Build Your Own Electronic Key Card Lock 168
edBX writes "GideonTech.com has a new guide up on how to make your own electronic lock using a key card. Built using a phototransistor, infrared-emitting diode and a few ICs, they are able to turn on their computer using a punched out phone card."
Just a thought... (Score:5, Interesting)
DIY Lock (Score:2, Interesting)
My trick was I found some old optical card scanners which would read the bar-codes printed onto credit-card sized plastic cards. Then I found the local gamery in the mall was using compatible cards, each coded with a different 24-digit number, being passed around to enable the various games as long as there was sufficient funds on account to the number of the card. Neat! I picked several "spent" cards out of the trash can, and went home and read them on my system, then programmed a few little AVR chips to recognize those specific cards. I keep one in my wallet to control the secure/access mode to my house alarm system and car. If it gets lost, its not obvious at all that the card has an alternate use. In the event I want some more cards, add or delete which cards work with the AVR, its not hard to put them back in the programmer and reflash their ROM with the new code list.
Actually, on mine, I never decoded the bar-code digits, I only kept track of whether it was a fat/narrow stripe and fat/narrow space by examining a counter interrupted on each rising and falling edge, and storing the counter state in an array. Upon scan completion, I examine the array and reduce it to 64 bits worth of fat/narrow of the first 32 stripes / spaces I encounter. There is a little start pattern at the beginning that helps a lot to align the data field so you are not shifted a bit or two off. To be on the side of possible error, I allow 8 bits to be bad before I declare the card invalid. This was from trial and error, as I could generate bad reads by not moving the card just right through the reader. I usually got at least one bit that wasn't right every time I scanned. I never did get it working absolutely perfectly. But then I did not really try that much on it after I had it working good enough. I think it was something to do with some focusing, and I could have used the analog side and some DSP to clean it up, I'm sure, but then I would have probably spent a good six months on it.
The only problem is I wish I had bought several dozen of those little optical slot readers when I had the chance. Anybody seen any out there ( dirt cheap ones, I mean - you know those surplus ditties they sell for a buck )? I am looking for some that just have the raw serial bar-code sensor out because I feed it right into the AVR.
USB Keycards? (Score:3, Interesting)
Anyways I think that a standard USB "keycard" would be an awesome Linux project (sorry GNU/Linux) and I am totally suprised that I haven't seen one on SF. It makes me think I must be blind.