Building sensor with self-configuring analog output circuit with fault detection

1. An environmental building sensor, the environmental building sensor comprising:

a sensing device configured to measure an environmental condition of a building;

an output connection between one or more circuits of the environmental building sensor and an external device, the output connection connected to an input impedance of the external device; and

the one or more circuits configured to:

detect a feedback voltage, the feedback voltage based on the input impedance;

determine, based on the feedback voltage, a type of analog input signal that the external device is configured to receive from the environmental building sensor, wherein the type of analog input signal is an analog current input or an analog voltage input; and

generate an analog input signal based on the determined type of analog input signal and the environmental condition measured by the sensing device and provide the analog input signal to the external device via the output connection.

2. The environmental building sensor of claim 1 , wherein the sensing device is configured to sense at least one of a temperature level of the building, a relative humidity (RH) level of the building, or a carbon dioxide (CO2) level of the building.

3. The environmental building sensor of claim 1 , wherein the one or more circuits are configured to:

detect a second feedback voltage; and

determine whether at least one of the environmental building sensor or the external device is experiencing a fault based on the second feedback voltage.

4. The environmental building sensor of claim 1 , wherein the one or more circuits are configured to:

generate the analog current input and provide the analog current input to the external device;

detect a second feedback voltage, wherein the second feedback voltage is a voltage across the input impedance; and

determine whether a fault exists in at least one of the environmental building sensor or the external device by comparing a voltage output generated by the one or more circuits to generate the analog current input to the second feedback voltage and determining that the voltage output is a maximum value.

5. The environmental building sensor of claim 4 , wherein the one or more circuits are configured to:

determine that the fault is an open circuit in response to a first determination that the second feedback voltage is equal to the voltage output and that the voltage output is the maximum value; and

determine that the fault is a lack of output headroom in response to a second determination that the second feedback voltage is less than the voltage output and that the voltage output is the maximum value.

6. The environmental building sensor of claim 1 , wherein the one or more circuits are configured to:

generate the analog voltage input and provide the analog voltage input to the external device;

detect a second feedback voltage; and

determine whether a fault exists in at least one of the environmental building sensor or the external device based on the second feedback voltage.

7. The environmental building sensor of claim 6 , wherein the fault is a short, wherein the one or more circuits are configured to determine whether the fault exists by determining whether the second feedback voltage is greater than or less than a predefined level.

8. The environmental building sensor of claim 6 , wherein the second feedback voltage is at least one of a third feedback voltage detected over a resistor of the one or more circuits in series with the input impedance of the external device or a fourth feedback voltage detected over the input impedance of the external device.

9. A building system of a building, the building system comprising:

a building controller comprising an input connection, wherein the input connection is associated with an input impedance, wherein the building controller is configured to receive an analog current input or an analog voltage input via the input connection and perform one or more control actions based on the analog current input or the analog voltage input; and

a building sensor comprising one or more circuits configured to:

detect a feedback voltage, the feedback voltage based on the input impedance;

determine, based on the feedback voltage, a type of analog input signal that the building controller is configured to receive from the building sensor, wherein the type of analog input signal is the analog current input or the analog voltage input; and

generate an analog input signal based on the determined type of analog input signal and a condition measured by a sensing device and provide the analog input signal to the building controller.

10. The building system of claim 9 , wherein the one or more circuits are configured to:

detect a second feedback voltage; and

determine whether at least one of the building sensor or the building controller is experiencing a fault based on the second feedback voltage.

11. The building system of claim 9 , wherein the one or more circuits are configured to:

generate the analog voltage input and provide the analog voltage input to the building controller;

detect a second feedback voltage; and

determine whether a fault exists in at least one of the building sensor or the building controller based on the second feedback voltage.

12. A self-configuring analog output circuit of a sensor, the self-configuring analog output circuit comprising one or more circuits configured to:

detect a feedback voltage, the feedback voltage based on an input impedance of an external device connected to the self-configuring analog output circuit;

determine, based on the feedback voltage, a type of analog input signal that the external device is configured to receive from the self-configuring analog output circuit, wherein the type of analog input signal is an analog current input or an analog voltage input; and

generate an analog input signal based on the determined type of analog input signal and a condition measured by a sensing device of the sensor and provide the analog input signal to the external device.

13. The circuit of claim 12 , wherein the one or more circuits are configured to:

detect a second feedback voltage; and

determine whether the circuit is experiencing a fault based on the second feedback voltage.