project lawnmover

Discussion in 'The Projects Forum' started by wretan, Apr 16, 2009.

  1. wretan

    Thread Starter New Member

    Mar 18, 2009
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    Hello!

    Is there anyone that have any idea how to build a simple "Buried Wire Fence"?

    I am searching for a the simpliest way how to get a relay to switch on/off on the mover when the it strikes over the buried cable? :confused:
    I suppose it in some way consist of a 555-timer to produce a frequency in the cable and maybe a "coil+capacitor+amplifier" in the mover to read the signal? I´m a bit confused

    Is there anyone that have any ideas about this? Who should I send a bottle of wine for any useful tip?

    Regards
    Wretan
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    If it were me, I would buy an off-the-shelf invisible pet fence and hack the collar module to drive a relay.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I agree with thingmaker. Due to weather conditions, and transmission line calculations, it would be simpler.

    The theory is the buried "antenna" is akin to the remote control switch on a dog training collar, but with only about a 4 foot "range", and it is transmitted around the periphery of your property. The color is a receiver tuned to the signal that antenna produces, and when it is received, it engages.

    Some dogs I know, mostly larger breeds, figure out if they just run really fast, they stumble out the other side anyway. Hopefully the mower doesn't attain AI.
     
    Last edited: Apr 16, 2009
  4. wretan

    Thread Starter New Member

    Mar 18, 2009
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    Hello and thanx for the replies!

    Unfortunately its illeagal in my country to buy and having a invisible pet-fence.

    Another thing we have that could be useful (how?) is a detector för cables in the wall, this could work but they are only reacting on AC-current 230 volts :eek: doesn´t feel nice to have that in my garden

    Any other ideas?

    /Wretan
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
    Hello,

    I do not know how sensitive metaldetectors can be.
    Otherwise you could use a metaldetector to look for the burried wire,

    Here is a link to some metaldetectors:
    http://www3.telus.net/chemelec/Projects/Projects.htm
    The metaldetectors and design of coils for them are about halfway the page.

    Greetings,
    Bertus
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Is the purpose for the mower to navigate around the buried wire, or to kill the engine WHEN a power line is hit?
     
  7. wretan

    Thread Starter New Member

    Mar 18, 2009
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    0
    hello!

    the purpose with the detection of the wire is to reverse one motor so that the mover will turn, a pretty simple way to get a random pattern of lawn cutting i think.

    Isnt there any way of detecting cables? how do telephone-companies find out where the lines are? I have heard about a system that they use but it sounds a bit simple, probably a frequency that´s picked up by a reciever (like a regular AM-reciever?) :)

    I´m sick of cutting my lawn, ok - I´m lazy :)
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
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    Phone companies use either an inductive amplifier (if the lines are good) or a metal detector (if the lines are bad.) Phone companies also keep very accurate maps.
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    You could set up a 4" high wall around the yard, rewire a roomba vacuum, strap an engine and blade on it, and let it loose. :D
     
  10. italo

    New Member

    Nov 20, 2005
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    burried indeed why not infrared. no wires
     
  11. wretan

    Thread Starter New Member

    Mar 18, 2009
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    Hello guys och tnx for the reply! :)

    I think I will go for the inductive amplifier system, google is my friend!

    Does anyone maybe have any ideas how to build a cable detector, I suppose that telephonecompanies used a tone-generator in the end of the cable, but how do they listen to the signal in the wire?

    A Coil amplified with an amplifier should of course do this, but how do I control that the coil only "hear" this signal and not all other signals in the surroundings?

    Thanx!
    /Wretan
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    The phone co marked all of the drops along a 50 pr. cable [to be replaced] . Every drop was cut, just missed 'em by about 2 ft.
    I used tone in cable & portable amp for cable break/ short detection, range verry short, inch or two, mostll direct contact. Power prob. 1/2 W @ 1 kHz. Maybe more power higher freq. more gain in amp. might work.
    What happens if inertia carries mower over line, now confusion sets in , " which yard am i in "
     
  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Just a few thoughts from past: In 1960 I made a remote garage door opener with a noise generator, relay wired as freerunning oscillator connicted to a loop ant under running board. Receiver another loop under concrete driveway, tied to a gas triode tube. Main point, range was obout two feet , low false operations. Cable fault test portable amplifier used a bridged "T" filter in feed-back three transistor [ CK722] amplifier, should still work but use OP amps, " T" , rectifier, & relay driver. Burried cable might be direct burial 9 pr telephane cable. combine pairs to single wire, connect beginnings to ends to make 9 turn loop. Best operatin frequency ???. Good luck.
     
  14. yourownfree

    Active Member

    Jul 16, 2008
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    you can make a loop, so the the wire starts at one point, goes around your yard and ends at the same point. Hook that to an audio amplifier speaker terminal without the speaker attached. Calculate the wire by using the correct guage of wire that will be closes to 4-16 ohms. I know speakers are in impedance so I dont need corrected here, what we are doing is looking for a reasonable load for the amplifier to work into. Dont try it unless you can physically check and see at least 4 ohm on the digital ohmmeter. attach a tone generator to the input of the amp. crank it up 1/2 way or so to allow for ample output. For the receiver all you would need is a pickup coil and a good audio preamp and tone selective. That way nothing but the proper tone will set it off. then place a squelch circuit in it that you can adjust for distance.
    even can use a dtmf encoder generator which are cheap and decode it at the lawnmower with dtmf chip. That way there is no mistake about the tone. You csan test it out first with a headphone attached to the circuit so you can hear it for yourself. either that or stick a pole in the center of your yard and attach the lawnmower to it with a rope. as it goes round and round it winds itself up and gets closer to pole until it the tension of the mower tugging and pulling trips the kill switch. Ok thats stupid. But seriously using dtmf you could use the telephone pad to tell your lawnmower to back up, stop,go, or whatever you want it to do. You could even put a transmitter at the lawnmower end to respond back to the master control at the house and tell it when it has reached the wire, so it can get a new command, whatever that might be. anyhow you get the idea with this method. Guess you could put two coils on mower to know if the second coil is activated then you are now in your neighbors yard or running free down the street.
     
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