I know this is already a technology that exists on some level (ELECTRONIC DOG DOORS) but i think it would be a cool project to learn some things. So what technology exists that can be read from a dog collar from 1-2 feet away? I know some passive RFID systems will work at this range, and i love that the no battery would be required on the collar, but i do know that with increased range in passive systems requires increased power and sensing on the receiver. So that may be a financial limitation. I would like to keep this a cheap project, if at all possible.
Other technologies i am considering but need more information about;
RFID (active and passive)
Bluetooth
Ultrasonic
Strobing infrared led (not sure if really possible)
Depends how secure you want it.
You could use a tuned circuit in/near the door that works like a metal detector to detect a metal collar on the dog.
Of course, any piece of metal will unlock it, so it won't be very secure.
Ideally i would like to be a little more secure, as you pointed out, any dog with a metal tag would likely be let in. Would be nice to have some kind of ID associated with it.
A small but powerful magnet can fairly easily be detected and would be a bit more selective than a metal tag.
For example, a coil of wire with lots of turns will generate a small but easily detectable voltage as the magnet moves. The bigger the coil and the more turns, the better. For example, you could frame the dog door with the coil.
Another option would be to use a magnetometer (electronic compass chip) like this one. That will detect a magnet, moving or not, several feet away. You simply look for a change in the direction of "magnetic North".
Wow that adds a level of creativity I would have never even thought of googling haha. Thanks!
Would it be possible to use two different strength magnets so the door could distinguish between two dogs? One that's allowed in and out and one that isn't at certain times (which could then be programmed by arduino for a schedule)? I would imagine the magnetometer would detect a pretty consistent range assuming the dog approaches the door at a similar path, but it might be a little confusing if both are trying to enter at once. Could just exclude both readings together, as a workaround...
jremington:
Another option would be to use a magnetometer (electronic compass chip) like this one. That will detect a magnet, moving or not, several feet away. You simply look for a change in the direction of "magnetic North".
Very clever idea, jremington.
I was originally thinking of Hall effect detectors, but they won't operate at the range he requires.
I'm glad you think it is a good idea, because the sensitivity of magnetometers to nearby iron, magnets or current carrying wires is usually considered a real pain in the *ss!
I use the HMC6352 2D magnetometer as a "visitor arrival sensor" in our very long driveway. It can easily detect an automobile passing 3 meters from the sensor and the maximum range is likely more than twice that distance.
jremington:
I'm glad you think it is a good idea, because the sensitivity of magnetometers to nearby iron, magnets or current carrying wires is usually considered a real pain in the *ss!
I use the HMC6352 2D magnetometer as a "visitor arrival sensor" in our very long driveway. It can easily detect an automobile passing 3 meters from the sensor and the maximum range is likely more than twice that distance.
A car is a large chunk of steel, containing several magnets and many current carrying wires.
Hopefully, the attachment to the dog collar will be somewhat smaller.
