Here is a link for a (old)patent on a vehicle in lane detector using passive coils in the roadway. No circuit details but it sounds like what Dan was talking about. 12 inch single turn coils in the road with a 100nF cap in series. etc. The hard part of this project is figuring out what the search description should be.
http://books.google.co.in/patents/US5708427 Tim Laing > I don't think anyone has suggested a simple 'tag' which consists of just > a coil with a diode in series. Could be a loop with detector, such as > some of the cheapest RFID tags use. The interrogator is something > driving a large coil [in this case just around the openint] and > detecting the second harmonic generated by current flowing in the > diode. I think it could be very simple but not proposing a design. > > Ed > > danial stocks wrote: > >> >> >> If you want to do something simpler, you could try a passive resonance >> absorber - this is how some of those anti theft things in shops work - >> have an oscillator sweeping a small frequency range - the tag on the >> cat is a resonant LC circuit. When it is near the search coil, there >> is a dip in te spectrum - basically the same idea as a grid dip meter. >> This might be more sensitive than just a shorted loop. The oscillator >> sweep will give immunity to random objects - something like a shorted >> loop will absorb across the whole range - the sweep is wide enough >> that thermal variations etc in the resonant circuit are accounted for >> - youare just looking for an absorption dip anywhere in the range. >> Shop sensors typically do this in the 6-8mhz range. >> Dan >> >> > >> > I work with RFID tags at work all the time, I hate those little >> buggers, >> > half the time they don't want to read on the pallets. Knowing the >> typical >> > cat I will have to be replacing them all the time. I think if I can >> get a >> > simple circuit to detect a shorted loop about 1.5-2 inches in diameter >> I >> > will be pretty well set. I just want to throw something together with >> > parts I have on hand. The RFID is a good idea though, thank you for >> > suggesting it. >> > Tim Laing >> > > >> > > get an RFID reader. some RFID dev boards can be had for pretty >> cheap. Put >> > > the tag on the cat, door opens for the cat with the tag... >> > > Dan >> > > >> > >> >> > >> Hi, this is off topic but I know there are a lot of electronics >> guys >> > >> here. >> > >> I posted this on Neonixie-L first. I also thought I would post >> here as >> > >> well. This cat door is for the black cat that was guarding my CRA >> > >> skysweeper tube! I guess a automatic cat door would be on topic if >> I >> > >> used >> > >> tubes. The tubes could sit under his cat bed and keep him warm. But >> I >> > >> think that transistors or an IC or two would be more practical. >> Thanks >> > >> guys. >> > >> Tim Laing >> > >> >> > >> ---------------------------- Original Message >> > >> ---------------------------- >> > >> Subject: Off topic Circuit for automatic cat door. >> > >> From: lai...@wcoil.com >> > >> Date: Thu, December 20, 2012 3:04 am >> > >> To: neonixie-l@googlegroups.com >> > >> Cc: lai...@wcoil.com >> > >> >> -------------------------------------------------------------------------- >> > >> >> > >> There are a lot of smart people on this group so I thought I >> would ask >> > >> for >> > >> some help. We have a stray cat that we have adopted. He is an >> indoor >> > >> outdoor type of cat. My personal experience is if they started >> outdoors >> > >> they are very unhappy if you try to keep them in all the time. >> Well the >> > >> problem is there are some other strays that beat up on him and get >> at >> > >> his >> > >> food. My temporary solution was to leave the window to our stair >> landing >> > >> open and Skink could jump up about 5 feet and get in through the >> window. >> > >> Then he could sleep on the landing if we were not home and eat as >> well. >> > >> Well we have two problems, 1) it is now pretty cold(The stairs >> lead to >> > >> our >> > >> front door so that area is not heated.) 2) The big problem is I >> came in >> > >> tonight and the wild stray that has been going after Skink had him >> > >> cornered on the landing. Needless to say I wasn't too happy, the >> last >> > >> thing I need is a tom spraying on the landing! And no, I am not >> going >> > >> to >> > >> shoot the other cat as I live in town and I don't shoot cats etc. >> > >> My idea was to make a automatic cat door that would open for only >> one >> > >> cat. I was thinking that if I made a cat collar out of light gauge >> > >> copper wire with male and female spade connectors this would form a >> > >> single turn shorted loop. (The wire would be light gauge so if he >> got >> > >> caught the wire would break.) The cat door would be a partly >> formed with >> > >> a square wood tube that the cat would enter with a solinoid >> latched door >> > >> at one end. On the outside of the wood cat tunnel I would wind some >> > >> turns of copper wire that would be tied into an oscillator >> circuit. The >> > >> shorted turn would either kill the oscillator or shift its >> frequency >> > >> allowing the door to open. >> > >> I can build just about anything electronic or mechanical and have >> lots >> > >> of parts on hand but I am not very skilled on scratch designed >> circuits >> > >> like this. Would somebody here be willing to help me with some >> pointers. >> > >> I can work from an hand drawn schematic. I should be able to supply >> > >> power from a wall wort if needed. >> > >> Thanks >> > >> Tim Laing >> > >> >> > >> >> > >> >> > >> >> > >> >> > >> ------------------------------------ >> > >> >> > >> Visit the TCA web page at: http://www.tubecollectors.org >> > >> >> > >> If you have questions about or problems with >> > >> the TCA reflector, please contact the list manager >> > >> Ron Lawrence directly at W4RON at carolina dot rr dot com >> > >> >> > >> Visit the TCA Tube Photo Gallery web page at: >> > >> http://radioheaven.homestead.com/TCA.html >> > >> >> > >> >> > >> >> > >> Yahoo! Groups Links >> > >> >> > >> >> > >> >> > > >> > >> > >> > >> > >> > ------------------------------------ >> > >> > Visit the TCA web page at: http://www.tubecollectors.org >> > >> > If you have questions about or problems with >> > the TCA reflector, please contact the list manager >> > Ron Lawrence directly at W4RON at carolina dot rr dot com >> > >> > Visit the TCA Tube Photo Gallery web page at: >> > http://radioheaven.homestead.com/TCA.html >> > >> > >> > >> > Yahoo! Groups Links >> > >> > >> > >> > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
