An optocoupler circuit includes first and second resistors, an optocoupler, a reference circuit, and a comparator. The optocoupler includes a light source and a phototransistor. The light source is connected to form a first voltage divider with the first resistor. The phototransistor is connected to form a second voltage divider with the second resistor. The optocoupler transitions an output of the second voltage divider between first and second levels. Magnitudes of the first and second levels are greater than zero. The reference circuit is configured to output a reference voltage. The comparator includes a first input and a second input. The first input receives an output of the first voltage divider. The second input receives the reference voltage. An output of the comparator transitions between a third level and a fourth level based on a comparison between the output of the first voltage divider and the reference voltage.

A thermostat for controlling an HVAC system in an enclosure may include a passive infrared sensor, an active infrared sensor, and an electronic display having a first mode and a second mode. The thermostat may also include one or more processors programmed to change a setpoint temperature of the thermostat to an energy-saving temperature upon detection of a non-occupancy condition for the enclosure. The processor(s) may detect the non-occupancy condition based at least in part on readings received from the passive infrared sensor. The processor(s) may also be programmed to change the electronic display from the first mode to the second mode upon detection of a person approaching the thermostat. The processor(s) may detect a person approaching the thermostat based at least in part on readings received from the active infrared sensor.

An optocoupler circuit includes first and second resistors, an optocoupler, a reference circuit, and a comparator. The optocoupler includes a light source and a phototransistor. The light source is connected to form a first voltage divider with the first resistor. The phototransistor is connected to form a second voltage divider with the second resistor. The optocoupler transitions an output of the second voltage divider between first and second levels. Magnitudes of the first and second levels are greater than zero. The reference circuit is configured to output a reference voltage. The comparator includes a first input and a second input. The first input receives an output of the first voltage divider. The second input receives the reference voltage. An output of the comparator transitions between a third level and a fourth level based on a comparison between the output of the first voltage divider and the reference voltage.

A smart-home device includes a user interface including an electronic display having a first display mode and a second display mode, the first display mode generally requiring more power than said second display mode. The device also includes a processing system in operative communication with one or more environmental sensors for determining at least one environmental condition. The device additionally includes at least one sensor configured to detect a physical closeness of a user to the at least one sensor. The processing system may be configured to cause the electronic display to be in the first display mode when a closeness threshold has been exceeded, where the processing system is further configured to automatically adjust the closeness threshold based at least in part on a historical plurality of physical closeness events as detected by the at least one sensor.

An occupancy sensing electronic thermostat is described that includes a thermostat body, an electronic display that is viewable by a user in front of the thermostat, a passive infrared sensor for measuring infrared energy and an infrared energy directing element formed integrally with a front surface of the thermostat body. The passive infrared sensor may be positioned behind the infrared energy directing element such that infrared energy is directed thereonto by the infrared energy directing element. The thermostat may also include a temperature sensor and a microprocessor programmed to detect occupancy based on measurements from the passive infrared sensor.

A wall-mountable programmable electronic thermostat for controlling an HVAC system is described. The thermostat includes a circular wall-mountable backplate with a central opening to allow for the passage of HVAC wires for electrical connection to the thermostat. The head unit body is also circular and is removeably mountable to the back plate. A plurality of wedge-shaped wiring terminals are mounted on the backplate for making a tool-free connection to HVAC wires. Each wiring terminal has button that a user can depress while a wire is inserted in a wire hole. The terminals are arranged along one or more circular arcs about the central opening of the backplate such that the wire holes face the central opening and the buttons are located close to the outer periphery of the backplate.

An occupancy sensing electronic thermostat is described that includes a thermostat body, an electronic display that is viewable by a user in front of the thermostat, a passive infrared sensor for measuring infrared energy and an infrared energy directing element formed integrally with a front surface of the thermostat body. The passive infrared sensor may be positioned behind the infrared energy directing element such that infrared energy is directed thereonto by the infrared energy directing element. The thermostat may also include a temperature sensor and a microprocessor programmed to detect occupancy based on measurements from the passive infrared sensor.

A thermostat may include a memory and a processing system. The processing system may operate by determining a set of wake-up conditions for the processor to enter into a second operating state from a first operating state, the set of wake-up conditions including at least one threshold value associated with at least one environmental and/or time-of-day condition; causing the set of wake-up conditions to be stored in a memory; operating in a first mode in which the processor is in the first operating state during a time interval subsequent to causing the set of wake-up conditions to be stored in the memory; determining, while the processor is in the first operating state, whether at least one of the set of wake-up conditions has been met; and then operating in a second mode in which the processor is in the second operating state.

An occupancy sensing electronic thermostat is described that includes a thermostat body, an electronic display that is viewable by a user in front of the thermostat, a passive infrared sensor for measuring infrared energy and an infrared energy directing element formed integrally with a front surface of the thermostat body. The passive infrared sensor may be positioned behind the infrared energy directing element such that infrared energy is directed thereonto by the infrared energy directing element. The thermostat may also include a temperature sensor and a microprocessor programmed to detect occupancy based on measurements from the passive infrared sensor.