band as well.· However, the signal was very low power, and I was not able to receive it at a distance of 50 feet from the buried wire.

I'll have to take a look at the latest issue of the Circuit Cellar to see how they implemented it.

Dave