Re: [EE:] Ibutton Samples by "Robert B." .

The ibuttons aren't wireless (afaik), and don't do any sort of computations on their own. Really I think they're more like a 1-wire interface to a cheap durable and portable kbit of nonvolatile ram. The challenge/response scheme you outlined is clever, and I'll certainly remember it in the future. The issues you brought up about out-of-sync keys are also very valid. The lock portion of the circuit would have to save the key in non-volatile memory, and ensure that it is synced with the key after every unlock-event. In the event they do get out of sync, however, the lock would still open but give some indication of the out-of-sync status (most likely a flashing LED). Right now I'm leaning towards using the serial number as the unlock code, and the NVram number as an intrusion alert indicator which gives alert if the numbers are out of sync, then automatically resyncs. If the Ibutton could do its own processing then your challenge/response method would work very well, but as it is merely a static storage device I can't come up with a way to make it work. Other issues I've been thinking about are what to do if the power goes out? Eeek I'd hate to be locked out of my house in event of a power outage! I figured maybe add external power-up posts so at the very least it could be powered from outside by a battery to unlock the doors. There's always *two* big dogs... {Original Message removed}