gbell@sdcc13.ucsd.edu (Greg Bell) (03/24/91)
I need some ideas on an arm/disarm method for an auto alarm I'm designing for fun (80% built, actually). Here are the possibilities I've come up with along with their disadvantages. Does anybody have any idea how to overcome the disadvantages and/or any new possibilities? 1) One of those pre-made RF transmitter/receiver pair you can buy. I've heard of thieves using "scanners" to scan through all the possible digital codes. Also, what happens when the batteries die? You need two ways to arm/disarm with this setup. 2) A keypad mounted on the center console. The only problem with this is that if somebody breaks in and hacks the thing to pieces trying to shut the alarm off, I have no way of disarming the system when I get back! 3) A magnet sensor positioned somewhere "secret". But all somebody has to do to defeat this is watch me arm the system. 4) An IR transmitter/receiver pair. I've actually already built the transmitter onto a tiny board. But, again the problem with the batteries. Also I can't find a case small enough to house the thing. Many thanks for any ideas! -- ----------------------------------------------------------------------------- Who: Greg Bell Address: gbell@ucsd What: EE hobbyist and major Where: UC San Diego -----------------------------------------------------------------------------
davem@hp-lsd.COS.HP.COM (Dave K. Martin) (03/27/91)
Wayyyy back when, I recall having seen a Popular Electronics article on a key- less lock. It was in the early 70's I think but am not sure. Anyway, the article described a small oscillator and a receiver mounted on a small board. The 'key' was a small plastic cube with a pickup coil and an oscillator. The pickup coil would pick up enough RF to power the osillator in the 'key'. When the receiver picked up the apropriate frequency (and probably modulation), it would toggle the state of the output. To unlock, the key just has to be held close (2-3 inches?) from the transmitter receiver pair. All in all, a pretty elegant little design. Virtually pickproof and no batteries in the remote to worry about. I may still have the P-E issue somewhere. If you want to follow up on this approach, email me and I'll see if I can find it.