Auxillary switch for multiplexed control and ground signal from a thermostat

摘要

An auxiliary switch is provided that allows a thermostat to use full wave rectification for power while still communicating control information to the auxiliary switch over a multiplexed ground-control line to control associated equipment.

主权项

1. An auxiliary switch for a thermostat employing full-wave rectification, the auxiliary switch comprising:
an alternating current (AC) power output terminal for coupling a full-wave AC signal to the thermostat; a ground-control output terminal for providing a thermostat ground reference to the thermostat over a common ground line; an adapter network connected between the ground-control output terminal and an auxiliary switch ground reference, the adapter network providing a maximum and minimum voltage drop between the auxiliary switch ground reference and the thermostat ground reference to provide a stable reference at an expected maximum current flow; and a controller for determining voltage differences in duration between a sensed voltage signal across the adapter network and an expected un-multiplexed voltage signal duration at periodic time intervals during positive voltage periods and negative voltage periods of the full-wave AC signal and for de-multiplexing control information bits multiplexed onto the common ground line by the thermostat based on the determined voltage differences in duration.