Thermostat with self-configuring connections to facilitate do-it-yourself installation

A method for automating compatibility of a thermostat with HVAC systems that are either single-HVAC-transformer systems or dual-HVAC-transformer systems, the compatibility being automated in that a manual jumper installation is not required for adaptation to either single-HVAC-transformer systems or dual-HVAC-transformer systems, the thermostat including a plurality of HVAC wire connectors configured for receiving a corresponding plurality of HVAC control wires, wherein the HVAC wire connectors include a first call relay wire connector, a first power return wire connector, a second call relay wire connector, and a second power return wire connector, the method comprising:

• operatively connecting the first call relay wire connector to the first power return wire connector to actuate a first HVAC function;
• operatively connecting the second call relay wire connector to the second power return wire connector to actuate a second HVAC function;
• if first and second external wires have been inserted into the first and second power return wire connectors, respectively, then electrically isolating the first and second power return wire connectors by opening a pre-existing electrical connection between said first and second power return wire connectors;
• and
• otherwise, electrically shorting together the first and second power return wire connectors.

A thermostat configured for automated compatibility with HVAC systems that are either single-HVAC-transformer systems or dual-HVAC-transformer systems, the thermostat comprising:

• first and second power return wire connectors;
• an insertion sensing circuit coupled to said first and second power return wire connectors and configured such that:
• (i) if first and second external wires have been inserted into the first and second power return wire connectors, respectively, then the first and second power return wire connectors are electrically isolated from each other by opening a pre-existing electrical connection between said first and second power return wire connectors without requiring a manual jumper installation and without requiring a processing function from a digital processor;
• and
• (ii) otherwise, the first and second power return wire connectors are electrically shorted together.

A thermostat comprising:

• a first call relay wire connector;
• a second call relay wire connector;
• a common wire connector;
• power harvesting circuitry;
• an insertion sensing circuit, wherein:
• the insertion sensing circuit detects the presence of a common wire in the common wire connector and causes the power harvesting circuitry to harvest power from the common wire if the common wire is inserted into the common wire connector;
• the insertion sensing circuit further detects the presence of a first call relay wire in the first call relay connector and causes the power harvesting circuitry to harvest power from the first call relay wire if (a) the common wire is not inserted into the common wire connector, and (b) the first call relay wire in inserted into the first call relay connector;
• the insertion sensing circuitry further detects the presence of a second call relay wire in the second call relay wire connector and causes the power harvesting circuitry to harvest power from the second call relay wire if (a) the common wire is not inserted into the common wire connector, (b) the first call relay wire is not inserted into the first call relay wire connector, and (c) the second call relay wire is inserted into the second call relay connector.