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Inductive Guidance

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By dallaby

May 28, 2010
dallaby's picture

       I am trying to build a robot lawnmower(yes another guy trying this).. I need to understand Inductive guidance or RF technology a bit better to build a buried wire circuit for this.. I have read alot on the web and am starting to understand inductor/capacitor circuits.. I built a transmitter using a 555 and a 2n2222 to raise the current in the wire.. I then built a L/C circuit with a 339 comparator and I can tune it to pick up the signal from the wire(I can see this on my oscilliscope)..

        My question is that I seem to have alot of noise as well and even if I touch the inductor I see alot of noise from that as well.. Is there an electronic way to filter this out? Did I make my circuit wrong? Is there a better way to accomplish what I am trying??(maybe using am radio signal in the wire instead of RF)??  Please any information on this topic would be greatly appreciated as I have invested ALOT of time and money trying to solve this issue..

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By Salvage
@ Wed, 2010-06-02 02:32
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The third link with the schematics is a dead link.

By dallaby
@ Wed, 2010-06-02 02:48
dallaby's picture

   Here is the main link..

http://www.robotshop.se/micro/wwwrc_us/indext.htm

For the schematics click on diary on the front page then scroll down to the midway point .... It is not so much a schematic as a concept drawing though..

By Salvage
@ Thu, 2010-06-03 03:31
Salvage's picture

In looking at the schematic and reading his description, it is not RF, it's 38kc. So, basically, it's still an inductive loop design with a range of only 50cm.

By dallaby
@ Fri, 2010-06-04 00:11
dallaby's picture

   I thought you told me that for it to be an inductive loop it would have to have multiple turns?? Now I am confused..Does it have to be a certain frequency to be RF?

By Salvage
@ Fri, 2010-06-04 02:16
Salvage's picture

I said the more turns you have, the stronger the field and the better the signal to noise ratio.

Normally, anything over 100kc is considered RF, though at that frequency the circuitry looks more like audio than RF.

By dallaby
@ Fri, 2010-06-04 04:47
dallaby's picture

    First of all what do you think of that circuit/system? Will it work properly (in your opinion)?

    Oh ok.. that makes sense... So if it is running at 38khz and I were to use your other suggestion about multicolor wire that would increase the signal strength right?

    I presume the capacitors that he has marked with an * are the same value, and I can calculate the values from an online L\C calculator correct?

   One other thing can the signal strength on this circuit be increased by any other means? (ie incease voltage or current in buried wire)

 

 

By dallaby
@ Sun, 2010-05-30 05:34
dallaby's picture

   Hey Salvage , I really appreciate the info you provided.. I will be honest I am an extreme beginner when it comes to electronics but the good news is I can read, hehehe... So I am taking the info you posted and going to google to try and comprehend it all a bit better.. If possible could you draw me a schematic putting it all together... Thanks again for the help so far..

By Chris the Carpenter
@ Sat, 2010-05-29 02:57
Chris the Carpenter's picture

I have to say that was one of the best answers to any question I have ever seen around here. The information density in what you have written above is staggering.

Well done.

By Salvage
@ Sat, 2010-05-29 16:05
Salvage's picture

Chris,

That is high praise coming from you and I appreciate it.

I've written a number of articles for our on-line robotics club, http://robojrr.tripod.com/ you might want to check out. The information is somewhat dated now but still good stuff. Our series on basic electronics is especially good.

By Salvage
@ Sat, 2010-05-29 00:48
Salvage's picture

Inductive loop systems have been around for many years and they are pretty simple. For a long time they were used in churches for the hard of hearing. A simple coil, (just a few turns), went around the church. An audio amplifier, (5 watts is sufficient), is used to drive the inductive loop with the program material.

Small receivers were given out to people needing the "extra volume". The receiver was nothing more than a small audio amplifier with an inductive loop as the input. Ideally, you need to have some active filtering, on the input to limit the frequency response to 500-5,000hz, otherwise, the 60hz all around us will make the units unusable.

For your application I would shoot for an oscillator at about 5-10Kc and about 5 watts of drive. Use some multiconductor wire for your loop and cross-connect unlike colors at the open ends so you have multiple turns. The receiver can be most any loop of wire, (experiment for best S/N ratio), feeding an op-amp for gain, an active notch filter, and then drive a PLL like the LM567 tuned for whatever frequency you're using. You may want to make a "sensor deck" with 3 or more sets of sensors for proximity detection of the sense cable. You should be able to build the whole system for under $20.00.

Hope this has been of some help and good luck with your project..

 

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