Method and apparatus for powering and signaling over a single wire pair

Abstract

A remote access granting system has a remote access requester that reads an identification code from a magnetic strip on a card and provides a sequence of request signals indicative of logical ones and zeros on separate conductors to a remote access interface. In response to the request signals, the remote access interface pulse modulates a DC voltage signal on a transmission line with a request pulse having a first pulsewidth indicative of a logical one or with a request pulse having a second pulsewidth indicative of a logical zero. A controller interface detects the pulse modulation on the DC voltage signal, demodulates the request pulses, and provides on separate conductors to a controller a first request pulse indicative of a logical one and a second request pulse indicative of a logical zero. The controller determines whether the sequence of request pulses matches a predetermined sequence. If there is a match, the controller provides a lamp enable signal indicative that access is being granted to the controller interface which in turn pulse modulates the DC voltage signal on the transmission line with an access granted signal having an amplitude less than the amplitude of the request pulses and having a frequency different than the frequency of the request pulses. The remote access interface demodulates the access granted signal and provides the lamp enable signal to the remote access requester to enable entry through a security door and to inform the user that such access has been granted.